[PATCH v4 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking

[PATCH v4 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking

[James Morse]

Hello!

Changes since v3 are to split the patches up at the end of the series a little
more, and to make resctrl_arch_rmid_read() re-entrant which is needed before a
nohz_full CPU can call it in process context, and then be IPI'd from another
CPU. Otherwise changes since v3 are noted in each patch.
~
This series does two things, it changes resctrl to call resctrl_arch_rmid_read()
in a way that works for MPAM, and it separates the locking so that the arch code
and filesystem code don't have to share a mutex. I tried to split this as two
series, but these touch similar call sites, so it would create more work.

(What's MPAM? See the cover letter of the first series. [1])

On x86 the RMID is an independent number. MPAMs equivalent is PMG, but this
isn't an independent number - it extends the PARTID (same as CLOSID) space
with bits that aren't used to select the configuration. The monitors can
then be told to match specific PMG values, allowing monitor-groups to be
created.

But, MPAM expects the monitors to always monitor by PARTID. The
Cache-storage-utilisation counters can only work this way.
(In the MPAM spec not setting the MATCH_PARTID bit is made CONSTRAINED
UNPREDICTABLE - which is Arm's term to mean portable software can't rely on
this)

It gets worse, as some SoCs may have very few PMG bits. I've seen the
datasheet for one that has a single bit of PMG space.

To be usable, MPAM's counters always need the PARTID and the PMG.
For resctrl, this means always making the CLOSID available when the RMID
is used.

To ensure RMID are always unique, this series combines the CLOSID and RMID
into an index, and manages RMID based on that. For x86, the index and RMID
would always be the same.


Currently the architecture specific code in the cpuhp callbacks takes the
rdtgroup_mutex. This means the filesystem code would have to export this
lock, resulting in an ill-defined interface between the two, and the possibility
of cross-architecture lock-ordering head aches.

The second part of this series adds a domain_list_lock to protect writes to the
domain list, and protects the domain list with RCU - or read_cpus_lock().

Use of RCU is to allow lockless readers of the domain list, today resctrl only has
one, rdt_bit_usage_show(). But to get MPAMs monitors working, its very likely
they'll need to be plumbed up to perf. The uncore PMU driver would be a second
lockless reader of the domain list.

This series is based on v6.4-rc1, and can be retrieved from:
https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/monitors_and_locking/v4

Bugs welcome,


Thanks,

James


[1] https://lore.kernel.org/lkml/20210728170637.25610-1-james.morse@arm.com/
[v1] https://lore.kernel.org/all/20221021131204.5581-1-james.morse@arm.com/
[v2] https://lore.kernel.org/lkml/20230113175459.14825-1-james.morse@arm.com/
[v3] https://lore.kernel.org/r/20230320172620.18254-1-james.morse@arm.com 

James Morse (24):
  x86/resctrl: Track the closid with the rmid
  x86/resctrl: Access per-rmid structures by index
  x86/resctrl: Create helper for RMID allocation and mondata dir
    creation
  x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare()
  x86/resctrl: Allow RMID allocation to be scoped by CLOSID
  x86/resctrl: Track the number of dirty RMID a CLOSID has
  x86/resctrl: Use set_bit()/clear_bit() instead of open coding
  x86/resctrl: Allocate the cleanest CLOSID by searching
    closid_num_dirty_rmid
  x86/resctrl: Move CLOSID/RMID matching and setting to use helpers
  tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef
  x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow
  x86/resctrl: Make resctrl_arch_rmid_read() retry when it is
    interrupted
  x86/resctrl: Queue mon_event_read() instead of sending an IPI
  x86/resctrl: Allow resctrl_arch_rmid_read() to sleep
  x86/resctrl: Allow arch to allocate memory needed in
    resctrl_arch_rmid_read()
  x86/resctrl: Make resctrl_mounted checks explicit
  x86/resctrl: Move alloc/mon static keys into helpers
  x86/resctrl: Make rdt_enable_key the arch's decision to switch
  x86/resctrl: Add helpers for system wide mon/alloc capable
  x86/resctrl: Add cpu online callback for resctrl work
  x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but
    cpu
  x86/resctrl: Add cpu offline callback for resctrl work
  x86/resctrl: Move domain helper migration into resctrl_offline_cpu()
  x86/resctrl: Separate arch and fs resctrl locks

 arch/x86/include/asm/resctrl.h            |  90 +++++
 arch/x86/kernel/cpu/resctrl/core.c        |  78 ++--
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  45 ++-
 arch/x86/kernel/cpu/resctrl/internal.h    |  81 ++++-
 arch/x86/kernel/cpu/resctrl/monitor.c     | 414 ++++++++++++++++------
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  15 +-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 335 ++++++++++++-----
 include/linux/resctrl.h                   |  42 ++-
 include/linux/tick.h                      |   9 +-
 9 files changed, 846 insertions(+), 263 deletions(-)

-- 
2.39.2

[PATCH v4 01/24] x86/resctrl: Track the closid with the rmid

[James Morse]

x86's RMID are independent of the CLOSID. An RMID can be allocated,
used and freed without considering the CLOSID.

MPAM's equivalent feature is PMG, which is not an independent number,
it extends the CLOSID/PARTID space. For MPAM, only PMG-bits worth of
'RMID' can be allocated for a single CLOSID.
i.e. if there is 1 bit of PMG space, then each CLOSID can have two
monitor groups.

To allow resctrl to disambiguate RMID values for different CLOSID,
everything in resctrl that keeps an RMID value needs to know the CLOSID
too. This will always be ignored on x86.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
Signed-off-by: James Morse <james.morse@arm.com>

---
Is there a better term for 'the unique identifier for a monitor group'.
Using RMID for that here may be confusing...

Changes since v1:
 * Added comment in struct rmid_entry

Changes since v2:
 * Moved X86_RESCTRL_BAD_CLOSID from a subsequent patch
---
 arch/x86/include/asm/resctrl.h            |  7 +++
 arch/x86/kernel/cpu/resctrl/internal.h    |  2 +-
 arch/x86/kernel/cpu/resctrl/monitor.c     | 65 ++++++++++++++---------
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  4 +-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 12 ++---
 include/linux/resctrl.h                   | 11 +++-
 6 files changed, 64 insertions(+), 37 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 255a78d9d906..e906070285fb 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -7,6 +7,13 @@
 #include <linux/sched.h>
 #include <linux/jump_label.h>
 
+/*
+ * This value can never be a valid CLOSID, and is used when mapping a
+ * (closid, rmid) pair to an index and back. On x86 only the RMID is
+ * needed.
+ */
+#define X86_RESCTRL_BAD_CLOSID         ((u32)~0)
+
 /**
  * struct resctrl_pqr_state - State cache for the PQR MSR
  * @cur_rmid:		The cached Resource Monitoring ID
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 85ceaf9a31ac..f2da908bb079 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -535,7 +535,7 @@ struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r);
 int closids_supported(void);
 void closid_free(int closid);
 int alloc_rmid(void);
-void free_rmid(u32 rmid);
+void free_rmid(u32 closid, u32 rmid);
 int rdt_get_mon_l3_config(struct rdt_resource *r);
 bool __init rdt_cpu_has(int flag);
 void mon_event_count(void *info);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ded1fc7cb7cb..86574adedd64 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -25,6 +25,12 @@
 #include "internal.h"
 
 struct rmid_entry {
+	/*
+	 * Some architectures's resctrl_arch_rmid_read() needs the CLOSID value
+	 * in order to access the correct monitor. This field provides the
+	 * value to list walkers like __check_limbo(). On x86 this is ignored.
+	 */
+	u32				closid;
 	u32				rmid;
 	int				busy;
 	struct list_head		list;
@@ -136,7 +142,7 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned long val)
 	return val;
 }
 
-static inline struct rmid_entry *__rmid_entry(u32 rmid)
+static inline struct rmid_entry *__rmid_entry(u32 closid, u32 rmid)
 {
 	struct rmid_entry *entry;
 
@@ -190,7 +196,8 @@ static struct arch_mbm_state *get_arch_mbm_state(struct rdt_hw_domain *hw_dom,
 }
 
 void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
-			     u32 rmid, enum resctrl_event_id eventid)
+			     u32 closid, u32 rmid,
+			     enum resctrl_event_id eventid)
 {
 	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
 	struct arch_mbm_state *am;
@@ -230,7 +237,8 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
 }
 
 int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
-			   u32 rmid, enum resctrl_event_id eventid, u64 *val)
+			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
+			   u64 *val)
 {
 	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
 	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
@@ -285,9 +293,9 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 		if (nrmid >= r->num_rmid)
 			break;
 
-		entry = __rmid_entry(nrmid);
+		entry = __rmid_entry(X86_RESCTRL_BAD_CLOSID, nrmid);// temporary
 
-		if (resctrl_arch_rmid_read(r, d, entry->rmid,
+		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
 					   QOS_L3_OCCUP_EVENT_ID, &val)) {
 			rmid_dirty = true;
 		} else {
@@ -342,7 +350,8 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 	cpu = get_cpu();
 	list_for_each_entry(d, &r->domains, list) {
 		if (cpumask_test_cpu(cpu, &d->cpu_mask)) {
-			err = resctrl_arch_rmid_read(r, d, entry->rmid,
+			err = resctrl_arch_rmid_read(r, d, entry->closid,
+						     entry->rmid,
 						     QOS_L3_OCCUP_EVENT_ID,
 						     &val);
 			if (err || val <= resctrl_rmid_realloc_threshold)
@@ -366,7 +375,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 		list_add_tail(&entry->list, &rmid_free_lru);
 }
 
-void free_rmid(u32 rmid)
+void free_rmid(u32 closid, u32 rmid)
 {
 	struct rmid_entry *entry;
 
@@ -375,7 +384,7 @@ void free_rmid(u32 rmid)
 
 	lockdep_assert_held(&rdtgroup_mutex);
 
-	entry = __rmid_entry(rmid);
+	entry = __rmid_entry(closid, rmid);
 
 	if (is_llc_occupancy_enabled())
 		add_rmid_to_limbo(entry);
@@ -383,8 +392,8 @@ void free_rmid(u32 rmid)
 		list_add_tail(&entry->list, &rmid_free_lru);
 }
 
-static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 rmid,
-				       enum resctrl_event_id evtid)
+static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 closid,
+				       u32 rmid, enum resctrl_event_id evtid)
 {
 	switch (evtid) {
 	case QOS_L3_MBM_TOTAL_EVENT_ID:
@@ -396,20 +405,21 @@ static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 rmid,
 	}
 }
 
-static int __mon_event_count(u32 rmid, struct rmid_read *rr)
+static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
 {
 	struct mbm_state *m;
 	u64 tval = 0;
 
 	if (rr->first) {
-		resctrl_arch_reset_rmid(rr->r, rr->d, rmid, rr->evtid);
-		m = get_mbm_state(rr->d, rmid, rr->evtid);
+		resctrl_arch_reset_rmid(rr->r, rr->d, closid, rmid, rr->evtid);
+		m = get_mbm_state(rr->d, closid, rmid, rr->evtid);
 		if (m)
 			memset(m, 0, sizeof(struct mbm_state));
 		return 0;
 	}
 
-	rr->err = resctrl_arch_rmid_read(rr->r, rr->d, rmid, rr->evtid, &tval);
+	rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid, rr->evtid,
+					 &tval);
 	if (rr->err)
 		return rr->err;
 
@@ -429,7 +439,7 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
  * __mon_event_count() is compared with the chunks value from the previous
  * invocation. This must be called once per second to maintain values in MBps.
  */
-static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
+static void mbm_bw_count(u32 closid, u32 rmid, struct rmid_read *rr)
 {
 	struct mbm_state *m = &rr->d->mbm_local[rmid];
 	u64 cur_bw, bytes, cur_bytes;
@@ -459,7 +469,7 @@ void mon_event_count(void *info)
 
 	rdtgrp = rr->rgrp;
 
-	ret = __mon_event_count(rdtgrp->mon.rmid, rr);
+	ret = __mon_event_count(rdtgrp->closid, rdtgrp->mon.rmid, rr);
 
 	/*
 	 * For Ctrl groups read data from child monitor groups and
@@ -470,7 +480,8 @@ void mon_event_count(void *info)
 
 	if (rdtgrp->type == RDTCTRL_GROUP) {
 		list_for_each_entry(entry, head, mon.crdtgrp_list) {
-			if (__mon_event_count(entry->mon.rmid, rr) == 0)
+			if (__mon_event_count(rdtgrp->closid, entry->mon.rmid,
+					      rr) == 0)
 				ret = 0;
 		}
 	}
@@ -600,7 +611,8 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 	}
 }
 
-static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
+static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
+		       u32 closid, u32 rmid)
 {
 	struct rmid_read rr;
 
@@ -615,12 +627,12 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
 	if (is_mbm_total_enabled()) {
 		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
 		rr.val = 0;
-		__mon_event_count(rmid, &rr);
+		__mon_event_count(closid, rmid, &rr);
 	}
 	if (is_mbm_local_enabled()) {
 		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
 		rr.val = 0;
-		__mon_event_count(rmid, &rr);
+		__mon_event_count(closid, rmid, &rr);
 
 		/*
 		 * Call the MBA software controller only for the
@@ -628,7 +640,7 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
 		 * the software controller explicitly.
 		 */
 		if (is_mba_sc(NULL))
-			mbm_bw_count(rmid, &rr);
+			mbm_bw_count(closid, rmid, &rr);
 	}
 }
 
@@ -685,11 +697,11 @@ void mbm_handle_overflow(struct work_struct *work)
 	d = container_of(work, struct rdt_domain, mbm_over.work);
 
 	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
-		mbm_update(r, d, prgrp->mon.rmid);
+		mbm_update(r, d, prgrp->closid, prgrp->mon.rmid);
 
 		head = &prgrp->mon.crdtgrp_list;
 		list_for_each_entry(crgrp, head, mon.crdtgrp_list)
-			mbm_update(r, d, crgrp->mon.rmid);
+			mbm_update(r, d, crgrp->closid, crgrp->mon.rmid);
 
 		if (is_mba_sc(NULL))
 			update_mba_bw(prgrp, d);
@@ -732,10 +744,11 @@ static int dom_data_init(struct rdt_resource *r)
 	}
 
 	/*
-	 * RMID 0 is special and is always allocated. It's used for all
-	 * tasks that are not monitored.
+	 * RMID 0 is special and is always allocated. It's used for the
+	 * default_rdtgroup control group, which will be setup later. See
+	 * rdtgroup_setup_root().
 	 */
-	entry = __rmid_entry(0);
+	entry = __rmid_entry(0, 0);
 	list_del(&entry->list);
 
 	return 0;
diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index 458cb7419502..aeadaeb5df9a 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -738,7 +738,7 @@ int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp)
 	 * anymore when this group would be used for pseudo-locking. This
 	 * is safe to call on platforms not capable of monitoring.
 	 */
-	free_rmid(rdtgrp->mon.rmid);
+	free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
 
 	ret = 0;
 	goto out;
@@ -773,7 +773,7 @@ int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp)
 
 	ret = rdtgroup_locksetup_user_restore(rdtgrp);
 	if (ret) {
-		free_rmid(rdtgrp->mon.rmid);
+		free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
 		return ret;
 	}
 
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 6ad33f355861..ff9ccfcd18bd 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2701,7 +2701,7 @@ static void free_all_child_rdtgrp(struct rdtgroup *rdtgrp)
 
 	head = &rdtgrp->mon.crdtgrp_list;
 	list_for_each_entry_safe(sentry, stmp, head, mon.crdtgrp_list) {
-		free_rmid(sentry->mon.rmid);
+		free_rmid(sentry->closid, sentry->mon.rmid);
 		list_del(&sentry->mon.crdtgrp_list);
 
 		if (atomic_read(&sentry->waitcount) != 0)
@@ -2741,7 +2741,7 @@ static void rmdir_all_sub(void)
 		cpumask_or(&rdtgroup_default.cpu_mask,
 			   &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);
 
-		free_rmid(rdtgrp->mon.rmid);
+		free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
 
 		kernfs_remove(rdtgrp->kn);
 		list_del(&rdtgrp->rdtgroup_list);
@@ -3239,7 +3239,7 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 	return 0;
 
 out_idfree:
-	free_rmid(rdtgrp->mon.rmid);
+	free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
 out_destroy:
 	kernfs_put(rdtgrp->kn);
 	kernfs_remove(rdtgrp->kn);
@@ -3253,7 +3253,7 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 static void mkdir_rdt_prepare_clean(struct rdtgroup *rgrp)
 {
 	kernfs_remove(rgrp->kn);
-	free_rmid(rgrp->mon.rmid);
+	free_rmid(rgrp->closid, rgrp->mon.rmid);
 	rdtgroup_remove(rgrp);
 }
 
@@ -3402,7 +3402,7 @@ static int rdtgroup_rmdir_mon(struct rdtgroup *rdtgrp, cpumask_var_t tmpmask)
 	update_closid_rmid(tmpmask, NULL);
 
 	rdtgrp->flags = RDT_DELETED;
-	free_rmid(rdtgrp->mon.rmid);
+	free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
 
 	/*
 	 * Remove the rdtgrp from the parent ctrl_mon group's list
@@ -3448,8 +3448,8 @@ static int rdtgroup_rmdir_ctrl(struct rdtgroup *rdtgrp, cpumask_var_t tmpmask)
 	cpumask_or(tmpmask, tmpmask, &rdtgrp->cpu_mask);
 	update_closid_rmid(tmpmask, NULL);
 
+	free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
 	closid_free(rdtgrp->closid);
-	free_rmid(rdtgrp->mon.rmid);
 
 	rdtgroup_ctrl_remove(rdtgrp);
 
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 8334eeacfec5..7d80bae05f59 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -225,6 +225,8 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
  *			      for this resource and domain.
  * @r:			resource that the counter should be read from.
  * @d:			domain that the counter should be read from.
+ * @closid:		closid that matches the rmid. The counter may
+ *			match traffic of both closid and rmid, or rmid only.
  * @rmid:		rmid of the counter to read.
  * @eventid:		eventid to read, e.g. L3 occupancy.
  * @val:		result of the counter read in bytes.
@@ -235,20 +237,25 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
  * 0 on success, or -EIO, -EINVAL etc on error.
  */
 int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
-			   u32 rmid, enum resctrl_event_id eventid, u64 *val);
+			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
+			   u64 *val);
+
 
 /**
  * resctrl_arch_reset_rmid() - Reset any private state associated with rmid
  *			       and eventid.
  * @r:		The domain's resource.
  * @d:		The rmid's domain.
+ * @closid:	The closid that matches the rmid. Counters may match both
+ *		closid and rmid, or rmid only.
  * @rmid:	The rmid whose counter values should be reset.
  * @eventid:	The eventid whose counter values should be reset.
  *
  * This can be called from any CPU.
  */
 void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
-			     u32 rmid, enum resctrl_event_id eventid);
+			     u32 closid, u32 rmid,
+			     enum resctrl_event_id eventid);
 
 /**
  * resctrl_arch_reset_rmid_all() - Reset all private state associated with
-- 
2.39.2

Re: [PATCH v4 01/24] x86/resctrl: Track the closid with the rmid

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:
> x86's RMID are independent of the CLOSID. An RMID can be allocated,
> used and freed without considering the CLOSID.
> 
> MPAM's equivalent feature is PMG, which is not an independent number,
> it extends the CLOSID/PARTID space. For MPAM, only PMG-bits worth of
> 'RMID' can be allocated for a single CLOSID.
> i.e. if there is 1 bit of PMG space, then each CLOSID can have two
> monitor groups.
> 
> To allow resctrl to disambiguate RMID values for different CLOSID,
> everything in resctrl that keeps an RMID value needs to know the CLOSID
> too. This will always be ignored on x86.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> 
> ---
> Is there a better term for 'the unique identifier for a monitor group'.
> Using RMID for that here may be confusing...
> 
> Changes since v1:
>  * Added comment in struct rmid_entry
> 
> Changes since v2:
>  * Moved X86_RESCTRL_BAD_CLOSID from a subsequent patch
> ---
>  arch/x86/include/asm/resctrl.h            |  7 +++
>  arch/x86/kernel/cpu/resctrl/internal.h    |  2 +-
>  arch/x86/kernel/cpu/resctrl/monitor.c     | 65 ++++++++++++++---------
>  arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  4 +-
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 12 ++---
>  include/linux/resctrl.h                   | 11 +++-
>  6 files changed, 64 insertions(+), 37 deletions(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index 255a78d9d906..e906070285fb 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -7,6 +7,13 @@
>  #include <linux/sched.h>
>  #include <linux/jump_label.h>
>  
> +/*
> + * This value can never be a valid CLOSID, and is used when mapping a
> + * (closid, rmid) pair to an index and back. On x86 only the RMID is
> + * needed.
> + */
> +#define X86_RESCTRL_BAD_CLOSID         ((u32)~0)
> +

I do not think this name is appropriate considering that it is later used
in x86 normal operation. I understand naming is complicated, could
something like X86_RESCTRL_EMPTY_CLOSID be appropriate?

>  /**
>   * struct resctrl_pqr_state - State cache for the PQR MSR
>   * @cur_rmid:		The cached Resource Monitoring ID

...

> @@ -628,7 +640,7 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
>  		 * the software controller explicitly.
>  		 */
>  		if (is_mba_sc(NULL))
> -			mbm_bw_count(rmid, &rr);
> +			mbm_bw_count(closid, rmid, &rr);
>  	}
>  }
>  
> @@ -685,11 +697,11 @@ void mbm_handle_overflow(struct work_struct *work)
>  	d = container_of(work, struct rdt_domain, mbm_over.work);
>  
>  	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
> -		mbm_update(r, d, prgrp->mon.rmid);
> +		mbm_update(r, d, prgrp->closid, prgrp->mon.rmid);
>  
>  		head = &prgrp->mon.crdtgrp_list;
>  		list_for_each_entry(crgrp, head, mon.crdtgrp_list)
> -			mbm_update(r, d, crgrp->mon.rmid);
> +			mbm_update(r, d, crgrp->closid, crgrp->mon.rmid);
>  
>  		if (is_mba_sc(NULL))
>  			update_mba_bw(prgrp, d);
> @@ -732,10 +744,11 @@ static int dom_data_init(struct rdt_resource *r)
>  	}
>  
>  	/*
> -	 * RMID 0 is special and is always allocated. It's used for all
> -	 * tasks that are not monitored.
> +	 * RMID 0 is special and is always allocated. It's used for the

Considering this change it may be more specific to now state that both
CLOSID 0 and RMID 0 are special.

> +	 * default_rdtgroup control group, which will be setup later. See

default_rdtgroup -> rdtgroup_default

> +	 * rdtgroup_setup_root().
>  	 */
> -	entry = __rmid_entry(0);
> +	entry = __rmid_entry(0, 0);
>  	list_del(&entry->list);
>  
>  	return 0;

...

  
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 8334eeacfec5..7d80bae05f59 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -225,6 +225,8 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
>   *			      for this resource and domain.
>   * @r:			resource that the counter should be read from.
>   * @d:			domain that the counter should be read from.
> + * @closid:		closid that matches the rmid. The counter may
> + *			match traffic of both closid and rmid, or rmid only.

It may be helpful to be specific in the references to parameters:
	closid that matches @rmid. The counter may
	match traffic of both @closid and @rmid, or @rmid only.

The "counter may match" text is not specific. Can detail be added
on what decides whether a counter matches both closid and rmid, or
rmid only?

>   * @rmid:		rmid of the counter to read.
>   * @eventid:		eventid to read, e.g. L3 occupancy.
>   * @val:		result of the counter read in bytes.
> @@ -235,20 +237,25 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
>   * 0 on success, or -EIO, -EINVAL etc on error.
>   */
>  int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
> -			   u32 rmid, enum resctrl_event_id eventid, u64 *val);
> +			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
> +			   u64 *val);
> +
>  
>  /**
>   * resctrl_arch_reset_rmid() - Reset any private state associated with rmid
>   *			       and eventid.
>   * @r:		The domain's resource.
>   * @d:		The rmid's domain.
> + * @closid:	The closid that matches the rmid. Counters may match both
> + *		closid and rmid, or rmid only.

Same here.

>   * @rmid:	The rmid whose counter values should be reset.
>   * @eventid:	The eventid whose counter values should be reset.
>   *
>   * This can be called from any CPU.
>   */
>  void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
> -			     u32 rmid, enum resctrl_event_id eventid);
> +			     u32 closid, u32 rmid,
> +			     enum resctrl_event_id eventid);
>  
>  /**
>   * resctrl_arch_reset_rmid_all() - Reset all private state associated with


Reinette

[PATCH v4 02/24] x86/resctrl: Access per-rmid structures by index

[James Morse]

Because of the differences between Intel RDT/AMD QoS and Arm's MPAM
monitors, RMID values on arm64 are not unique unless the CLOSID is
also included. Bitmaps like rmid_busy_llc need to be sized by the
number of unique entries for this resource.

Add helpers to encode/decode the CLOSID and RMID to an index. The
domain's rmid_busy_llc and rmid_ptrs[] are then sized by index,
as are the domain mbm_local and mbm_total arrays.
On x86, the index is always just the RMID, so all these structures
remain the same size.

The index gives resctrl a unique value it can use to store monitor
values, and allows MPAM to decode the CLOSID when reading the hardware
counters.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v1:
 * Added X86_BAD_CLOSID macro to make it clear what this value means
 * Added second WARN_ON() for closid checking, and made both _ONCE()

Changes since v2:
 * Added RESCTRL_RESERVED_CLOSID
 * Removed a newline
 * Repharsed some comments
 * Renamed a variable 'ignore'd
 * Moved X86_RESCTRL_BAD_CLOSID to a previous patch

Changes since v3:
 * Changed a variable name
 * Fixed various typos
---
 arch/x86/include/asm/resctrl.h         | 17 ++++++
 arch/x86/kernel/cpu/resctrl/core.c     |  2 +-
 arch/x86/kernel/cpu/resctrl/internal.h |  1 +
 arch/x86/kernel/cpu/resctrl/monitor.c  | 84 +++++++++++++++++---------
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  7 ++-
 include/linux/resctrl.h                |  3 +
 6 files changed, 83 insertions(+), 31 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index e906070285fb..dd9b638d43c8 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -101,6 +101,23 @@ static inline void resctrl_sched_in(struct task_struct *tsk)
 		__resctrl_sched_in(tsk);
 }
 
+static inline u32 resctrl_arch_system_num_rmid_idx(void)
+{
+	/* RMID are independent numbers for x86. num_rmid_idx == num_rmid */
+	return boot_cpu_data.x86_cache_max_rmid + 1;
+}
+
+static inline void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid)
+{
+	*rmid = idx;
+	*closid = X86_RESCTRL_BAD_CLOSID;
+}
+
+static inline u32 resctrl_arch_rmid_idx_encode(u32 ignored, u32 rmid)
+{
+	return rmid;
+}
+
 void resctrl_cpu_detect(struct cpuinfo_x86 *c);
 
 #else
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 030d3b409768..4bea032d072e 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -600,7 +600,7 @@ static void clear_closid_rmid(int cpu)
 	state->default_rmid = 0;
 	state->cur_closid = 0;
 	state->cur_rmid = 0;
-	wrmsr(MSR_IA32_PQR_ASSOC, 0, 0);
+	wrmsr(MSR_IA32_PQR_ASSOC, 0, RESCTRL_RESERVED_CLOSID);
 }
 
 static int resctrl_online_cpu(unsigned int cpu)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index f2da908bb079..d571da4848a4 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -7,6 +7,7 @@
 #include <linux/kernfs.h>
 #include <linux/fs_context.h>
 #include <linux/jump_label.h>
+#include <asm/resctrl.h>
 
 #define L3_QOS_CDP_ENABLE		0x01ULL
 
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 86574adedd64..bcc25f5339c0 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -142,12 +142,29 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned long val)
 	return val;
 }
 
-static inline struct rmid_entry *__rmid_entry(u32 closid, u32 rmid)
+/*
+ * x86 and arm64 differ in their handling of monitoring.
+ * x86's RMID are an independent number, there is only one source of traffic
+ * with an RMID value of '1'.
+ * arm64's PMG extend the PARTID/CLOSID space, there are multiple sources of
+ * traffic with a PMG value of '1', one for each CLOSID, meaning the RMID
+ * value is no longer unique.
+ * To account for this, resctrl uses an index. On x86 this is just the RMID,
+ * on arm64 it encodes the CLOSID and RMID. This gives a unique number.
+ *
+ * The domain's rmid_busy_llc and rmid_ptrs are sized by index. The arch code
+ * must accept an attempt to read every index.
+ */
+static inline struct rmid_entry *__rmid_entry(u32 idx)
 {
 	struct rmid_entry *entry;
+	u32 closid, rmid;
 
-	entry = &rmid_ptrs[rmid];
-	WARN_ON(entry->rmid != rmid);
+	entry = &rmid_ptrs[idx];
+	resctrl_arch_rmid_idx_decode(idx, &closid, &rmid);
+
+	WARN_ON_ONCE(entry->closid != closid);
+	WARN_ON_ONCE(entry->rmid != rmid);
 
 	return entry;
 }
@@ -277,8 +294,9 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 void __check_limbo(struct rdt_domain *d, bool force_free)
 {
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
 	struct rmid_entry *entry;
-	u32 crmid = 1, nrmid;
+	u32 idx, cur_idx = 1;
 	bool rmid_dirty;
 	u64 val = 0;
 
@@ -289,12 +307,11 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 	 * RMID and move it to the free list when the counter reaches 0.
 	 */
 	for (;;) {
-		nrmid = find_next_bit(d->rmid_busy_llc, r->num_rmid, crmid);
-		if (nrmid >= r->num_rmid)
+		idx = find_next_bit(d->rmid_busy_llc, idx_limit, cur_idx);
+		if (idx >= idx_limit)
 			break;
 
-		entry = __rmid_entry(X86_RESCTRL_BAD_CLOSID, nrmid);// temporary
-
+		entry = __rmid_entry(idx);
 		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
 					   QOS_L3_OCCUP_EVENT_ID, &val)) {
 			rmid_dirty = true;
@@ -303,19 +320,21 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 		}
 
 		if (force_free || !rmid_dirty) {
-			clear_bit(entry->rmid, d->rmid_busy_llc);
+			clear_bit(idx, d->rmid_busy_llc);
 			if (!--entry->busy) {
 				rmid_limbo_count--;
 				list_add_tail(&entry->list, &rmid_free_lru);
 			}
 		}
-		crmid = nrmid + 1;
+		cur_idx = idx + 1;
 	}
 }
 
 bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
 {
-	return find_first_bit(d->rmid_busy_llc, r->num_rmid) != r->num_rmid;
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
+
+	return find_first_bit(d->rmid_busy_llc, idx_limit) != idx_limit;
 }
 
 /*
@@ -345,6 +364,9 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 	struct rdt_domain *d;
 	int cpu, err;
 	u64 val = 0;
+	u32 idx;
+
+	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
 
 	entry->busy = 0;
 	cpu = get_cpu();
@@ -364,7 +386,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 		 */
 		if (!has_busy_rmid(r, d))
 			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL);
-		set_bit(entry->rmid, d->rmid_busy_llc);
+		set_bit(idx, d->rmid_busy_llc);
 		entry->busy++;
 	}
 	put_cpu();
@@ -377,14 +399,16 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 
 void free_rmid(u32 closid, u32 rmid)
 {
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
 	struct rmid_entry *entry;
 
-	if (!rmid)
-		return;
-
 	lockdep_assert_held(&rdtgroup_mutex);
 
-	entry = __rmid_entry(closid, rmid);
+	/* do not allow the default rmid to be free'd */
+	if (!idx)
+		return;
+
+	entry = __rmid_entry(idx);
 
 	if (is_llc_occupancy_enabled())
 		add_rmid_to_limbo(entry);
@@ -395,11 +419,13 @@ void free_rmid(u32 closid, u32 rmid)
 static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 closid,
 				       u32 rmid, enum resctrl_event_id evtid)
 {
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
+
 	switch (evtid) {
 	case QOS_L3_MBM_TOTAL_EVENT_ID:
-		return &d->mbm_total[rmid];
+		return &d->mbm_total[idx];
 	case QOS_L3_MBM_LOCAL_EVENT_ID:
-		return &d->mbm_local[rmid];
+		return &d->mbm_local[idx];
 	default:
 		return NULL;
 	}
@@ -441,7 +467,8 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
  */
 static void mbm_bw_count(u32 closid, u32 rmid, struct rmid_read *rr)
 {
-	struct mbm_state *m = &rr->d->mbm_local[rmid];
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
+	struct mbm_state *m = &rr->d->mbm_local[idx];
 	u64 cur_bw, bytes, cur_bytes;
 
 	cur_bytes = rr->val;
@@ -531,7 +558,7 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 {
 	u32 closid, rmid, cur_msr_val, new_msr_val;
 	struct mbm_state *pmbm_data, *cmbm_data;
-	u32 cur_bw, delta_bw, user_bw;
+	u32 cur_bw, delta_bw, user_bw, idx;
 	struct rdt_resource *r_mba;
 	struct rdt_domain *dom_mba;
 	struct list_head *head;
@@ -544,7 +571,8 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 
 	closid = rgrp->closid;
 	rmid = rgrp->mon.rmid;
-	pmbm_data = &dom_mbm->mbm_local[rmid];
+	idx = resctrl_arch_rmid_idx_encode(closid, rmid);
+	pmbm_data = &dom_mbm->mbm_local[idx];
 
 	dom_mba = get_domain_from_cpu(smp_processor_id(), r_mba);
 	if (!dom_mba) {
@@ -727,19 +755,20 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 
 static int dom_data_init(struct rdt_resource *r)
 {
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
 	struct rmid_entry *entry = NULL;
-	int i, nr_rmids;
+	u32 idx;
+	int i;
 
-	nr_rmids = r->num_rmid;
-	rmid_ptrs = kcalloc(nr_rmids, sizeof(struct rmid_entry), GFP_KERNEL);
+	rmid_ptrs = kcalloc(idx_limit, sizeof(struct rmid_entry), GFP_KERNEL);
 	if (!rmid_ptrs)
 		return -ENOMEM;
 
-	for (i = 0; i < nr_rmids; i++) {
+	for (i = 0; i < idx_limit; i++) {
 		entry = &rmid_ptrs[i];
 		INIT_LIST_HEAD(&entry->list);
 
-		entry->rmid = i;
+		resctrl_arch_rmid_idx_decode(i, &entry->closid, &entry->rmid);
 		list_add_tail(&entry->list, &rmid_free_lru);
 	}
 
@@ -748,7 +777,8 @@ static int dom_data_init(struct rdt_resource *r)
 	 * default_rdtgroup control group, which will be setup later. See
 	 * rdtgroup_setup_root().
 	 */
-	entry = __rmid_entry(0, 0);
+	idx = resctrl_arch_rmid_idx_encode(RESCTRL_RESERVED_CLOSID, 0);
+	entry = __rmid_entry(idx);
 	list_del(&entry->list);
 
 	return 0;
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index ff9ccfcd18bd..023eae69f29e 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3604,16 +3604,17 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
 
 static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 {
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
 	size_t tsize;
 
 	if (is_llc_occupancy_enabled()) {
-		d->rmid_busy_llc = bitmap_zalloc(r->num_rmid, GFP_KERNEL);
+		d->rmid_busy_llc = bitmap_zalloc(idx_limit, GFP_KERNEL);
 		if (!d->rmid_busy_llc)
 			return -ENOMEM;
 	}
 	if (is_mbm_total_enabled()) {
 		tsize = sizeof(*d->mbm_total);
-		d->mbm_total = kcalloc(r->num_rmid, tsize, GFP_KERNEL);
+		d->mbm_total = kcalloc(idx_limit, tsize, GFP_KERNEL);
 		if (!d->mbm_total) {
 			bitmap_free(d->rmid_busy_llc);
 			return -ENOMEM;
@@ -3621,7 +3622,7 @@ static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 	}
 	if (is_mbm_local_enabled()) {
 		tsize = sizeof(*d->mbm_local);
-		d->mbm_local = kcalloc(r->num_rmid, tsize, GFP_KERNEL);
+		d->mbm_local = kcalloc(idx_limit, tsize, GFP_KERNEL);
 		if (!d->mbm_local) {
 			bitmap_free(d->rmid_busy_llc);
 			kfree(d->mbm_total);
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 7d80bae05f59..ff7452f644e4 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -6,6 +6,9 @@
 #include <linux/list.h>
 #include <linux/pid.h>
 
+/* CLOSID value used by the default control group */
+#define RESCTRL_RESERVED_CLOSID		0
+
 #ifdef CONFIG_PROC_CPU_RESCTRL
 
 int proc_resctrl_show(struct seq_file *m,
-- 
2.39.2

RE: [PATCH v4 02/24] x86/resctrl: Access per-rmid structures by index

[Shaopeng Tan (Fujitsu)]

Hello James,

> Because of the differences between Intel RDT/AMD QoS and Arm's MPAM
> monitors, RMID values on arm64 are not unique unless the CLOSID is also
> included. Bitmaps like rmid_busy_llc need to be sized by the number of unique
> entries for this resource.
> 
> Add helpers to encode/decode the CLOSID and RMID to an index. The
> domain's rmid_busy_llc and rmid_ptrs[] are then sized by index, as are the
> domain mbm_local and mbm_total arrays.
> On x86, the index is always just the RMID, so all these structures remain the
> same size.
> 
> The index gives resctrl a unique value it can use to store monitor values, and
> allows MPAM to decode the CLOSID when reading the hardware counters.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
>  * Added X86_BAD_CLOSID macro to make it clear what this value means
>  * Added second WARN_ON() for closid checking, and made both _ONCE()
> 
> Changes since v2:
>  * Added RESCTRL_RESERVED_CLOSID
>  * Removed a newline
>  * Repharsed some comments
>  * Renamed a variable 'ignore'd
>  * Moved X86_RESCTRL_BAD_CLOSID to a previous patch
> 
> Changes since v3:
>  * Changed a variable name
>  * Fixed various typos
> ---
>  arch/x86/include/asm/resctrl.h         | 17 ++++++
>  arch/x86/kernel/cpu/resctrl/core.c     |  2 +-
>  arch/x86/kernel/cpu/resctrl/internal.h |  1 +
> arch/x86/kernel/cpu/resctrl/monitor.c  | 84
> +++++++++++++++++---------
> arch/x86/kernel/cpu/resctrl/rdtgroup.c |  7 ++-
>  include/linux/resctrl.h                |  3 +
>  6 files changed, 83 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index e906070285fb..dd9b638d43c8 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -101,6 +101,23 @@ static inline void resctrl_sched_in(struct task_struct
> *tsk)
>  		__resctrl_sched_in(tsk);
>  }
> 
> +static inline u32 resctrl_arch_system_num_rmid_idx(void)
> +{
> +	/* RMID are independent numbers for x86. num_rmid_idx ==
> num_rmid */
> +	return boot_cpu_data.x86_cache_max_rmid + 1; }
> +
> +static inline void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid,
> +u32 *rmid) {
> +	*rmid = idx;
> +	*closid = X86_RESCTRL_BAD_CLOSID;
> +}
> +
> +static inline u32 resctrl_arch_rmid_idx_encode(u32 ignored, u32 rmid) {
> +	return rmid;
> +}
> +
>  void resctrl_cpu_detect(struct cpuinfo_x86 *c);
> 
>  #else
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c
> b/arch/x86/kernel/cpu/resctrl/core.c
> index 030d3b409768..4bea032d072e 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -600,7 +600,7 @@ static void clear_closid_rmid(int cpu)
>  	state->default_rmid = 0;
>  	state->cur_closid = 0;
>  	state->cur_rmid = 0;
> -	wrmsr(MSR_IA32_PQR_ASSOC, 0, 0);
> +	wrmsr(MSR_IA32_PQR_ASSOC, 0, RESCTRL_RESERVED_CLOSID);
>  }
> 
>  static int resctrl_online_cpu(unsigned int cpu) diff --git
> a/arch/x86/kernel/cpu/resctrl/internal.h
> b/arch/x86/kernel/cpu/resctrl/internal.h
> index f2da908bb079..d571da4848a4 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -7,6 +7,7 @@
>  #include <linux/kernfs.h>
>  #include <linux/fs_context.h>
>  #include <linux/jump_label.h>
> +#include <asm/resctrl.h>
> 
>  #define L3_QOS_CDP_ENABLE		0x01ULL
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 86574adedd64..bcc25f5339c0 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -142,12 +142,29 @@ static inline u64 get_corrected_mbm_count(u32 rmid,
> unsigned long val)
>  	return val;
>  }
> 
> -static inline struct rmid_entry *__rmid_entry(u32 closid, u32 rmid)
> +/*
> + * x86 and arm64 differ in their handling of monitoring.
> + * x86's RMID are an independent number, there is only one source of
> +traffic
> + * with an RMID value of '1'.
> + * arm64's PMG extend the PARTID/CLOSID space, there are multiple
> +sources of
> + * traffic with a PMG value of '1', one for each CLOSID, meaning the
> +RMID
> + * value is no longer unique.
> + * To account for this, resctrl uses an index. On x86 this is just the
> +RMID,
> + * on arm64 it encodes the CLOSID and RMID. This gives a unique number.
> + *
> + * The domain's rmid_busy_llc and rmid_ptrs are sized by index. The
> +arch code
> + * must accept an attempt to read every index.
> + */
> +static inline struct rmid_entry *__rmid_entry(u32 idx)
>  {
>  	struct rmid_entry *entry;
> +	u32 closid, rmid;
> 
> -	entry = &rmid_ptrs[rmid];
> -	WARN_ON(entry->rmid != rmid);
> +	entry = &rmid_ptrs[idx];
> +	resctrl_arch_rmid_idx_decode(idx, &closid, &rmid);
> +
> +	WARN_ON_ONCE(entry->closid != closid);
> +	WARN_ON_ONCE(entry->rmid != rmid);
> 
>  	return entry;
>  }
> @@ -277,8 +294,9 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct
> rdt_domain *d,  void __check_limbo(struct rdt_domain *d, bool force_free)  {
>  	struct rdt_resource *r =
> &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> +	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>  	struct rmid_entry *entry;
> -	u32 crmid = 1, nrmid;
> +	u32 idx, cur_idx = 1;
>  	bool rmid_dirty;
>  	u64 val = 0;
> 
> @@ -289,12 +307,11 @@ void __check_limbo(struct rdt_domain *d, bool
> force_free)
>  	 * RMID and move it to the free list when the counter reaches 0.
>  	 */
>  	for (;;) {
> -		nrmid = find_next_bit(d->rmid_busy_llc, r->num_rmid,
> crmid);
> -		if (nrmid >= r->num_rmid)
> +		idx = find_next_bit(d->rmid_busy_llc, idx_limit, cur_idx);
> +		if (idx >= idx_limit)
>  			break;
> 
> -		entry = __rmid_entry(X86_RESCTRL_BAD_CLOSID, nrmid);//
> temporary
> -
> +		entry = __rmid_entry(idx);
>  		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
>  					   QOS_L3_OCCUP_EVENT_ID,
> &val)) {
>  			rmid_dirty = true;
> @@ -303,19 +320,21 @@ void __check_limbo(struct rdt_domain *d, bool
> force_free)
>  		}
> 
>  		if (force_free || !rmid_dirty) {
> -			clear_bit(entry->rmid, d->rmid_busy_llc);
> +			clear_bit(idx, d->rmid_busy_llc);
>  			if (!--entry->busy) {
>  				rmid_limbo_count--;
>  				list_add_tail(&entry->list, &rmid_free_lru);
>  			}
>  		}
> -		crmid = nrmid + 1;
> +		cur_idx = idx + 1;
>  	}
>  }
> 
>  bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)  {
> -	return find_first_bit(d->rmid_busy_llc, r->num_rmid) !=
> r->num_rmid;
> +	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
> +
> +	return find_first_bit(d->rmid_busy_llc, idx_limit) != idx_limit;
>  }

"struct rdt_resource *r" is not used in this function.


Best regards,
Shaopeng TAN

Re: [PATCH v4 02/24] x86/resctrl: Access per-rmid structures by index

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:
> Because of the differences between Intel RDT/AMD QoS and Arm's MPAM
> monitors, RMID values on arm64 are not unique unless the CLOSID is

I find the above a bit confusing ... the theme seems to be "RMID values
on arm64 are not unique because they are different from Intel".
Compare to: "One of the differences between Intel RDT/AMD QoS and
Arm's MPAM monitors is that RMID values on arm64 are not unique unless
the CLOSID is also included."

> also included. Bitmaps like rmid_busy_llc need to be sized by the
> number of unique entries for this resource.
> 
> Add helpers to encode/decode the CLOSID and RMID to an index. The
> domain's rmid_busy_llc and rmid_ptrs[] are then sized by index,
> as are the domain mbm_local and mbm_total arrays.

You can use "[]" to indicate an array.

> On x86, the index is always just the RMID, so all these structures
> remain the same size.

I do not consider this accurate considering that the previous
patch increased the size of each element to support this change.

> The index gives resctrl a unique value it can use to store monitor
> values, and allows MPAM to decode the CLOSID when reading the hardware
> counters.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
>  * Added X86_BAD_CLOSID macro to make it clear what this value means
>  * Added second WARN_ON() for closid checking, and made both _ONCE()
> 
> Changes since v2:
>  * Added RESCTRL_RESERVED_CLOSID
>  * Removed a newline
>  * Repharsed some comments
>  * Renamed a variable 'ignore'd
>  * Moved X86_RESCTRL_BAD_CLOSID to a previous patch
> 
> Changes since v3:
>  * Changed a variable name
>  * Fixed various typos
> ---
>  arch/x86/include/asm/resctrl.h         | 17 ++++++
>  arch/x86/kernel/cpu/resctrl/core.c     |  2 +-
>  arch/x86/kernel/cpu/resctrl/internal.h |  1 +
>  arch/x86/kernel/cpu/resctrl/monitor.c  | 84 +++++++++++++++++---------
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |  7 ++-
>  include/linux/resctrl.h                |  3 +
>  6 files changed, 83 insertions(+), 31 deletions(-)
> 

...

> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 86574adedd64..bcc25f5339c0 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -142,12 +142,29 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned long val)
>  	return val;
>  }
>  
> -static inline struct rmid_entry *__rmid_entry(u32 closid, u32 rmid)
> +/*
> + * x86 and arm64 differ in their handling of monitoring.
> + * x86's RMID are an independent number, there is only one source of traffic
> + * with an RMID value of '1'.
> + * arm64's PMG extend the PARTID/CLOSID space, there are multiple sources of
> + * traffic with a PMG value of '1', one for each CLOSID, meaning the RMID
> + * value is no longer unique.
> + * To account for this, resctrl uses an index. On x86 this is just the RMID,
> + * on arm64 it encodes the CLOSID and RMID. This gives a unique number.
> + *
> + * The domain's rmid_busy_llc and rmid_ptrs are sized by index. The arch code

rmid_ptrs[]

> + * must accept an attempt to read every index.
> + */
> +static inline struct rmid_entry *__rmid_entry(u32 idx)
>  {
>  	struct rmid_entry *entry;
> +	u32 closid, rmid;
>  
> -	entry = &rmid_ptrs[rmid];
> -	WARN_ON(entry->rmid != rmid);
> +	entry = &rmid_ptrs[idx];
> +	resctrl_arch_rmid_idx_decode(idx, &closid, &rmid);
> +
> +	WARN_ON_ONCE(entry->closid != closid);
> +	WARN_ON_ONCE(entry->rmid != rmid);
>  
>  	return entry;
>  }

...

> @@ -377,14 +399,16 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  
>  void free_rmid(u32 closid, u32 rmid)
>  {
> +	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
>  	struct rmid_entry *entry;
>  
> -	if (!rmid)
> -		return;
> -
>  	lockdep_assert_held(&rdtgroup_mutex);
>  
> -	entry = __rmid_entry(closid, rmid);
> +	/* do not allow the default rmid to be free'd */
> +	if (!idx)
> +		return;
> +

The interface seem to become blurry here. There are new
architecture specific encode/decode callbacks while at the same
time there are a few requirements:
- closid 0 and rmid 0 are reserved
- closid 0 and rmid 0 must map to index 0 (the architecture
callbacks thus do not have must freedom here ... they must
return index 0 for closid 0 and rmid 0, no?).

It does seem a bit strange that the one layer provides values (0,0)
to other layer while requiring a specific answer (0).

What if RESCTRL_RESERVED_RMID is also introduced and before encoding
the CLOSID and RMID the core first checks if it is a reserved entry
being freed and exit early if this is the case?


> +	entry = __rmid_entry(idx);
>  
>  	if (is_llc_occupancy_enabled())
>  		add_rmid_to_limbo(entry);

...

> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 7d80bae05f59..ff7452f644e4 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -6,6 +6,9 @@
>  #include <linux/list.h>
>  #include <linux/pid.h>
>  
> +/* CLOSID value used by the default control group */
> +#define RESCTRL_RESERVED_CLOSID		0
> +

#define RESCTRL_RESERVED_RMID		0 ?

>  #ifdef CONFIG_PROC_CPU_RESCTRL
>  
>  int proc_resctrl_show(struct seq_file *m,


Reinette

Re: [PATCH v4 02/24] x86/resctrl: Access per-rmid structures by index

[James Morse]

Hi Reinette,

On 15/06/2023 23:03, Reinette Chatre wrote:
> On 5/25/2023 11:01 AM, James Morse wrote:
>> Because of the differences between Intel RDT/AMD QoS and Arm's MPAM
>> monitors, RMID values on arm64 are not unique unless the CLOSID is
> 
> I find the above a bit confusing ... the theme seems to be "RMID values
> on arm64 are not unique because they are different from Intel".
> Compare to: "One of the differences between Intel RDT/AMD QoS and
> Arm's MPAM monitors is that RMID values on arm64 are not unique unless
> the CLOSID is also included."

I'm not too sure what is confusing. I'll pad it out with an example.
Is this clearer?:
--------------%<--------------
x86 systems identify traffic using the CLOSID and RMID. The CLOSID is
used to lookup the control policy, the RMID is used for monitoring. For
x86 these are independent numbers.
Arm's MPAM has equivalent features PARTID and PMG, where the PARTID is
used to lookup the control policy. The PMG in contrast is a small number
of bits that are used to subdivide PARTID when monitoring. The
cache-occupancy monitors require the PARTID to be specified when monitoring.

This means MPAM's PMG field is not unique. There are multiple PMG-0, one
per allocated CLOSID/PARTID. If PMG is treated as equivalent to RMID, it
cannot be allocated as an independent number. Bitmaps like rmid_busy_llc
need to be sized by the number of unique entries for this resource.

Treat the combined CLOSID and RMID as an index, and provide architecture
helpers to pack and unpack an index. This makes the MPAM values unique.
The domain's rmid_busy_llc and rmid_ptrs[] are then sized by index, as
are domain mbm_local[] and mbm_total[].

x86 can ignore the CLOSID field when packing and unpacking an index, and
report as many indexes as RMID.
--------------%<--------------

>> also included. Bitmaps like rmid_busy_llc need to be sized by the
>> number of unique entries for this resource.
>>
>> Add helpers to encode/decode the CLOSID and RMID to an index. The
>> domain's rmid_busy_llc and rmid_ptrs[] are then sized by index,
>> as are the domain mbm_local and mbm_total arrays.
> 
> You can use "[]" to indicate an array.

>> On x86, the index is always just the RMID, so all these structures
>> remain the same size.
> 
> I do not consider this accurate considering that the previous
> patch increased the size of each element to support this change.

That is a different patch... My point here is that x86's array sizes don't get multiplied
by num_closid, as only arm64 needs that.

I've brushed that wording under the carpet in the text above.


>> The index gives resctrl a unique value it can use to store monitor
>> values, and allows MPAM to decode the CLOSID when reading the hardware
>> counters.

>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 86574adedd64..bcc25f5339c0 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c

>> @@ -377,14 +399,16 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>>  
>>  void free_rmid(u32 closid, u32 rmid)
>>  {
>> +	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
>>  	struct rmid_entry *entry;
>>  
>> -	if (!rmid)
>> -		return;
>> -
>>  	lockdep_assert_held(&rdtgroup_mutex);
>>  
>> -	entry = __rmid_entry(closid, rmid);
>> +	/* do not allow the default rmid to be free'd */
>> +	if (!idx)
>> +		return;
>> +
> 
> The interface seem to become blurry here. There are new
> architecture specific encode/decode callbacks while at the same
> time there are a few requirements:
> - closid 0 and rmid 0 are reserved

> - closid 0 and rmid 0 must map to index 0 (the architecture
> callbacks thus do not have must freedom here ... they must
> return index 0 for closid 0 and rmid 0, no?).

It's not supposed to matter, but I agree this check in free_rmid() doesn't decode the
index to check.


> It does seem a bit strange that the one layer provides values (0,0)
> to other layer while requiring a specific answer (0).
> 
> What if RESCTRL_RESERVED_RMID is also introduced and before encoding
> the CLOSID and RMID the core first checks if it is a reserved entry
> being freed and exit early if this is the case?

Sure, that makes this cleaner.


Thanks,

James

[PATCH v4 03/24] x86/resctrl: Create helper for RMID allocation and mondata dir creation

[James Morse]

When monitorrring is support, each monitor and control group is allocated
an RMID. For control groups, rdtgroup_mkdir_ctrl_mon() later goes on to
allocate the CLOSID.

MPAM's equivalent of RMID are not an independent number, so can't be
allocated until the CLOSID is known. An RMID allocation for one CLOSID
may fail, whereas another may succeed depending on how many monitor
groups a control group has.

The RMID allocation needs to move to be after the CLOSID has been
allocated.

To make a subsequent change that does this easier to read, move the RMID
allocation and mondata dir creation to a helper.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 42 +++++++++++++++++---------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 023eae69f29e..05774b185eec 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3152,6 +3152,30 @@ static int rdtgroup_init_alloc(struct rdtgroup *rdtgrp)
 	return ret;
 }
 
+static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
+{
+	int ret;
+
+	if (!rdt_mon_capable)
+		return 0;
+
+	ret = alloc_rmid();
+	if (ret < 0) {
+		rdt_last_cmd_puts("Out of RMIDs\n");
+		return ret;
+	}
+	rdtgrp->mon.rmid = ret;
+
+	ret = mkdir_mondata_all(rdtgrp->kn, rdtgrp, &rdtgrp->mon.mon_data_kn);
+	if (ret) {
+		rdt_last_cmd_puts("kernfs subdir error\n");
+		free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
+		return ret;
+	}
+
+	return 0;
+}
+
 static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 			     const char *name, umode_t mode,
 			     enum rdt_group_type rtype, struct rdtgroup **r)
@@ -3217,20 +3241,10 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 		goto out_destroy;
 	}
 
-	if (rdt_mon_capable) {
-		ret = alloc_rmid();
-		if (ret < 0) {
-			rdt_last_cmd_puts("Out of RMIDs\n");
-			goto out_destroy;
-		}
-		rdtgrp->mon.rmid = ret;
+	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
+	if (ret)
+		goto out_destroy;
 
-		ret = mkdir_mondata_all(kn, rdtgrp, &rdtgrp->mon.mon_data_kn);
-		if (ret) {
-			rdt_last_cmd_puts("kernfs subdir error\n");
-			goto out_idfree;
-		}
-	}
 	kernfs_activate(kn);
 
 	/*
@@ -3238,8 +3252,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 	 */
 	return 0;
 
-out_idfree:
-	free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
 out_destroy:
 	kernfs_put(rdtgrp->kn);
 	kernfs_remove(rdtgrp->kn);
-- 
2.39.2

Re: [PATCH v4 03/24] x86/resctrl: Create helper for RMID allocation and mondata dir creation

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:
> When monitorrring is support, each monitor and control group is allocated

"When monitorrring is support" -> "When monitoring is supported"?

> an RMID. For control groups, rdtgroup_mkdir_ctrl_mon() later goes on to
> allocate the CLOSID.
> 
> MPAM's equivalent of RMID are not an independent number, so can't be
> allocated until the CLOSID is known. An RMID allocation for one CLOSID
> may fail, whereas another may succeed depending on how many monitor
> groups a control group has.
> 
> The RMID allocation needs to move to be after the CLOSID has been
> allocated.
> 
> To make a subsequent change that does this easier to read, move the RMID
> allocation and mondata dir creation to a helper.

(nitpick) Could you please swap the two parts of the sentence to make the
changelog easier to parse? "Move the RMID allocation and mondata dir
creation to a helper to make the subsequent change that does this
easier to read."

> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Signed-off-by: James Morse <james.morse@arm.com>

Reinette

[PATCH v4 04/24] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare()

[James Morse]

RMID are allocated for each monitor or control group directory, because
each of these needs its own RMID. For control groups,
rdtgroup_mkdir_ctrl_mon() later goes on to allocate the CLOSID.

MPAM's equivalent of RMID is not an independent number, so can't be
allocated until the CLOSID is known. An RMID allocation for one CLOSID
may fail, whereas another may succeed depending on how many monitor
groups a control group has.

The RMID allocation needs to move to be after the CLOSID has been
allocated.

Move the RMID allocation out of mkdir_rdt_prepare() to occur in its caller,
after the mkdir_rdt_prepare() call. This allows the RMID allocator to
know the CLOSID.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v2:
 * Moved kernfs_activate() later to preserve atomicity of files being visible
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 35 +++++++++++++++++++-------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 05774b185eec..8346a8f2ff9f 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3176,6 +3176,12 @@ static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
 	return 0;
 }
 
+static void mkdir_rdt_prepare_rmid_free(struct rdtgroup *rgrp)
+{
+	if (rdt_mon_capable)
+		free_rmid(rgrp->closid, rgrp->mon.rmid);
+}
+
 static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 			     const char *name, umode_t mode,
 			     enum rdt_group_type rtype, struct rdtgroup **r)
@@ -3241,12 +3247,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 		goto out_destroy;
 	}
 
-	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
-	if (ret)
-		goto out_destroy;
-
-	kernfs_activate(kn);
-
 	/*
 	 * The caller unlocks the parent_kn upon success.
 	 */
@@ -3265,7 +3265,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 static void mkdir_rdt_prepare_clean(struct rdtgroup *rgrp)
 {
 	kernfs_remove(rgrp->kn);
-	free_rmid(rgrp->closid, rgrp->mon.rmid);
 	rdtgroup_remove(rgrp);
 }
 
@@ -3287,12 +3286,21 @@ static int rdtgroup_mkdir_mon(struct kernfs_node *parent_kn,
 	prgrp = rdtgrp->mon.parent;
 	rdtgrp->closid = prgrp->closid;
 
+	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
+	if (ret) {
+		mkdir_rdt_prepare_clean(rdtgrp);
+		goto out_unlock;
+	}
+
+	kernfs_activate(rdtgrp->kn);
+
 	/*
 	 * Add the rdtgrp to the list of rdtgrps the parent
 	 * ctrl_mon group has to track.
 	 */
 	list_add_tail(&rdtgrp->mon.crdtgrp_list, &prgrp->mon.crdtgrp_list);
 
+out_unlock:
 	rdtgroup_kn_unlock(parent_kn);
 	return ret;
 }
@@ -3323,10 +3331,17 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
 	ret = 0;
 
 	rdtgrp->closid = closid;
-	ret = rdtgroup_init_alloc(rdtgrp);
-	if (ret < 0)
+
+	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
+	if (ret)
 		goto out_id_free;
 
+	kernfs_activate(rdtgrp->kn);
+
+	ret = rdtgroup_init_alloc(rdtgrp);
+	if (ret < 0)
+		goto out_rmid_free;
+
 	list_add(&rdtgrp->rdtgroup_list, &rdt_all_groups);
 
 	if (rdt_mon_capable) {
@@ -3345,6 +3360,8 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
 
 out_del_list:
 	list_del(&rdtgrp->rdtgroup_list);
+out_rmid_free:
+	mkdir_rdt_prepare_rmid_free(rdtgrp);
 out_id_free:
 	closid_free(closid);
 out_common_fail:
-- 
2.39.2

Re: [PATCH v4 04/24] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare()

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:
> RMID are allocated for each monitor or control group directory, because
> each of these needs its own RMID. For control groups,
> rdtgroup_mkdir_ctrl_mon() later goes on to allocate the CLOSID.
> 
> MPAM's equivalent of RMID is not an independent number, so can't be
> allocated until the CLOSID is known. An RMID allocation for one CLOSID
> may fail, whereas another may succeed depending on how many monitor
> groups a control group has.
> 
> The RMID allocation needs to move to be after the CLOSID has been
> allocated.

This third paragraph seems redundant.

> 
> Move the RMID allocation out of mkdir_rdt_prepare() to occur in its caller,
> after the mkdir_rdt_prepare() call. This allows the RMID allocator to
> know the CLOSID.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v2:
>  * Moved kernfs_activate() later to preserve atomicity of files being visible
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 35 +++++++++++++++++++-------
>  1 file changed, 26 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 05774b185eec..8346a8f2ff9f 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3176,6 +3176,12 @@ static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
>  	return 0;
>  }
>  
> +static void mkdir_rdt_prepare_rmid_free(struct rdtgroup *rgrp)
> +{
> +	if (rdt_mon_capable)
> +		free_rmid(rgrp->closid, rgrp->mon.rmid);
> +}
> +
>  static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
>  			     const char *name, umode_t mode,
>  			     enum rdt_group_type rtype, struct rdtgroup **r)
> @@ -3241,12 +3247,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
>  		goto out_destroy;
>  	}
>  
> -	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> -	if (ret)
> -		goto out_destroy;
> -
> -	kernfs_activate(kn);
> -
>  	/*
>  	 * The caller unlocks the parent_kn upon success.
>  	 */
> @@ -3265,7 +3265,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
>  static void mkdir_rdt_prepare_clean(struct rdtgroup *rgrp)
>  {
>  	kernfs_remove(rgrp->kn);
> -	free_rmid(rgrp->closid, rgrp->mon.rmid);
>  	rdtgroup_remove(rgrp);
>  }
>  
> @@ -3287,12 +3286,21 @@ static int rdtgroup_mkdir_mon(struct kernfs_node *parent_kn,
>  	prgrp = rdtgrp->mon.parent;
>  	rdtgrp->closid = prgrp->closid;
>  
> +	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> +	if (ret) {
> +		mkdir_rdt_prepare_clean(rdtgrp);
> +		goto out_unlock;
> +	}
> +
> +	kernfs_activate(rdtgrp->kn);
> +
>  	/*
>  	 * Add the rdtgrp to the list of rdtgrps the parent
>  	 * ctrl_mon group has to track.
>  	 */
>  	list_add_tail(&rdtgrp->mon.crdtgrp_list, &prgrp->mon.crdtgrp_list);
>  
> +out_unlock:
>  	rdtgroup_kn_unlock(parent_kn);
>  	return ret;
>  }
> @@ -3323,10 +3331,17 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
>  	ret = 0;
>  
>  	rdtgrp->closid = closid;
> -	ret = rdtgroup_init_alloc(rdtgrp);
> -	if (ret < 0)
> +
> +	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> +	if (ret)
>  		goto out_id_free;
>  
> +	kernfs_activate(rdtgrp->kn);
> +

I can see why you added this kernfs_activate() here and it certainly matches
the resctrl pattern of its use. It does seem as though resctrl often calls
kernfs_activate() as it adds files instead of a single call when all files
are ready. This is not an issue with this patch but I do think this is an
area that deserves a closer look before any more additions.

Reinette

[PATCH v4 05/24] x86/resctrl: Allow RMID allocation to be scoped by CLOSID

[James Morse]

MPAMs RMID values are not unique unless the CLOSID is considered as well.

alloc_rmid() expects the RMID to be an independent number.

Pass the CLOSID in to alloc_rmid(). Use this to compare indexes when
allocating. If the CLOSID is not relevant to the index, this ends up
comparing the free RMID with itself, and the first free entry will be
used. With MPAM the CLOSID is included in the index, so this becomes a
walk of the free RMID entries, until one that matches the supplied
CLOSID is found.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v2;
 * Rephrased comment in resctrl_find_free_rmid() to describe this in terms of
   list_entry_first()
 * Rephrased comment above alloc_rmid()

Changes since v3:
 * Flipped conditions in alloc_rmid()
---
 arch/x86/kernel/cpu/resctrl/internal.h    |  2 +-
 arch/x86/kernel/cpu/resctrl/monitor.c     | 51 +++++++++++++++++------
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  2 +-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    |  2 +-
 4 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index d571da4848a4..23e20f89d2b3 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -535,7 +535,7 @@ void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp);
 struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r);
 int closids_supported(void);
 void closid_free(int closid);
-int alloc_rmid(void);
+int alloc_rmid(u32 closid);
 void free_rmid(u32 closid, u32 rmid);
 int rdt_get_mon_l3_config(struct rdt_resource *r);
 bool __init rdt_cpu_has(int flag);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index bcc25f5339c0..27e731c7de72 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -337,24 +337,49 @@ bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
 	return find_first_bit(d->rmid_busy_llc, idx_limit) != idx_limit;
 }
 
-/*
- * As of now the RMIDs allocation is global.
- * However we keep track of which packages the RMIDs
- * are used to optimize the limbo list management.
- */
-int alloc_rmid(void)
+static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
 {
-	struct rmid_entry *entry;
-
-	lockdep_assert_held(&rdtgroup_mutex);
+	struct rmid_entry *itr;
+	u32 itr_idx, cmp_idx;
 
 	if (list_empty(&rmid_free_lru))
-		return rmid_limbo_count ? -EBUSY : -ENOSPC;
+		return rmid_limbo_count ? ERR_PTR(-EBUSY) : ERR_PTR(-ENOSPC);
+
+	list_for_each_entry(itr, &rmid_free_lru, list) {
+		/*
+		 * get the index of this free RMID, and the index it would need
+		 * to be if it were used with this CLOSID.
+		 * If the CLOSID is irrelevant on this architecture, these will
+		 * always be the same meaning the compiler can reduce this loop
+		 * to a single list_entry_first() call.
+		 */
+		itr_idx = resctrl_arch_rmid_idx_encode(itr->closid, itr->rmid);
+		cmp_idx = resctrl_arch_rmid_idx_encode(closid, itr->rmid);
+
+		if (itr_idx == cmp_idx)
+			return itr;
+	}
+
+	return ERR_PTR(-ENOSPC);
+}
+
+/*
+ * For MPAM the RMID value is not unique, and has to be considered with
+ * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
+ * allows all domains to be managed by a single limbo list.
+ * Each domain also has a rmid_busy_llc to reduce the work of the limbo handler.
+ */
+int alloc_rmid(u32 closid)
+{
+	struct rmid_entry *entry;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	entry = resctrl_find_free_rmid(closid);
+	if (IS_ERR(entry))
+		return PTR_ERR(entry);
 
-	entry = list_first_entry(&rmid_free_lru,
-				 struct rmid_entry, list);
 	list_del(&entry->list);
-
 	return entry->rmid;
 }
 
diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index aeadaeb5df9a..5ebd6e54c7f2 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -763,7 +763,7 @@ int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp)
 	int ret;
 
 	if (rdt_mon_capable) {
-		ret = alloc_rmid();
+		ret = alloc_rmid(rdtgrp->closid);
 		if (ret < 0) {
 			rdt_last_cmd_puts("Out of RMIDs\n");
 			return ret;
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 8346a8f2ff9f..ba0595508b2f 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3159,7 +3159,7 @@ static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
 	if (!rdt_mon_capable)
 		return 0;
 
-	ret = alloc_rmid();
+	ret = alloc_rmid(rdtgrp->closid);
 	if (ret < 0) {
 		rdt_last_cmd_puts("Out of RMIDs\n");
 		return ret;
-- 
2.39.2

Re: [PATCH v4 05/24] x86/resctrl: Allow RMID allocation to be scoped by CLOSID

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:

> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index bcc25f5339c0..27e731c7de72 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -337,24 +337,49 @@ bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
>  	return find_first_bit(d->rmid_busy_llc, idx_limit) != idx_limit;
>  }
>  
> -/*
> - * As of now the RMIDs allocation is global.
> - * However we keep track of which packages the RMIDs
> - * are used to optimize the limbo list management.
> - */
> -int alloc_rmid(void)
> +static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
>  {
> -	struct rmid_entry *entry;
> -
> -	lockdep_assert_held(&rdtgroup_mutex);
> +	struct rmid_entry *itr;
> +	u32 itr_idx, cmp_idx;
>  
>  	if (list_empty(&rmid_free_lru))
> -		return rmid_limbo_count ? -EBUSY : -ENOSPC;
> +		return rmid_limbo_count ? ERR_PTR(-EBUSY) : ERR_PTR(-ENOSPC);
> +
> +	list_for_each_entry(itr, &rmid_free_lru, list) {
> +		/*
> +		 * get the index of this free RMID, and the index it would need
> +		 * to be if it were used with this CLOSID.

Please start sentences with a capital letter.

> +		 * If the CLOSID is irrelevant on this architecture, these will
> +		 * always be the same meaning the compiler can reduce this loop
> +		 * to a single list_entry_first() call.
> +		 */
> +		itr_idx = resctrl_arch_rmid_idx_encode(itr->closid, itr->rmid);
> +		cmp_idx = resctrl_arch_rmid_idx_encode(closid, itr->rmid);
> +
> +		if (itr_idx == cmp_idx)
> +			return itr;
> +	}
> +
> +	return ERR_PTR(-ENOSPC);
> +}
> +

Reinette

[PATCH v4 06/24] x86/resctrl: Track the number of dirty RMID a CLOSID has

[James Morse]

MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be
used for different control groups.

This means once a CLOSID is allocated, all its monitoring ids may still be
dirty, and held in limbo.

Keep track of the number of RMID held in limbo each CLOSID has. This will
allow a future helper to find the 'cleanest' CLOSID when allocating.

The array is only needed when CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID is
defined. This will never be the case on x86.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/monitor.c | 43 +++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 27e731c7de72..1e7fa40ee471 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -43,6 +43,13 @@ struct rmid_entry {
  */
 static LIST_HEAD(rmid_free_lru);
 
+/**
+ * @closid_num_dirty_rmid    The number of dirty RMID each CLOSID has.
+ * Only allocated when CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID is defined.
+ * Indexed by CLOSID. Protected by rdtgroup_mutex.
+ */
+static int *closid_num_dirty_rmid;
+
 /**
  * @rmid_limbo_count     count of currently unused but (potentially)
  *     dirty RMIDs.
@@ -285,6 +292,17 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 	return 0;
 }
 
+static void limbo_release_entry(struct rmid_entry *entry)
+{
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	rmid_limbo_count--;
+	list_add_tail(&entry->list, &rmid_free_lru);
+
+	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
+		closid_num_dirty_rmid[entry->closid]--;
+}
+
 /*
  * Check the RMIDs that are marked as busy for this domain. If the
  * reported LLC occupancy is below the threshold clear the busy bit and
@@ -321,10 +339,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 
 		if (force_free || !rmid_dirty) {
 			clear_bit(idx, d->rmid_busy_llc);
-			if (!--entry->busy) {
-				rmid_limbo_count--;
-				list_add_tail(&entry->list, &rmid_free_lru);
-			}
+			if (!--entry->busy)
+				limbo_release_entry(entry);
 		}
 		cur_idx = idx + 1;
 	}
@@ -391,6 +407,8 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 	u64 val = 0;
 	u32 idx;
 
+	lockdep_assert_held(&rdtgroup_mutex);
+
 	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
 
 	entry->busy = 0;
@@ -420,6 +438,9 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 		rmid_limbo_count++;
 	else
 		list_add_tail(&entry->list, &rmid_free_lru);
+
+	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
+		closid_num_dirty_rmid[entry->closid]++;
 }
 
 void free_rmid(u32 closid, u32 rmid)
@@ -781,13 +802,25 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 static int dom_data_init(struct rdt_resource *r)
 {
 	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
+	u32 num_closid = resctrl_arch_get_num_closid(r);
 	struct rmid_entry *entry = NULL;
 	u32 idx;
 	int i;
 
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID)) {
+		closid_num_dirty_rmid = kcalloc(num_closid, sizeof(int),
+						GFP_KERNEL);
+		if (!closid_num_dirty_rmid)
+			return -ENOMEM;
+	}
+
 	rmid_ptrs = kcalloc(idx_limit, sizeof(struct rmid_entry), GFP_KERNEL);
-	if (!rmid_ptrs)
+	if (!rmid_ptrs) {
+		kfree(closid_num_dirty_rmid);
 		return -ENOMEM;
+	}
 
 	for (i = 0; i < idx_limit; i++) {
 		entry = &rmid_ptrs[i];
-- 
2.39.2

Re: [PATCH v4 06/24] x86/resctrl: Track the number of dirty RMID a CLOSID has

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:

...

> @@ -391,6 +407,8 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  	u64 val = 0;
>  	u32 idx;
>  
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
>  	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
>  
>  	entry->busy = 0;
> @@ -420,6 +438,9 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  		rmid_limbo_count++;
>  	else
>  		list_add_tail(&entry->list, &rmid_free_lru);
> +
> +	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
> +		closid_num_dirty_rmid[entry->closid]++;

Wouldn't this always increment the counter, whether the entry is
dirty or not? (Although ... the later change where entries are
always dirty may make this correct ... although I would still
expect the if statement that precedes it to change).

Reinette

Re: [PATCH v4 06/24] x86/resctrl: Track the number of dirty RMID a CLOSID has

[James Morse]

Hi Reinette,

On 6/15/23 23:08, Reinette Chatre wrote:
> On 5/25/2023 11:01 AM, James Morse wrote:
>> @@ -420,6 +438,9 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>>   		rmid_limbo_count++;
>>   	else
>>   		list_add_tail(&entry->list, &rmid_free_lru);
>> +
>> +	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
>> +		closid_num_dirty_rmid[entry->closid]++;
   
> Wouldn't this always increment the counter, whether the entry is
> dirty or not? (Although ... the later change where entries are
> always dirty may make this correct ... although I would still
> expect the if statement that precedes it to change).

True, I was expecting add_rmid_to_limbo() to always transiently add CLOSID to limbo,
hence this is unconditional, but you're right its optional - and this could cause everything
to pile up in the list when the limbo handler isn't running.
I'll add a check on entry->busy, and move this into the above if case.


Thanks,

James

[PATCH v4 07/24] x86/resctrl: Use set_bit()/clear_bit() instead of open coding

[James Morse]

The resctrl CLOSID allocator uses a single 32bit word to track which
CLOSID are free. The setting and clearing of bits is open coded.

A subsequent patch adds resctrl_closid_is_free(), which adds more open
coded bitmaps operations. These will eventually need changing to use
the bitops helpers so that a CLOSID bitmap of the correct size can be
allocated dynamically.

Convert the existing open coded bit manipulations of closid_free_map
to use set_bit() and friends.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index ba0595508b2f..6bf5623f82b4 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -106,7 +106,7 @@ void rdt_staged_configs_clear(void)
  * - Our choices on how to configure each resource become progressively more
  *   limited as the number of resources grows.
  */
-static int closid_free_map;
+static unsigned long closid_free_map;
 static int closid_free_map_len;
 
 int closids_supported(void)
@@ -126,7 +126,7 @@ static void closid_init(void)
 	closid_free_map = BIT_MASK(rdt_min_closid) - 1;
 
 	/* CLOSID 0 is always reserved for the default group */
-	closid_free_map &= ~1;
+	clear_bit(0, &closid_free_map);
 	closid_free_map_len = rdt_min_closid;
 }
 
@@ -137,14 +137,14 @@ static int closid_alloc(void)
 	if (closid == 0)
 		return -ENOSPC;
 	closid--;
-	closid_free_map &= ~(1 << closid);
+	clear_bit(closid, &closid_free_map);
 
 	return closid;
 }
 
 void closid_free(int closid)
 {
-	closid_free_map |= 1 << closid;
+	set_bit(closid, &closid_free_map);
 }
 
 /**
@@ -156,7 +156,7 @@ void closid_free(int closid)
  */
 static bool closid_allocated(unsigned int closid)
 {
-	return (closid_free_map & (1 << closid)) == 0;
+	return !test_bit(closid, &closid_free_map);
 }
 
 /**
-- 
2.39.2

[PATCH v4 08/24] x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid

[James Morse]

MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be
used for different control groups.

This means once a CLOSID is allocated, all its monitoring ids may still be
dirty, and held in limbo.

Instead of allocating the first free CLOSID, on architectures where
CONFIG_RESCTRL_RMID_DEPENDS_ON_COSID is enabled, search
closid_num_dirty_rmid[] to find the cleanest CLOSID.

The CLOSID found is returned to closid_alloc() for the free list
to be updated.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/internal.h |  2 ++
 arch/x86/kernel/cpu/resctrl/monitor.c  | 45 ++++++++++++++++++++++++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 ++++++++---
 3 files changed, 61 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 23e20f89d2b3..96fb7658ff74 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -557,5 +557,7 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
 void __init thread_throttle_mode_init(void);
 void __init mbm_config_rftype_init(const char *config);
 void rdt_staged_configs_clear(void);
+bool closid_allocated(unsigned int closid);
+int resctrl_find_cleanest_closid(void);
 
 #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 1e7fa40ee471..128d4c7206e4 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -379,6 +379,51 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
 	return ERR_PTR(-ENOSPC);
 }
 
+/**
+ * resctrl_find_cleanest_closid() - Find a CLOSID where all the associated
+ *                                  RMID are clean, or the CLOSID that has
+ *                                  the most clean RMID.
+ *
+ * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
+ * may not be able to allocate clean RMID. To avoid this the allocator will
+ * choose the CLOSID with the most clean RMID.
+ *
+ * When the CLOSID and RMID are independent numbers, the first free CLOSID will
+ * be returned.
+ *
+ * Call when CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID is defined. If not, call
+ * resctrl_closid_alloc_first_free() instead.
+ */
+int resctrl_find_cleanest_closid(void)
+{
+	u32 cleanest_closid = ~0, iter_num_dirty;
+	int i = 0;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
+		return -EIO;
+
+	for (i = 0; i < closids_supported(); i++) {
+		if (closid_allocated(i))
+			continue;
+
+		iter_num_dirty = closid_num_dirty_rmid[i];
+		if (iter_num_dirty == 0)
+			return i;
+
+		if (cleanest_closid == ~0)
+			cleanest_closid = i;
+
+		if (iter_num_dirty < closid_num_dirty_rmid[cleanest_closid])
+			cleanest_closid = i;
+	}
+
+	if (cleanest_closid == ~0)
+		return -ENOSPC;
+	return cleanest_closid;
+}
+
 /*
  * For MPAM the RMID value is not unique, and has to be considered with
  * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 6bf5623f82b4..1120c7700126 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -132,11 +132,20 @@ static void closid_init(void)
 
 static int closid_alloc(void)
 {
-	u32 closid = ffs(closid_free_map);
+	u32 closid;
+	int err;
 
-	if (closid == 0)
-		return -ENOSPC;
-	closid--;
+	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID)) {
+		err = resctrl_find_cleanest_closid();
+		if (err < 0)
+			return err;
+		closid = err;
+	} else {
+		closid = ffs(closid_free_map);
+		if (closid == 0)
+			return -ENOSPC;
+		closid--;
+	}
 	clear_bit(closid, &closid_free_map);
 
 	return closid;
@@ -154,7 +163,7 @@ void closid_free(int closid)
  * Return: true if @closid is currently associated with a resource group,
  * false if @closid is free
  */
-static bool closid_allocated(unsigned int closid)
+bool closid_allocated(unsigned int closid)
 {
 	return !test_bit(closid, &closid_free_map);
 }
-- 
2.39.2

Re: [PATCH v4 08/24] x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:

...

> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 1e7fa40ee471..128d4c7206e4 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -379,6 +379,51 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
>  	return ERR_PTR(-ENOSPC);
>  }
>  
> +/**
> + * resctrl_find_cleanest_closid() - Find a CLOSID where all the associated
> + *                                  RMID are clean, or the CLOSID that has
> + *                                  the most clean RMID.
> + *
> + * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
> + * may not be able to allocate clean RMID. To avoid this the allocator will
> + * choose the CLOSID with the most clean RMID.
> + *
> + * When the CLOSID and RMID are independent numbers, the first free CLOSID will
> + * be returned.
> + *
> + * Call when CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID is defined. If not, call
> + * resctrl_closid_alloc_first_free() instead.

I was not able to find where resctrl_closid_alloc_first_free() is introduced.

> + */
> +int resctrl_find_cleanest_closid(void)
> +{
> +	u32 cleanest_closid = ~0, iter_num_dirty;
> +	int i = 0;
> +
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
> +		return -EIO;
> +
> +	for (i = 0; i < closids_supported(); i++) {
> +		if (closid_allocated(i))
> +			continue;
> +
> +		iter_num_dirty = closid_num_dirty_rmid[i];
> +		if (iter_num_dirty == 0)
> +			return i;
> +
> +		if (cleanest_closid == ~0)
> +			cleanest_closid = i;
> +
> +		if (iter_num_dirty < closid_num_dirty_rmid[cleanest_closid])
> +			cleanest_closid = i;
> +	}
> +

Reinette

Re: [PATCH v4 08/24] x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid

[James Morse]

Hi Reinette,

On 6/15/23 23:09, Reinette Chatre wrote:
> On 5/25/2023 11:01 AM, James Morse wrote:
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 1e7fa40ee471..128d4c7206e4 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -379,6 +379,51 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
>>   	return ERR_PTR(-ENOSPC);
>>   }
>>   
>> +/**
>> + * resctrl_find_cleanest_closid() - Find a CLOSID where all the associated
>> + *                                  RMID are clean, or the CLOSID that has
>> + *                                  the most clean RMID.
>> + *
>> + * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
>> + * may not be able to allocate clean RMID. To avoid this the allocator will
>> + * choose the CLOSID with the most clean RMID.
>> + *
>> + * When the CLOSID and RMID are independent numbers, the first free CLOSID will
>> + * be returned.
>> + *
>> + * Call when CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID is defined. If not, call
>> + * resctrl_closid_alloc_first_free() instead.
> 
> I was not able to find where resctrl_closid_alloc_first_free() is introduced.

Oops, this was the name for the other half of closid_alloc() back when I thought it was more
readable to give it a name. The version posted leaves it alone to reduce the churn. I'll drop this paragraph.


Thanks,

James

[PATCH v4 09/24] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers

[James Morse]

When switching tasks, the CLOSID and RMID that the new task should
use are stored in struct task_struct. For x86 the CLOSID known by resctrl,
the value in task_struct, and the value written to the CPU register are
all the same thing.

MPAM's CPU interface has two different PARTID's one for data accesses
the other for instruction fetch. Storing resctrl's CLOSID value in
struct task_struct implies the arch code knows whether resctrl is using
CDP.

Move the matching and setting of the struct task_struct properties
to use helpers. This allows arm64 to store the hardware format of
the register, instead of having to convert it each time.

__rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn
values aren't seen as another CPU may schedule the task being moved
while the value is being changed. MPAM has an additional corner-case
here as the PMG bits extend the PARTID space. If the scheduler sees a
new-CLOSID but old-RMID, the task will dirty an RMID that the limbo code
is not watching causing an inaccurate count. x86's RMID are independent
values, so the limbo code will still be watching the old-RMID in this
circumstance.
To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together.
Both values must be provided together.

Because MPAM's RMID values are not unique, the CLOSID must be provided
when matching the RMID.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v2:
 * __rdtgroup_move_task() changed to set CLOSID from different CLOSID place
   depending on group type
---
 arch/x86/include/asm/resctrl.h         | 18 ++++++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 62 ++++++++++++++++----------
 2 files changed, 56 insertions(+), 24 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index dd9b638d43c8..78376c19ee6f 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -95,6 +95,24 @@ static inline unsigned int resctrl_arch_round_mon_val(unsigned int val)
 	return val * scale;
 }
 
+static inline void resctrl_arch_set_closid_rmid(struct task_struct *tsk,
+						u32 closid, u32 rmid)
+{
+	WRITE_ONCE(tsk->closid, closid);
+	WRITE_ONCE(tsk->rmid, rmid);
+}
+
+static inline bool resctrl_arch_match_closid(struct task_struct *tsk, u32 closid)
+{
+	return READ_ONCE(tsk->closid) == closid;
+}
+
+static inline bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 ignored,
+					   u32 rmid)
+{
+	return READ_ONCE(tsk->rmid) == rmid;
+}
+
 static inline void resctrl_sched_in(struct task_struct *tsk)
 {
 	if (static_branch_likely(&rdt_enable_key))
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 1120c7700126..f2bb3e09ed13 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -97,7 +97,7 @@ void rdt_staged_configs_clear(void)
  *
  * Using a global CLOSID across all resources has some advantages and
  * some drawbacks:
- * + We can simply set "current->closid" to assign a task to a resource
+ * + We can simply set current's closid to assign a task to a resource
  *   group.
  * + Context switch code can avoid extra memory references deciding which
  *   CLOSID to load into the PQR_ASSOC MSR
@@ -563,14 +563,26 @@ static void update_task_closid_rmid(struct task_struct *t)
 		_update_task_closid_rmid(t);
 }
 
+static bool task_in_rdtgroup(struct task_struct *tsk, struct rdtgroup *rdtgrp)
+{
+	u32 closid, rmid = rdtgrp->mon.rmid;
+
+	if (rdtgrp->type == RDTCTRL_GROUP)
+		closid = rdtgrp->closid;
+	else if (rdtgrp->type == RDTMON_GROUP)
+		closid = rdtgrp->mon.parent->closid;
+	else
+		return false;
+
+	return resctrl_arch_match_closid(tsk, closid) &&
+	       resctrl_arch_match_rmid(tsk, closid, rmid);
+}
+
 static int __rdtgroup_move_task(struct task_struct *tsk,
 				struct rdtgroup *rdtgrp)
 {
 	/* If the task is already in rdtgrp, no need to move the task. */
-	if ((rdtgrp->type == RDTCTRL_GROUP && tsk->closid == rdtgrp->closid &&
-	     tsk->rmid == rdtgrp->mon.rmid) ||
-	    (rdtgrp->type == RDTMON_GROUP && tsk->rmid == rdtgrp->mon.rmid &&
-	     tsk->closid == rdtgrp->mon.parent->closid))
+	if (task_in_rdtgroup(tsk, rdtgrp))
 		return 0;
 
 	/*
@@ -581,19 +593,19 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 	 * For monitor groups, can move the tasks only from
 	 * their parent CTRL group.
 	 */
-
-	if (rdtgrp->type == RDTCTRL_GROUP) {
-		WRITE_ONCE(tsk->closid, rdtgrp->closid);
-		WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
-	} else if (rdtgrp->type == RDTMON_GROUP) {
-		if (rdtgrp->mon.parent->closid == tsk->closid) {
-			WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
-		} else {
-			rdt_last_cmd_puts("Can't move task to different control group\n");
-			return -EINVAL;
-		}
+	if (rdtgrp->type == RDTMON_GROUP &&
+	    !resctrl_arch_match_closid(tsk, rdtgrp->mon.parent->closid)) {
+		rdt_last_cmd_puts("Can't move task to different control group\n");
+		return -EINVAL;
 	}
 
+	if (rdtgrp->type == RDTMON_GROUP)
+		resctrl_arch_set_closid_rmid(tsk, rdtgrp->mon.parent->closid,
+					     rdtgrp->mon.rmid);
+	else
+		resctrl_arch_set_closid_rmid(tsk, rdtgrp->closid,
+					     rdtgrp->mon.rmid);
+
 	/*
 	 * Ensure the task's closid and rmid are written before determining if
 	 * the task is current that will decide if it will be interrupted.
@@ -615,14 +627,15 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 
 static bool is_closid_match(struct task_struct *t, struct rdtgroup *r)
 {
-	return (rdt_alloc_capable &&
-	       (r->type == RDTCTRL_GROUP) && (t->closid == r->closid));
+	return (rdt_alloc_capable && (r->type == RDTCTRL_GROUP) &&
+		resctrl_arch_match_closid(t, r->closid));
 }
 
 static bool is_rmid_match(struct task_struct *t, struct rdtgroup *r)
 {
-	return (rdt_mon_capable &&
-	       (r->type == RDTMON_GROUP) && (t->rmid == r->mon.rmid));
+	return (rdt_mon_capable && (r->type == RDTMON_GROUP) &&
+		resctrl_arch_match_rmid(t, r->mon.parent->closid,
+					r->mon.rmid));
 }
 
 /**
@@ -818,7 +831,7 @@ int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
 		    rdtg->mode != RDT_MODE_EXCLUSIVE)
 			continue;
 
-		if (rdtg->closid != tsk->closid)
+		if (!resctrl_arch_match_closid(tsk, rdtg->closid))
 			continue;
 
 		seq_printf(s, "res:%s%s\n", (rdtg == &rdtgroup_default) ? "/" : "",
@@ -826,7 +839,8 @@ int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
 		seq_puts(s, "mon:");
 		list_for_each_entry(crg, &rdtg->mon.crdtgrp_list,
 				    mon.crdtgrp_list) {
-			if (tsk->rmid != crg->mon.rmid)
+			if (!resctrl_arch_match_rmid(tsk, crg->mon.parent->closid,
+						     crg->mon.rmid))
 				continue;
 			seq_printf(s, "%s", crg->kn->name);
 			break;
@@ -2678,8 +2692,8 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
 	for_each_process_thread(p, t) {
 		if (!from || is_closid_match(t, from) ||
 		    is_rmid_match(t, from)) {
-			WRITE_ONCE(t->closid, to->closid);
-			WRITE_ONCE(t->rmid, to->mon.rmid);
+			resctrl_arch_set_closid_rmid(t, to->closid,
+						     to->mon.rmid);
 
 			/*
 			 * Order the closid/rmid stores above before the loads
-- 
2.39.2

[PATCH v4 10/24] tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef

[James Morse]

tick_nohz_full_mask lists the CPUs that are nohz_full. This is only
needed when CONFIG_NO_HZ_FULL is defined. tick_nohz_full_cpu() allows
a specific CPU to be tested against the mask, and evaluates to false
when CONFIG_NO_HZ_FULL is not defined.

The resctrl code needs to pick a CPU to run some work on, a new helper
prefers housekeeping CPUs by examining the tick_nohz_full_mask. Hiding
the declaration behind #ifdef CONFIG_NO_HZ_FULL forces all the users to
be behind an ifdef too.

Move the tick_nohz_full_mask declaration, this lets callers drop the
ifdef, and guard access to tick_nohz_full_mask with IS_ENABLED() or
something like tick_nohz_full_cpu().

The definition does not need to be moved as any callers should be
removed at compile time unless CONFIG_NO_HZ_FULL is defined.

Signed-off-by: James Morse <james.morse@arm.com>
---
 include/linux/tick.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 9459fef5b857..65af90ca409a 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -174,9 +174,16 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
 static inline void tick_nohz_idle_stop_tick_protected(void) { }
 #endif /* !CONFIG_NO_HZ_COMMON */
 
+/*
+ * Mask of CPUs that are nohz_full.
+ *
+ * Users should be guarded by CONFIG_NO_HZ_FULL or a tick_nohz_full_cpu()
+ * check.
+ */
+extern cpumask_var_t tick_nohz_full_mask;
+
 #ifdef CONFIG_NO_HZ_FULL
 extern bool tick_nohz_full_running;
-extern cpumask_var_t tick_nohz_full_mask;
 
 static inline bool tick_nohz_full_enabled(void)
 {
-- 
2.39.2

[PATCH v4 11/24] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow

[James Morse]

The limbo and overflow code picks a CPU to use from the domain's list
of online CPUs. Work is then scheduled on these CPUs to maintain
the limbo list and any counters that may overflow.

cpumask_any() may pick a CPU that is marked nohz_full, which will
either penalise the work that CPU was dedicated to, or delay the
processing of limbo list or counters that may overflow. Perhaps
indefinitely. Delaying the overflow handling will skew the bandwidth
values calculated by mba_sc, which expects to be called once a second.

Add cpumask_any_housekeeping() as a replacement for cpumask_any()
that prefers housekeeping CPUs. This helper will still return
a nohz_full CPU if that is the only option. The CPU to use is
re-evaluated each time the limbo/overflow work runs. This ensures
the work will move off a nohz_full CPU once a housekeeping CPU is
available.

Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v3:
 * typos fixed
---
 arch/x86/kernel/cpu/resctrl/internal.h | 23 +++++++++++++++++++++++
 arch/x86/kernel/cpu/resctrl/monitor.c  | 17 ++++++++++++-----
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 96fb7658ff74..6f18cf26988c 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -7,6 +7,7 @@
 #include <linux/kernfs.h>
 #include <linux/fs_context.h>
 #include <linux/jump_label.h>
+#include <linux/tick.h>
 #include <asm/resctrl.h>
 
 #define L3_QOS_CDP_ENABLE		0x01ULL
@@ -55,6 +56,28 @@
 /* Max event bits supported */
 #define MAX_EVT_CONFIG_BITS		GENMASK(6, 0)
 
+/**
+ * cpumask_any_housekeeping() - Choose any CPU in @mask, preferring those that
+ *			        aren't marked nohz_full
+ * @mask:	The mask to pick a CPU from.
+ *
+ * Returns a CPU in @mask. If there are housekeeping CPUs that don't use
+ * nohz_full, these are preferred.
+ */
+static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
+{
+	int cpu, hk_cpu;
+
+	cpu = cpumask_any(mask);
+	if (tick_nohz_full_cpu(cpu)) {
+		hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
+		if (hk_cpu < nr_cpu_ids)
+			cpu = hk_cpu;
+	}
+
+	return cpu;
+}
+
 struct rdt_fs_context {
 	struct kernfs_fs_context	kfc;
 	bool				enable_cdpl2;
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 128d4c7206e4..e267869d60d5 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -770,9 +770,9 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
 void cqm_handle_limbo(struct work_struct *work)
 {
 	unsigned long delay = msecs_to_jiffies(CQM_LIMBOCHECK_INTERVAL);
-	int cpu = smp_processor_id();
 	struct rdt_resource *r;
 	struct rdt_domain *d;
+	int cpu;
 
 	mutex_lock(&rdtgroup_mutex);
 
@@ -781,8 +781,10 @@ void cqm_handle_limbo(struct work_struct *work)
 
 	__check_limbo(d, false);
 
-	if (has_busy_rmid(r, d))
+	if (has_busy_rmid(r, d)) {
+		cpu = cpumask_any_housekeeping(&d->cpu_mask);
 		schedule_delayed_work_on(cpu, &d->cqm_limbo, delay);
+	}
 
 	mutex_unlock(&rdtgroup_mutex);
 }
@@ -792,7 +794,7 @@ void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms)
 	unsigned long delay = msecs_to_jiffies(delay_ms);
 	int cpu;
 
-	cpu = cpumask_any(&dom->cpu_mask);
+	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
 	dom->cqm_work_cpu = cpu;
 
 	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
@@ -802,10 +804,10 @@ void mbm_handle_overflow(struct work_struct *work)
 {
 	unsigned long delay = msecs_to_jiffies(MBM_OVERFLOW_INTERVAL);
 	struct rdtgroup *prgrp, *crgrp;
-	int cpu = smp_processor_id();
 	struct list_head *head;
 	struct rdt_resource *r;
 	struct rdt_domain *d;
+	int cpu;
 
 	mutex_lock(&rdtgroup_mutex);
 
@@ -826,6 +828,11 @@ void mbm_handle_overflow(struct work_struct *work)
 			update_mba_bw(prgrp, d);
 	}
 
+	/*
+	 * Re-check for housekeeping CPUs. This allows the overflow handler to
+	 * move off a nohz_full CPU quickly.
+	 */
+	cpu = cpumask_any_housekeeping(&d->cpu_mask);
 	schedule_delayed_work_on(cpu, &d->mbm_over, delay);
 
 out_unlock:
@@ -839,7 +846,7 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 
 	if (!static_branch_likely(&rdt_mon_enable_key))
 		return;
-	cpu = cpumask_any(&dom->cpu_mask);
+	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
 	dom->mbm_work_cpu = cpu;
 	schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
 }
-- 
2.39.2

Re: [PATCH v4 11/24] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:

...

> @@ -55,6 +56,28 @@
>  /* Max event bits supported */
>  #define MAX_EVT_CONFIG_BITS		GENMASK(6, 0)
>  
> +/**
> + * cpumask_any_housekeeping() - Choose any CPU in @mask, preferring those that
> + *			        aren't marked nohz_full
> + * @mask:	The mask to pick a CPU from.
> + *
> + * Returns a CPU in @mask. If there are housekeeping CPUs that don't use
> + * nohz_full, these are preferred.
> + */
> +static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
> +{
> +	int cpu, hk_cpu;

Should both of these be unsigned int?

> +
> +	cpu = cpumask_any(mask);
> +	if (tick_nohz_full_cpu(cpu)) {
> +		hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
> +		if (hk_cpu < nr_cpu_ids)
> +			cpu = hk_cpu;
> +	}
> +
> +	return cpu;
> +}
> +
>  struct rdt_fs_context {
>  	struct kernfs_fs_context	kfc;
>  	bool				enable_cdpl2;
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 128d4c7206e4..e267869d60d5 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -770,9 +770,9 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
>  void cqm_handle_limbo(struct work_struct *work)
>  {
>  	unsigned long delay = msecs_to_jiffies(CQM_LIMBOCHECK_INTERVAL);
> -	int cpu = smp_processor_id();
>  	struct rdt_resource *r;
>  	struct rdt_domain *d;
> +	int cpu;
>  
>  	mutex_lock(&rdtgroup_mutex);
>  
> @@ -781,8 +781,10 @@ void cqm_handle_limbo(struct work_struct *work)
>  
>  	__check_limbo(d, false);
>  
> -	if (has_busy_rmid(r, d))
> +	if (has_busy_rmid(r, d)) {
> +		cpu = cpumask_any_housekeeping(&d->cpu_mask);
>  		schedule_delayed_work_on(cpu, &d->cqm_limbo, delay);

I expected cqm_work_cpu to also change when the worker moves to a different CPU.

> +	}
>  
>  	mutex_unlock(&rdtgroup_mutex);
>  }
> @@ -792,7 +794,7 @@ void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms)
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
>  
> -	cpu = cpumask_any(&dom->cpu_mask);
> +	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
>  	dom->cqm_work_cpu = cpu;
>  
>  	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> @@ -802,10 +804,10 @@ void mbm_handle_overflow(struct work_struct *work)
>  {
>  	unsigned long delay = msecs_to_jiffies(MBM_OVERFLOW_INTERVAL);
>  	struct rdtgroup *prgrp, *crgrp;
> -	int cpu = smp_processor_id();
>  	struct list_head *head;
>  	struct rdt_resource *r;
>  	struct rdt_domain *d;
> +	int cpu;
>  
>  	mutex_lock(&rdtgroup_mutex);
>  
> @@ -826,6 +828,11 @@ void mbm_handle_overflow(struct work_struct *work)
>  			update_mba_bw(prgrp, d);
>  	}
>  
> +	/*
> +	 * Re-check for housekeeping CPUs. This allows the overflow handler to
> +	 * move off a nohz_full CPU quickly.
> +	 */
> +	cpu = cpumask_any_housekeeping(&d->cpu_mask);
>  	schedule_delayed_work_on(cpu, &d->mbm_over, delay);

Here I expected mbm_work_cpu to change if the worker moves to a different CPU. 

>  
>  out_unlock:
> @@ -839,7 +846,7 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
>  
>  	if (!static_branch_likely(&rdt_mon_enable_key))
>  		return;
> -	cpu = cpumask_any(&dom->cpu_mask);
> +	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
>  	dom->mbm_work_cpu = cpu;
>  	schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
>  }

Reinette

[PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted

[James Morse]

resctrl_arch_rmid_read() could be called by resctrl in process context,
and then called by the PMU driver from irq context on the same CPU.
This could cause struct arch_mbm_state's prev_msr value to go backwards,
leading to the chunks value being incremented multiple times.

The struct arch_mbm_state holds both the previous msr value, and a count
of the number of chunks. These two fields need to be updated atomically.

Read the prev_msr before accessing the hardware, and cmpxchg() the value
back. If the value has changed, the whole thing is re-attempted.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/internal.h |  5 +++--
 arch/x86/kernel/cpu/resctrl/monitor.c  | 28 +++++++++++++++++++-------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 6f18cf26988c..7960366b9434 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -2,6 +2,7 @@
 #ifndef _ASM_X86_RESCTRL_INTERNAL_H
 #define _ASM_X86_RESCTRL_INTERNAL_H
 
+#include <linux/atomic.h>
 #include <linux/resctrl.h>
 #include <linux/sched.h>
 #include <linux/kernfs.h>
@@ -338,8 +339,8 @@ struct mbm_state {
  *		find this struct.
  */
 struct arch_mbm_state {
-	u64	chunks;
-	u64	prev_msr;
+	atomic64_t	chunks;
+	atomic64_t	prev_msr;
 };
 
 /**
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index e267869d60d5..1f470e55d555 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -225,13 +225,15 @@ void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
 {
 	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
 	struct arch_mbm_state *am;
+	u64 msr_val;
 
 	am = get_arch_mbm_state(hw_dom, rmid, eventid);
 	if (am) {
 		memset(am, 0, sizeof(*am));
 
 		/* Record any initial, non-zero count value. */
-		__rmid_read(rmid, eventid, &am->prev_msr);
+		__rmid_read(rmid, eventid, &msr_val);
+		atomic64_set(&am->prev_msr, msr_val);
 	}
 }
 
@@ -266,23 +268,35 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 {
 	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
 	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
+	u64 start_msr_val, old_msr_val, msr_val, chunks;
 	struct arch_mbm_state *am;
-	u64 msr_val, chunks;
-	int ret;
+	int ret = 0;
 
 	if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask))
 		return -EINVAL;
 
+interrupted:
+	am = get_arch_mbm_state(hw_dom, rmid, eventid);
+	if (am)
+		start_msr_val = atomic64_read(&am->prev_msr);
+
 	ret = __rmid_read(rmid, eventid, &msr_val);
 	if (ret)
 		return ret;
 
 	am = get_arch_mbm_state(hw_dom, rmid, eventid);
 	if (am) {
-		am->chunks += mbm_overflow_count(am->prev_msr, msr_val,
-						 hw_res->mbm_width);
-		chunks = get_corrected_mbm_count(rmid, am->chunks);
-		am->prev_msr = msr_val;
+		old_msr_val = atomic64_cmpxchg(&am->prev_msr, start_msr_val,
+					       msr_val);
+		if (old_msr_val != start_msr_val)
+			goto interrupted;
+
+		chunks = mbm_overflow_count(start_msr_val, msr_val,
+					    hw_res->mbm_width);
+		atomic64_add(chunks, &am->chunks);
+
+		chunks = get_corrected_mbm_count(rmid,
+						 atomic64_read(&am->chunks));
 	} else {
 		chunks = msr_val;
 	}
-- 
2.39.2

Re: [PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted

[Peter Newman]

Hi James,

On Thu, May 25, 2023 at 8:03 PM James Morse <james.morse@arm.com> wrote:
> +interrupted:
> +       am = get_arch_mbm_state(hw_dom, rmid, eventid);
> +       if (am)
> +               start_msr_val = atomic64_read(&am->prev_msr);
> +
>         ret = __rmid_read(rmid, eventid, &msr_val);
>         if (ret)
>                 return ret;
>
>         am = get_arch_mbm_state(hw_dom, rmid, eventid);
>         if (am) {
> -               am->chunks += mbm_overflow_count(am->prev_msr, msr_val,
> -                                                hw_res->mbm_width);
> -               chunks = get_corrected_mbm_count(rmid, am->chunks);
> -               am->prev_msr = msr_val;
> +               old_msr_val = atomic64_cmpxchg(&am->prev_msr, start_msr_val,
> +                                              msr_val);
> +               if (old_msr_val != start_msr_val)
> +                       goto interrupted;
> +
> +               chunks = mbm_overflow_count(start_msr_val, msr_val,
> +                                           hw_res->mbm_width);
> +               atomic64_add(chunks, &am->chunks);
> +
> +               chunks = get_corrected_mbm_count(rmid,
> +                                                atomic64_read(&am->chunks));
>         } else {
>                 chunks = msr_val;
>         }

It looks like if __rmid_read() is interrupted by an occupancy counter
read between writing QM_EVTSEL and reading QM_CTR, it will not perform
any update to am->prev_msr, and the interrupted read will return the
same counter value as in the interrupting read.

Maybe there's something you can create to check that's updated unconditionally?

-Peter

Re: [PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted

[James Morse]

Hi Peter,

On 06/06/2023 09:49, Peter Newman wrote:
> On Thu, May 25, 2023 at 8:03 PM James Morse <james.morse@arm.com> wrote:
>> +interrupted:
>> +       am = get_arch_mbm_state(hw_dom, rmid, eventid);
>> +       if (am)
>> +               start_msr_val = atomic64_read(&am->prev_msr);
>> +
>>         ret = __rmid_read(rmid, eventid, &msr_val);
>>         if (ret)
>>                 return ret;
>>
>>         am = get_arch_mbm_state(hw_dom, rmid, eventid);
>>         if (am) {
>> -               am->chunks += mbm_overflow_count(am->prev_msr, msr_val,
>> -                                                hw_res->mbm_width);
>> -               chunks = get_corrected_mbm_count(rmid, am->chunks);
>> -               am->prev_msr = msr_val;
>> +               old_msr_val = atomic64_cmpxchg(&am->prev_msr, start_msr_val,
>> +                                              msr_val);
>> +               if (old_msr_val != start_msr_val)
>> +                       goto interrupted;
>> +
>> +               chunks = mbm_overflow_count(start_msr_val, msr_val,
>> +                                           hw_res->mbm_width);
>> +               atomic64_add(chunks, &am->chunks);
>> +
>> +               chunks = get_corrected_mbm_count(rmid,
>> +                                                atomic64_read(&am->chunks));
>>         } else {
>>                 chunks = msr_val;
>>         }
> 
> It looks like if __rmid_read() is interrupted by an occupancy counter
> read between writing QM_EVTSEL and reading QM_CTR, it will not perform
> any update to am->prev_msr, and the interrupted read will return the
> same counter value as in the interrupting read.

Yup, that's a problem. I was only looking at the mbm state in memory, not the CPU register.
I think the fix is to read back QM_EVTSEL after reading QM_CTR. I'll do this in
__rmid_read() to avoid returning -EINTR. It creates two retry loops which is annoying, but
making the window larger means you're more likely to see false positives.

----------------------------%<----------------------------
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl
/monitor.c
index e24390d2e661..aeba035bb680 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -101,6 +101,7 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned
 long val)

 static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
 {
+       u32 _rmid, _eventid;
        u64 msr_val;

        /*
@@ -110,9 +111,15 @@ static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
         * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
         * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
         * are error bits.
+        * QM_EVTSEL is re-read to detect if this function was interrupted by
+        * another call, meaning the QM_CTR value may belong to a different
+        * event.
         */
-       wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
-       rdmsrl(MSR_IA32_QM_CTR, msr_val);
+       do {
+               wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
+               rdmsrl(MSR_IA32_QM_CTR, msr_val);
+               rdmsr(MSR_IA32_QM_EVTSEL, _eventid, _rmid);
+       } while (eventid != _eventid || rmid != _rmid);

        if (msr_val & RMID_VAL_ERROR)
                return -EIO;
----------------------------%<----------------------------


Thanks!

James

Re: [PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted

[Peter Newman]

Hi James,

On Tue, Jun 6, 2023 at 7:03 PM James Morse <james.morse@arm.com> wrote:
> On 06/06/2023 09:49, Peter Newman wrote:
> > It looks like if __rmid_read() is interrupted by an occupancy counter
> > read between writing QM_EVTSEL and reading QM_CTR, it will not perform
> > any update to am->prev_msr, and the interrupted read will return the
> > same counter value as in the interrupting read.
>
> Yup, that's a problem. I was only looking at the mbm state in memory, not the CPU register.
> I think the fix is to read back QM_EVTSEL after reading QM_CTR. I'll do this in
> __rmid_read() to avoid returning -EINTR. It creates two retry loops which is annoying, but
> making the window larger means you're more likely to see false positives.
>
> ----------------------------%<----------------------------
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl
> /monitor.c
> index e24390d2e661..aeba035bb680 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -101,6 +101,7 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned
>  long val)
>
>  static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
>  {
> +       u32 _rmid, _eventid;
>         u64 msr_val;
>
>         /*
> @@ -110,9 +111,15 @@ static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
>          * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
>          * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
>          * are error bits.
> +        * QM_EVTSEL is re-read to detect if this function was interrupted by
> +        * another call, meaning the QM_CTR value may belong to a different
> +        * event.
>          */
> -       wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
> -       rdmsrl(MSR_IA32_QM_CTR, msr_val);
> +       do {
> +               wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
> +               rdmsrl(MSR_IA32_QM_CTR, msr_val);
> +               rdmsr(MSR_IA32_QM_EVTSEL, _eventid, _rmid);
> +       } while (eventid != _eventid || rmid != _rmid);
>
>         if (msr_val & RMID_VAL_ERROR)
>                 return -EIO;

I happen to be tracking the cost of resctrl_arch_rmid_read() calls, so
I measured the impact of your fix on my AMD EPYC 7B12:

with both this and the soft RMID series[1] applied:

Base switch         7955     0.23%
Hard RMID Switch    8476     6.80%
Soft RMID Switch    10173   28.17%
CLOSID+Soft RMID    10740   35.32%

then adding EVTSEL read-back patch:

Base switch         7985
Hard RMID Switch    8540     6.96%
Soft RMID Switch    11015   37.95%
CLOSID+Soft RMID    11590   45.16%

The Soft RMID switches contain two __rmid_read() calls, so this
implies each QM_EVTSEL read-back is around 420 cycles on this AMD
implementation.

Even if you don't agree with my plan to add resctrl_arch_rmid_read()
calls to context switches, there should be cheaper ways to handle
this.

-Peter

[1] https://lore.kernel.org/lkml/20230421141723.2405942-4-peternewman@google.com/

Re: [PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted

[James Morse]

Hi Peter,

On 6/7/23 13:51, Peter Newman wrote:
> On Tue, Jun 6, 2023 at 7:03 PM James Morse <james.morse@arm.com> wrote:
>> On 06/06/2023 09:49, Peter Newman wrote:
>>> It looks like if __rmid_read() is interrupted by an occupancy counter
>>> read between writing QM_EVTSEL and reading QM_CTR, it will not perform
>>> any update to am->prev_msr, and the interrupted read will return the
>>> same counter value as in the interrupting read.
>>
>> Yup, that's a problem. I was only looking at the mbm state in memory, not the CPU register.
>> I think the fix is to read back QM_EVTSEL after reading QM_CTR. I'll do this in
>> __rmid_read() to avoid returning -EINTR. It creates two retry loops which is annoying, but
>> making the window larger means you're more likely to see false positives.
>>
>> ----------------------------%<----------------------------
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl
>> /monitor.c
>> index e24390d2e661..aeba035bb680 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -101,6 +101,7 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned
>>   long val)
>>
>>   static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
>>   {
>> +       u32 _rmid, _eventid;
>>          u64 msr_val;
>>
>>          /*
>> @@ -110,9 +111,15 @@ static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
>>           * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
>>           * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
>>           * are error bits.
>> +        * QM_EVTSEL is re-read to detect if this function was interrupted by
>> +        * another call, meaning the QM_CTR value may belong to a different
>> +        * event.
>>           */
>> -       wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
>> -       rdmsrl(MSR_IA32_QM_CTR, msr_val);
>> +       do {
>> +               wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
>> +               rdmsrl(MSR_IA32_QM_CTR, msr_val);
>> +               rdmsr(MSR_IA32_QM_EVTSEL, _eventid, _rmid);
>> +       } while (eventid != _eventid || rmid != _rmid);
>>
>>          if (msr_val & RMID_VAL_ERROR)
>>                  return -EIO;

> I happen to be tracking the cost of resctrl_arch_rmid_read() calls, so
> I measured the impact of your fix on my AMD EPYC 7B12:
> 
> with both this and the soft RMID series[1] applied:

> The Soft RMID switches contain two __rmid_read() calls, so this
> implies each QM_EVTSEL read-back is around 420 cycles on this AMD
> implementation.

Oooer. I assumed writes might have tedious side-effects but reads would cheap.
I suppose its because another CPU may have modified this value in the meantime.


> Even if you don't agree with my plan to add resctrl_arch_rmid_read()
> calls to context switches, there should be cheaper ways to handle
> this.

Yup, I've swapped this for a sequence counter[0], which should push that cost into the noise.
Anything left will be the cost of the atomics.


Thanks,

James

[0] barely tested:
------------------%<------------------
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 238831d53479..86d3a1b99be6 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -16,6 +16,7 @@
   */
  
  #include <linux/module.h>
+#include <linux/percpu.h>
  #include <linux/sizes.h>
  #include <linux/slab.h>
  
@@ -24,6 +25,9 @@
  
  #include "internal.h"
  
+/* Sequence number for writes to IA32 QM_EVTSEL */
+static DEFINE_PER_CPU(u64, qm_evtsel_seq);
+
  struct rmid_entry {
         /*
          * Some architectures's resctrl_arch_rmid_read() needs the CLOSID value
@@ -178,8 +182,7 @@ static inline struct rmid_entry *__rmid_entry(u32 idx)
  
  static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
  {
-       u32 _rmid, _eventid;
-       u64 msr_val;
+       u64 msr_val, seq;
  
         /*
          * As per the SDM, when IA32_QM_EVTSEL.EvtID (bits 7:0) is configured
@@ -188,15 +191,16 @@ static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
          * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
          * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
          * are error bits.
-        * QM_EVTSEL is re-read to detect if this function was interrupted by
-        * another call, meaning the QM_CTR value may belong to a different
-        * event.
+        * A per-cpu sequence counter is incremented each time QM_EVTSEL is
+        * written. This is used to detect if this function was interrupted by
+        * another call without re-reading the MSRs. Retry the MSR read when
+        * this happens as the QM_CTR value may belong to a different event.
          */
         do {
+               seq = this_cpu_inc_return(qm_evtsel_seq);
                 wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
                 rdmsrl(MSR_IA32_QM_CTR, msr_val);
-               rdmsr(MSR_IA32_QM_EVTSEL, _eventid, _rmid);
-       } while (eventid != _eventid || rmid != _rmid);
+       } while (seq != this_cpu_read(qm_evtsel_seq));
  
         if (msr_val & RMID_VAL_ERROR)
                 return -EIO;

------------------%<------------------

Re: [PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted

[Peter Newman]

Hi James,

On Thu, May 25, 2023 at 8:03 PM James Morse <james.morse@arm.com> wrote:
>
> resctrl_arch_rmid_read() could be called by resctrl in process context,
> and then called by the PMU driver from irq context on the same CPU.

Will there be x86 PMU changes to do this or is this only ARM? I just
want to make sure the x86 resctrl_arch_rmid_read() changes are
actually needed.

Thanks!
-Peter

Re: [PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted

[James Morse]

Hi Peter,

On 6/8/23 09:53, Peter Newman wrote:
> On Thu, May 25, 2023 at 8:03 PM James Morse <james.morse@arm.com> wrote:
>>
>> resctrl_arch_rmid_read() could be called by resctrl in process context,
>> and then called by the PMU driver from irq context on the same CPU.
> 
> Will there be x86 PMU changes to do this or is this only ARM? I just
> want to make sure the x86 resctrl_arch_rmid_read() changes are
> actually needed.

I plan to add that as an uncore 'resctrl_pmu' that works for all architectures by calling resctrl_arch_rmid_read(). Having that be specific to arm64 isn't helpful to user-space.
Perf is the natural home for these counters, and it will make it easier to add per-architecture
(or per-soc) counters, without having to teach resctrl about them.

This patch moved to be 'this' side of the 'move to /fs/resctrl' because this can happen
without the PMU changes. If a NOHZ_FULL CPU makes a syscall to read a counter, that happens
in process context, if a CPU in another domain wants to read the same counter, it has to send
an IPI which might target the same CPU.

(I've not investigated  whether this is an existing bug)


Thanks,

James

[PATCH v4 13/24] x86/resctrl: Queue mon_event_read() instead of sending an IPI

[James Morse]

Intel is blessed with an abundance of monitors, one per RMID, that can be
read from any CPU in the domain. MPAMs monitors reside in the MMIO MSC,
the number implemented is up to the manufacturer. This means when there are
fewer monitors than needed, they need to be allocated and freed.

MPAM's CSU monitors are used to back the 'llc_occupancy' monitor file. The
CSU counter is allowed to return 'not ready' for a small number of
micro-seconds after programming. To allow one CSU hardware monitor to be
used for multiple control or monitor groups, the CPU accessing the
monitor needs to be able to block when configuring and reading the
counter.

Worse, the domain may be broken up into slices, and the MMIO accesses
for each slice may need performing from different CPUs.

These two details mean MPAMs monitor code needs to be able to sleep, and
IPI another CPU in the domain to read from a resource that has been sliced.

mon_event_read() already invokes mon_event_count() via IPI, which means
this isn't possible. On systems using nohz-full, some CPUs need to be
interrupted to run kernel work as they otherwise stay in user-space
running realtime workloads. Interrupting these CPUs should be avoided,
and scheduling work on them may never complete.

Change mon_event_read() to pick a housekeeping CPU, (one that is not using
nohz_full) and schedule mon_event_count() and wait. If all the CPUs
in a domain are using nohz-full, then an IPI is used as the fallback.

This function is only used in response to a user-space filesystem request
(not the timing sensitive overflow code).

This allows MPAM to hide the slice behaviour from resctrl, and to keep
the monitor-allocation in monitor.c. When the IPI fallback is used on
machines where MPAM needs to make an access on multiple CPUs, the counter
read will always fail.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Peter Newman <peternewman@google.com>
Tested-by: Peter Newman <peternewman@google.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v2:
 * Use cpumask_any_housekeeping() and fallback to an IPI if needed.

Changes since v3:
 * Actually include the IPI fallback code.
---
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 28 +++++++++++++++++++++--
 arch/x86/kernel/cpu/resctrl/monitor.c     |  2 +-
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index b44c487727d4..6eeccad192ee 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -19,6 +19,7 @@
 #include <linux/kernfs.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
+#include <linux/tick.h>
 #include "internal.h"
 
 /*
@@ -520,12 +521,24 @@ int rdtgroup_schemata_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+static int smp_mon_event_count(void *arg)
+{
+	mon_event_count(arg);
+
+	return 0;
+}
+
 void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 		    struct rdt_domain *d, struct rdtgroup *rdtgrp,
 		    int evtid, int first)
 {
+	int cpu;
+
+	/* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */
+	lockdep_assert_held(&rdtgroup_mutex);
+
 	/*
-	 * setup the parameters to send to the IPI to read the data.
+	 * setup the parameters to pass to mon_event_count() to read the data.
 	 */
 	rr->rgrp = rdtgrp;
 	rr->evtid = evtid;
@@ -534,7 +547,18 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 	rr->val = 0;
 	rr->first = first;
 
-	smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);
+	cpu = cpumask_any_housekeeping(&d->cpu_mask);
+
+	/*
+	 * cpumask_any_housekeeping() prefers housekeeping CPUs, but
+	 * are all the CPUs nohz_full? If yes, pick a CPU to IPI.
+	 * MPAM's resctrl_arch_rmid_read() is unable to read the
+	 * counters on some platforms if its called in irq context.
+	 */
+	if (tick_nohz_full_cpu(cpu))
+		smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);
+	else
+		smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
 }
 
 int rdtgroup_mondata_show(struct seq_file *m, void *arg)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 1f470e55d555..6ba40495589a 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -589,7 +589,7 @@ static void mbm_bw_count(u32 closid, u32 rmid, struct rmid_read *rr)
 }
 
 /*
- * This is called via IPI to read the CQM/MBM counters
+ * This is scheduled by mon_event_read() to read the CQM/MBM counters
  * on a domain.
  */
 void mon_event_count(void *info)
-- 
2.39.2

Re: [PATCH v4 13/24] x86/resctrl: Queue mon_event_read() instead of sending an IPI

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:

...

> @@ -520,12 +521,24 @@ int rdtgroup_schemata_show(struct kernfs_open_file *of,
>  	return ret;
>  }
>  
> +static int smp_mon_event_count(void *arg)
> +{
> +	mon_event_count(arg);
> +
> +	return 0;
> +}
> +
>  void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  		    struct rdt_domain *d, struct rdtgroup *rdtgrp,
>  		    int evtid, int first)
>  {
> +	int cpu;
> +
> +	/* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
>  	/*
> -	 * setup the parameters to send to the IPI to read the data.
> +	 * setup the parameters to pass to mon_event_count() to read the data.
>  	 */

I understand that you are just copying existing comment but could you
please change it so that the sentence starts with a capital letter?

>  	rr->rgrp = rdtgrp;
>  	rr->evtid = evtid;
> @@ -534,7 +547,18 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  	rr->val = 0;
>  	rr->first = first;
>  
> -	smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);
> +	cpu = cpumask_any_housekeeping(&d->cpu_mask);
> +
> +	/*
> +	 * cpumask_any_housekeeping() prefers housekeeping CPUs, but
> +	 * are all the CPUs nohz_full? If yes, pick a CPU to IPI.
> +	 * MPAM's resctrl_arch_rmid_read() is unable to read the
> +	 * counters on some platforms if its called in irq context.
> +	 */
> +	if (tick_nohz_full_cpu(cpu))
> +		smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);
> +	else
> +		smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
>  }
>  

Reinette

[PATCH v4 14/24] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep

[James Morse]

MPAM's cache occupancy counters can take a little while to settle once
the monitor has been configured. The maximum settling time is described
to the driver via a firmware table. The value could be large enough
that it makes sense to sleep. To avoid exposing this to resctrl, it
should be hidden behind MPAM's resctrl_arch_rmid_read().

resctrl_arch_rmid_read() may be called via IPI meaning it is unable
to sleep. In this case resctrl_arch_rmid_read() should return an error
if it needs to sleep. This will only affect MPAM platforms where
the cache occupancy counter isn't available immediately, nohz_full is
in use, and there are there are no housekeeping CPUs in the necessary
domain.

There are three callers of resctrl_arch_rmid_read():
__mon_event_count() and __check_limbo() are both called from a
non-migrateable context. mon_event_read() invokes __mon_event_count()
using smp_call_on_cpu(), which adds work to the target CPUs workqueue.
rdtgroup_mutex() is held, meaning this cannot race with the resctrl
cpuhp callback. __check_limbo() is invoked via schedule_delayed_work_on()
also adds work to a per-cpu workqueue.

The remaining call is add_rmid_to_limbo() which is called in response
to a user-space syscall that frees an rmid. This opportunistically
reads the llc occupancy counter on the current domain to see if the
RMID is over the dirty threshold. This has to disable preemption to
avoid reading the wrong domain's value. Disabling pre-emption here
prevents resctrl_arch_rmid_read() from sleeping.

add_rmid_to_limbo() walks each domain, but only reads the counter
on one domain. If the system has more than one domain, the RMID will
always be added to the limbo list. If the RMIDs usage was not over the
threshold, it will be removed from the list when __check_limbo() runs.
Make this the default behaviour. Free RMIDs are always added to the
limbo list for each domain.

The user visible effect of this is that a clean RMID is not available
for re-allocation immediately after 'rmdir()' completes, this behaviour
was never portable as it never happened on a machine with multiple
domains.

Removing this path allows resctrl_arch_rmid_read() to sleep if its called
with interrupts unmasked. Document this is the expected behaviour, and
add a might_sleep() annotation to catch changes that won't work on arm64.

Signed-off-by: James Morse <james.morse@arm.com>
---
The previous version allowed resctrl_arch_rmid_read() to be called on the
wrong CPUs, but now that this needs to take nohz_full and housekeeping into
account, its too complex.

Changes since v3:
 * Removed error handling for smp_call_function_any(), this can't race
   with the cpuhp callbacks as both hold rdtgroup_mutex.
 * Switched to the alternative of removing the counter read, this simplifies
   things dramatically.
---
 arch/x86/kernel/cpu/resctrl/monitor.c | 15 ++-------------
 include/linux/resctrl.h               | 18 +++++++++++++++++-
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 6ba40495589a..fb33100e172b 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -272,6 +272,8 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 	struct arch_mbm_state *am;
 	int ret = 0;
 
+	resctrl_arch_rmid_read_context_check();
+
 	if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask))
 		return -EINVAL;
 
@@ -462,8 +464,6 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 {
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
 	struct rdt_domain *d;
-	int cpu, err;
-	u64 val = 0;
 	u32 idx;
 
 	lockdep_assert_held(&rdtgroup_mutex);
@@ -471,17 +471,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
 
 	entry->busy = 0;
-	cpu = get_cpu();
 	list_for_each_entry(d, &r->domains, list) {
-		if (cpumask_test_cpu(cpu, &d->cpu_mask)) {
-			err = resctrl_arch_rmid_read(r, d, entry->closid,
-						     entry->rmid,
-						     QOS_L3_OCCUP_EVENT_ID,
-						     &val);
-			if (err || val <= resctrl_rmid_realloc_threshold)
-				continue;
-		}
-
 		/*
 		 * For the first limbo RMID in the domain,
 		 * setup up the limbo worker.
@@ -491,7 +481,6 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 		set_bit(idx, d->rmid_busy_llc);
 		entry->busy++;
 	}
-	put_cpu();
 
 	if (entry->busy)
 		rmid_limbo_count++;
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index ff7452f644e4..b961936decfa 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -234,7 +234,12 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
  * @eventid:		eventid to read, e.g. L3 occupancy.
  * @val:		result of the counter read in bytes.
  *
- * Call from process context on a CPU that belongs to domain @d.
+ * Some architectures need to sleep when first programming some of the counters.
+ * (specifically: arm64's MPAM cache occupancy counters can return 'not ready'
+ *  for a short period of time). Call from a non-migrateable process context on
+ * a CPU that belongs to domain @d. e.g. use smp_call_on_cpu() or
+ * schedule_work_on(). This function can be called with interrupts masked,
+ * e.g. using smp_call_function_any(), but may concistently return an error.
  *
  * Return:
  * 0 on success, or -EIO, -EINVAL etc on error.
@@ -243,6 +248,17 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
 			   u64 *val);
 
+/**
+ * resctrl_arch_rmid_read_context_check()  - warn about invalid contexts
+ *
+ * When built with CONFIG_DEBUG_ATOMIC_SLEEP, this function will generate a
+ * warning when resctrl_arch_rmid_read() is called from an invalid context.
+ */
+static inline void resctrl_arch_rmid_read_context_check(void)
+{
+	if (!irqs_disabled())
+		might_sleep();
+}
 
 /**
  * resctrl_arch_reset_rmid() - Reset any private state associated with rmid
-- 
2.39.2

Re: [PATCH v4 14/24] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:
> MPAM's cache occupancy counters can take a little while to settle once
> the monitor has been configured. The maximum settling time is described
> to the driver via a firmware table. The value could be large enough
> that it makes sense to sleep. To avoid exposing this to resctrl, it
> should be hidden behind MPAM's resctrl_arch_rmid_read().
> 
> resctrl_arch_rmid_read() may be called via IPI meaning it is unable
> to sleep. In this case resctrl_arch_rmid_read() should return an error
> if it needs to sleep. This will only affect MPAM platforms where
> the cache occupancy counter isn't available immediately, nohz_full is
> in use, and there are there are no housekeeping CPUs in the necessary
> domain.
> 
> There are three callers of resctrl_arch_rmid_read():
> __mon_event_count() and __check_limbo() are both called from a
> non-migrateable context. mon_event_read() invokes __mon_event_count()
> using smp_call_on_cpu(), which adds work to the target CPUs workqueue.
> rdtgroup_mutex() is held, meaning this cannot race with the resctrl
> cpuhp callback. __check_limbo() is invoked via schedule_delayed_work_on()
> also adds work to a per-cpu workqueue.
> 
> The remaining call is add_rmid_to_limbo() which is called in response
> to a user-space syscall that frees an rmid. This opportunistically

rmid -> RMID

> reads the llc occupancy counter on the current domain to see if the

llc -> LLC

> RMID is over the dirty threshold. This has to disable preemption to
> avoid reading the wrong domain's value. Disabling pre-emption here
> prevents resctrl_arch_rmid_read() from sleeping.
> 
> add_rmid_to_limbo() walks each domain, but only reads the counter
> on one domain. If the system has more than one domain, the RMID will
> always be added to the limbo list. If the RMIDs usage was not over the
> threshold, it will be removed from the list when __check_limbo() runs.
> Make this the default behaviour. Free RMIDs are always added to the
> limbo list for each domain.
> 
> The user visible effect of this is that a clean RMID is not available
> for re-allocation immediately after 'rmdir()' completes, this behaviour
> was never portable as it never happened on a machine with multiple
> domains.
> 
> Removing this path allows resctrl_arch_rmid_read() to sleep if its called
> with interrupts unmasked. Document this is the expected behaviour, and
> add a might_sleep() annotation to catch changes that won't work on arm64.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> The previous version allowed resctrl_arch_rmid_read() to be called on the
> wrong CPUs, but now that this needs to take nohz_full and housekeeping into
> account, its too complex.
> 
> Changes since v3:
>  * Removed error handling for smp_call_function_any(), this can't race
>    with the cpuhp callbacks as both hold rdtgroup_mutex.
>  * Switched to the alternative of removing the counter read, this simplifies
>    things dramatically.
> ---
>  arch/x86/kernel/cpu/resctrl/monitor.c | 15 ++-------------
>  include/linux/resctrl.h               | 18 +++++++++++++++++-
>  2 files changed, 19 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 6ba40495589a..fb33100e172b 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -272,6 +272,8 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>  	struct arch_mbm_state *am;
>  	int ret = 0;
>  
> +	resctrl_arch_rmid_read_context_check();
> +
>  	if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask))
>  		return -EINVAL;
>  
> @@ -462,8 +464,6 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  {
>  	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>  	struct rdt_domain *d;
> -	int cpu, err;
> -	u64 val = 0;
>  	u32 idx;
>  
>  	lockdep_assert_held(&rdtgroup_mutex);
> @@ -471,17 +471,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
>  
>  	entry->busy = 0;
> -	cpu = get_cpu();
>  	list_for_each_entry(d, &r->domains, list) {
> -		if (cpumask_test_cpu(cpu, &d->cpu_mask)) {
> -			err = resctrl_arch_rmid_read(r, d, entry->closid,
> -						     entry->rmid,
> -						     QOS_L3_OCCUP_EVENT_ID,
> -						     &val);
> -			if (err || val <= resctrl_rmid_realloc_threshold)
> -				continue;
> -		}
> -
>  		/*
>  		 * For the first limbo RMID in the domain,
>  		 * setup up the limbo worker.
> @@ -491,7 +481,6 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  		set_bit(idx, d->rmid_busy_llc);
>  		entry->busy++;
>  	}
> -	put_cpu();
>  
>  	if (entry->busy)
>  		rmid_limbo_count++;

Would entry->busy ever be 0 after this change?

> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index ff7452f644e4..b961936decfa 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -234,7 +234,12 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
>   * @eventid:		eventid to read, e.g. L3 occupancy.
>   * @val:		result of the counter read in bytes.
>   *
> - * Call from process context on a CPU that belongs to domain @d.
> + * Some architectures need to sleep when first programming some of the counters.
> + * (specifically: arm64's MPAM cache occupancy counters can return 'not ready'
> + *  for a short period of time). Call from a non-migrateable process context on
> + * a CPU that belongs to domain @d. e.g. use smp_call_on_cpu() or
> + * schedule_work_on(). This function can be called with interrupts masked,
> + * e.g. using smp_call_function_any(), but may concistently return an error.
>   *

concistently -> consistently?

>   * Return:
>   * 0 on success, or -EIO, -EINVAL etc on error.
> @@ -243,6 +248,17 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>  			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
>  			   u64 *val);
>  
> +/**
> + * resctrl_arch_rmid_read_context_check()  - warn about invalid contexts
> + *
> + * When built with CONFIG_DEBUG_ATOMIC_SLEEP, this function will generate a
> + * warning when resctrl_arch_rmid_read() is called from an invalid context.

No need to say "this function" 
Could this comment be more specific about which contexts are invalid instead of
just referring to it as "invalid context". This seems to expect the reader to
already know what an invalid context would be. 

> + */
> +static inline void resctrl_arch_rmid_read_context_check(void)
> +{
> +	if (!irqs_disabled())
> +		might_sleep();
> +}

Could you please elaborate why the "!irqs_disabled()" is needed?

>  
>  /**
>   * resctrl_arch_reset_rmid() - Reset any private state associated with rmid


Reinette

Re: [PATCH v4 14/24] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep

[James Morse]

Hi Reinette,

On 15/06/2023 23:13, Reinette Chatre wrote:
> On 5/25/2023 11:01 AM, James Morse wrote:
>> MPAM's cache occupancy counters can take a little while to settle once
>> the monitor has been configured. The maximum settling time is described
>> to the driver via a firmware table. The value could be large enough
>> that it makes sense to sleep. To avoid exposing this to resctrl, it
>> should be hidden behind MPAM's resctrl_arch_rmid_read().
>>
>> resctrl_arch_rmid_read() may be called via IPI meaning it is unable
>> to sleep. In this case resctrl_arch_rmid_read() should return an error
>> if it needs to sleep. This will only affect MPAM platforms where
>> the cache occupancy counter isn't available immediately, nohz_full is
>> in use, and there are there are no housekeeping CPUs in the necessary
>> domain.
>>
>> There are three callers of resctrl_arch_rmid_read():
>> __mon_event_count() and __check_limbo() are both called from a
>> non-migrateable context. mon_event_read() invokes __mon_event_count()
>> using smp_call_on_cpu(), which adds work to the target CPUs workqueue.
>> rdtgroup_mutex() is held, meaning this cannot race with the resctrl
>> cpuhp callback. __check_limbo() is invoked via schedule_delayed_work_on()
>> also adds work to a per-cpu workqueue.
>>
>> The remaining call is add_rmid_to_limbo() which is called in response
>> to a user-space syscall that frees an rmid. This opportunistically
>> reads the llc occupancy counter on the current domain to see if the
>> RMID is over the dirty threshold. This has to disable preemption to
>> avoid reading the wrong domain's value. Disabling pre-emption here
>> prevents resctrl_arch_rmid_read() from sleeping.
>>
>> add_rmid_to_limbo() walks each domain, but only reads the counter
>> on one domain. If the system has more than one domain, the RMID will
>> always be added to the limbo list. If the RMIDs usage was not over the
>> threshold, it will be removed from the list when __check_limbo() runs.
>> Make this the default behaviour. Free RMIDs are always added to the
>> limbo list for each domain.
>>
>> The user visible effect of this is that a clean RMID is not available
>> for re-allocation immediately after 'rmdir()' completes, this behaviour
>> was never portable as it never happened on a machine with multiple
>> domains.
>>
>> Removing this path allows resctrl_arch_rmid_read() to sleep if its called
>> with interrupts unmasked. Document this is the expected behaviour, and
>> add a might_sleep() annotation to catch changes that won't work on arm64.


>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 6ba40495589a..fb33100e172b 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -491,7 +481,6 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>>  		set_bit(idx, d->rmid_busy_llc);
>>  		entry->busy++;
>>  	}
>> -	put_cpu();
>>  
>>  	if (entry->busy)
>>  		rmid_limbo_count++;
> 
> Would entry->busy ever be 0 after this change?

Good point - the domains list can never be empty!


>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>> index ff7452f644e4..b961936decfa 100644
>> --- a/include/linux/resctrl.h
>> +++ b/include/linux/resctrl.h
>> @@ -234,7 +234,12 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
>>   * @eventid:		eventid to read, e.g. L3 occupancy.
>>   * @val:		result of the counter read in bytes.
>>   *
>> - * Call from process context on a CPU that belongs to domain @d.
>> + * Some architectures need to sleep when first programming some of the counters.
>> + * (specifically: arm64's MPAM cache occupancy counters can return 'not ready'
>> + *  for a short period of time). Call from a non-migrateable process context on
>> + * a CPU that belongs to domain @d. e.g. use smp_call_on_cpu() or
>> + * schedule_work_on(). This function can be called with interrupts masked,
>> + * e.g. using smp_call_function_any(), but may concistently return an error.
>>   *
> 
> concistently -> consistently?
> 
>>   * Return:
>>   * 0 on success, or -EIO, -EINVAL etc on error.
>> @@ -243,6 +248,17 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>>  			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
>>  			   u64 *val);
>>  
>> +/**
>> + * resctrl_arch_rmid_read_context_check()  - warn about invalid contexts
>> + *
>> + * When built with CONFIG_DEBUG_ATOMIC_SLEEP, this function will generate a
>> + * warning when resctrl_arch_rmid_read() is called from an invalid context.
> 
> No need to say "this function" 
> Could this comment be more specific about which contexts are invalid instead of
> just referring to it as "invalid context". This seems to expect the reader to
> already know what an invalid context would be. 

I thought the implementation was enough - the comment was intended to say this does
nothing unless you select that build option. I've changed it to:
| * When built with CONFIG_DEBUG_ATOMIC_SLEEP generate a warning when
| * resctrl_arch_rmid_read() is called with preemption disabled.


>> + */
>> +static inline void resctrl_arch_rmid_read_context_check(void)
>> +{
>> +	if (!irqs_disabled())
>> +		might_sleep();
>> +}

> Could you please elaborate why the "!irqs_disabled()" is needed?

It's a question of what the interface should support.
It needs to support being called via IPI because that is going to happen on NOHZ_FULL
platforms. In this case the platforms where the MPAM code needs to sleep will have to
return an error. For folk that see this in practice: they need at least one housekeeping
CPU per domain.

Outside that the function shouldn't be called with pre-emption disabled, as that would
prevent it from sleeping, but the lockdep annotations that check for pre-emption also go
off when interrupts are masked, hence the slightly funny check.

It's documented against resctrl_arch_rmid_read():
| * Some architectures need to sleep when first programming some of the counters.
| * (specifically: arm64's MPAM cache occupancy counters can return 'not ready'
| *  for a short period of time). Call from a non-migrateable process context on
| * a CPU that belongs to domain @d. e.g. use smp_call_on_cpu() or
| * schedule_work_on(). This function can be called with interrupts masked,
| * e.g. using smp_call_function_any(), but may consistently return an error.


Thanks,

James

[PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read()

[James Morse]

Depending on the number of monitors available, Arm's MPAM may need to
allocate a monitor prior to reading the counter value. Allocating a
contended resource may involve sleeping.

add_rmid_to_limbo() calls resctrl_arch_rmid_read() for multiple domains,
the allocation should be valid for all domains.

__check_limbo() and mon_event_count() each make multiple calls to
resctrl_arch_rmid_read(), to avoid extra work on contended systems,
the allocation should be valid for multiple invocations of
resctrl_arch_rmid_read().

Add arch hooks for this allocation, which need calling before
resctrl_arch_rmid_read(). The allocated monitor is passed to
resctrl_arch_rmid_read(), then freed again afterwards. The helper
can be called on any CPU, and can sleep.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
----
Changes since v3:
 * Expanded comment.
 * Removed stray header include.
 * Reworded commit message.
 * Made ctx a void * instead of an int.
---
 arch/x86/include/asm/resctrl.h            | 11 ++++++++++
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  5 +++++
 arch/x86/kernel/cpu/resctrl/internal.h    |  1 +
 arch/x86/kernel/cpu/resctrl/monitor.c     | 26 +++++++++++++++++++----
 include/linux/resctrl.h                   |  5 ++++-
 5 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 78376c19ee6f..20729364982b 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -136,6 +136,17 @@ static inline u32 resctrl_arch_rmid_idx_encode(u32 ignored, u32 rmid)
 	return rmid;
 }
 
+/* x86 can always read an rmid, nothing needs allocating */
+struct rdt_resource;
+static inline void *resctrl_arch_mon_ctx_alloc(struct rdt_resource *r, int evtid)
+{
+	might_sleep();
+	return NULL;
+};
+
+static inline void resctrl_arch_mon_ctx_free(struct rdt_resource *r, int evtid,
+					     void *ctx) { };
+
 void resctrl_cpu_detect(struct cpuinfo_x86 *c);
 
 #else
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 6eeccad192ee..280d66fae21c 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -546,6 +546,9 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 	rr->d = d;
 	rr->val = 0;
 	rr->first = first;
+	rr->arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, evtid);
+	if (IS_ERR(rr->arch_mon_ctx))
+		return;
 
 	cpu = cpumask_any_housekeeping(&d->cpu_mask);
 
@@ -559,6 +562,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 		smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);
 	else
 		smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
+
+	resctrl_arch_mon_ctx_free(r, evtid, rr->arch_mon_ctx);
 }
 
 int rdtgroup_mondata_show(struct seq_file *m, void *arg)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 7960366b9434..a7e025cffdbc 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -136,6 +136,7 @@ struct rmid_read {
 	bool			first;
 	int			err;
 	u64			val;
+	void			*arch_mon_ctx;
 };
 
 extern bool rdt_alloc_capable;
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index fb33100e172b..6d140018358a 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -264,7 +264,7 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
 
 int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
-			   u64 *val)
+			   u64 *val, void *ignored)
 {
 	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
 	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
@@ -331,9 +331,14 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
 	struct rmid_entry *entry;
 	u32 idx, cur_idx = 1;
+	void *arch_mon_ctx;
 	bool rmid_dirty;
 	u64 val = 0;
 
+	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, QOS_L3_OCCUP_EVENT_ID);
+	if (arch_mon_ctx < 0)
+		return;
+
 	/*
 	 * Skip RMID 0 and start from RMID 1 and check all the RMIDs that
 	 * are marked as busy for occupancy < threshold. If the occupancy
@@ -347,7 +352,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 
 		entry = __rmid_entry(idx);
 		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
-					   QOS_L3_OCCUP_EVENT_ID, &val)) {
+					   QOS_L3_OCCUP_EVENT_ID, &val,
+					   arch_mon_ctx)) {
 			rmid_dirty = true;
 		} else {
 			rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
@@ -360,6 +366,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 		}
 		cur_idx = idx + 1;
 	}
+
+	resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID, arch_mon_ctx);
 }
 
 bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
@@ -539,7 +547,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
 	}
 
 	rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid, rr->evtid,
-					 &tval);
+					 &tval, rr->arch_mon_ctx);
 	if (rr->err)
 		return rr->err;
 
@@ -589,7 +597,6 @@ void mon_event_count(void *info)
 	int ret;
 
 	rdtgrp = rr->rgrp;
-
 	ret = __mon_event_count(rdtgrp->closid, rdtgrp->mon.rmid, rr);
 
 	/*
@@ -749,11 +756,21 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
 	if (is_mbm_total_enabled()) {
 		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
 		rr.val = 0;
+		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
+		if (rr.arch_mon_ctx < 0)
+			return;
+
 		__mon_event_count(closid, rmid, &rr);
+
+		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
 	}
 	if (is_mbm_local_enabled()) {
 		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
 		rr.val = 0;
+		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
+		if (rr.arch_mon_ctx < 0)
+			return;
+
 		__mon_event_count(closid, rmid, &rr);
 
 		/*
@@ -763,6 +780,7 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
 		 */
 		if (is_mba_sc(NULL))
 			mbm_bw_count(closid, rmid, &rr);
+		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
 	}
 }
 
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index b961936decfa..0dcb5cfde609 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -233,6 +233,9 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
  * @rmid:		rmid of the counter to read.
  * @eventid:		eventid to read, e.g. L3 occupancy.
  * @val:		result of the counter read in bytes.
+ * @arch_mon_ctx:	An architecture specific value from
+ *			resctrl_arch_mon_ctx_alloc(), for MPAM this identifies
+ *			the hardware monitor allocated for this read request.
  *
  * Some architectures need to sleep when first programming some of the counters.
  * (specifically: arm64's MPAM cache occupancy counters can return 'not ready'
@@ -246,7 +249,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
  */
 int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
-			   u64 *val);
+			   u64 *val, void *arch_mon_ctx);
 
 /**
  * resctrl_arch_rmid_read_context_check()  - warn about invalid contexts
-- 
2.39.2

RE: [PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read()

[Shaopeng Tan (Fujitsu)]

Hello James,


> Depending on the number of monitors available, Arm's MPAM may need to
> allocate a monitor prior to reading the counter value. Allocating a contended
> resource may involve sleeping.
> 
> add_rmid_to_limbo() calls resctrl_arch_rmid_read() for multiple domains, the
> allocation should be valid for all domains.
> 
> __check_limbo() and mon_event_count() each make multiple calls to
> resctrl_arch_rmid_read(), to avoid extra work on contended systems, the
> allocation should be valid for multiple invocations of resctrl_arch_rmid_read().
> 
> Add arch hooks for this allocation, which need calling before
> resctrl_arch_rmid_read(). The allocated monitor is passed to
> resctrl_arch_rmid_read(), then freed again afterwards. The helper can be
> called on any CPU, and can sleep.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ----
> Changes since v3:
>  * Expanded comment.
>  * Removed stray header include.
>  * Reworded commit message.
>  * Made ctx a void * instead of an int.
> ---
>  arch/x86/include/asm/resctrl.h            | 11 ++++++++++
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  5 +++++
>  arch/x86/kernel/cpu/resctrl/internal.h    |  1 +
>  arch/x86/kernel/cpu/resctrl/monitor.c     | 26
> +++++++++++++++++++----
>  include/linux/resctrl.h                   |  5 ++++-
>  5 files changed, 43 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index 78376c19ee6f..20729364982b 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -136,6 +136,17 @@ static inline u32 resctrl_arch_rmid_idx_encode(u32
> ignored, u32 rmid)
>  	return rmid;
>  }
> 
> +/* x86 can always read an rmid, nothing needs allocating */ struct
> +rdt_resource; static inline void *resctrl_arch_mon_ctx_alloc(struct
> +rdt_resource *r, int evtid) {
> +	might_sleep();
> +	return NULL;
> +};
> +
> +static inline void resctrl_arch_mon_ctx_free(struct rdt_resource *r, int evtid,
> +					     void *ctx) { };
> +
>  void resctrl_cpu_detect(struct cpuinfo_x86 *c);
> 
>  #else
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index 6eeccad192ee..280d66fae21c 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -546,6 +546,9 @@ void mon_event_read(struct rmid_read *rr, struct
> rdt_resource *r,
>  	rr->d = d;
>  	rr->val = 0;
>  	rr->first = first;
> +	rr->arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, evtid);
> +	if (IS_ERR(rr->arch_mon_ctx))
> +		return;
> 
>  	cpu = cpumask_any_housekeeping(&d->cpu_mask);
> 
> @@ -559,6 +562,8 @@ void mon_event_read(struct rmid_read *rr, struct
> rdt_resource *r,
>  		smp_call_function_any(&d->cpu_mask, mon_event_count, rr,
> 1);
>  	else
>  		smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
> +
> +	resctrl_arch_mon_ctx_free(r, evtid, rr->arch_mon_ctx);
>  }
> 
>  int rdtgroup_mondata_show(struct seq_file *m, void *arg) diff --git
> a/arch/x86/kernel/cpu/resctrl/internal.h
> b/arch/x86/kernel/cpu/resctrl/internal.h
> index 7960366b9434..a7e025cffdbc 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -136,6 +136,7 @@ struct rmid_read {
>  	bool			first;
>  	int			err;
>  	u64			val;
> +	void			*arch_mon_ctx;
>  };
> 
>  extern bool rdt_alloc_capable;
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index fb33100e172b..6d140018358a 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -264,7 +264,7 @@ static u64 mbm_overflow_count(u64 prev_msr, u64
> cur_msr, unsigned int width)
> 
>  int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>  			   u32 closid, u32 rmid, enum resctrl_event_id
> eventid,
> -			   u64 *val)
> +			   u64 *val, void *ignored)
>  {
>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>  	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d); @@
> -331,9 +331,14 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>  	struct rmid_entry *entry;
>  	u32 idx, cur_idx = 1;
> +	void *arch_mon_ctx;
>  	bool rmid_dirty;
>  	u64 val = 0;
> 
> +	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r,
> QOS_L3_OCCUP_EVENT_ID);
> +	if (arch_mon_ctx < 0)
> +		return;
> +

Would it be better to use IS_ERR() macro?

>  	/*
>  	 * Skip RMID 0 and start from RMID 1 and check all the RMIDs that
>  	 * are marked as busy for occupancy < threshold. If the occupancy @@
> -347,7 +352,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
> 
>  		entry = __rmid_entry(idx);
>  		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
> -					   QOS_L3_OCCUP_EVENT_ID,
> &val)) {
> +					   QOS_L3_OCCUP_EVENT_ID,
> &val,
> +					   arch_mon_ctx)) {
>  			rmid_dirty = true;
>  		} else {
>  			rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
> @@ -360,6 +366,8 @@ void __check_limbo(struct rdt_domain *d, bool
> force_free)
>  		}
>  		cur_idx = idx + 1;
>  	}
> +
> +	resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID,
> arch_mon_ctx);
>  }
> 
>  bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d) @@ -539,7
> +547,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct
> rmid_read *rr)
>  	}
> 
>  	rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid, rr->evtid,
> -					 &tval);
> +					 &tval, rr->arch_mon_ctx);
>  	if (rr->err)
>  		return rr->err;
> 
> @@ -589,7 +597,6 @@ void mon_event_count(void *info)
>  	int ret;
> 
>  	rdtgrp = rr->rgrp;
> -
>  	ret = __mon_event_count(rdtgrp->closid, rdtgrp->mon.rmid, rr);
> 
>  	/*
> @@ -749,11 +756,21 @@ static void mbm_update(struct rdt_resource *r, struct
> rdt_domain *d,
>  	if (is_mbm_total_enabled()) {
>  		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
>  		rr.val = 0;
> +		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> +		if (rr.arch_mon_ctx < 0)
> +			return;
> +
Same here.

>  		__mon_event_count(closid, rmid, &rr);
> +
> +		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
>  	}
>  	if (is_mbm_local_enabled()) {
>  		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
>  		rr.val = 0;
> +		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> +		if (rr.arch_mon_ctx < 0)
> +			return;
> +
Same here.

Best regards,
Shaopeng TAN

Re: [PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read()

[James Morse]

Hi Shaopeng TAN,

On 12/06/2023 06:39, Shaopeng Tan (Fujitsu) wrote:
>> Depending on the number of monitors available, Arm's MPAM may need to
>> allocate a monitor prior to reading the counter value. Allocating a contended
>> resource may involve sleeping.
>>
>> add_rmid_to_limbo() calls resctrl_arch_rmid_read() for multiple domains, the
>> allocation should be valid for all domains.
>>
>> __check_limbo() and mon_event_count() each make multiple calls to
>> resctrl_arch_rmid_read(), to avoid extra work on contended systems, the
>> allocation should be valid for multiple invocations of resctrl_arch_rmid_read().
>>
>> Add arch hooks for this allocation, which need calling before
>> resctrl_arch_rmid_read(). The allocated monitor is passed to
>> resctrl_arch_rmid_read(), then freed again afterwards. The helper can be
>> called on any CPU, and can sleep.

>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index fb33100e172b..6d140018358a 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c

>> @@ -331,9 +331,14 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>>  	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>>  	struct rmid_entry *entry;
>>  	u32 idx, cur_idx = 1;
>> +	void *arch_mon_ctx;
>>  	bool rmid_dirty;
>>  	u64 val = 0;
>>
>> +	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r,
>> QOS_L3_OCCUP_EVENT_ID);
>> +	if (arch_mon_ctx < 0)
>> +		return;
>> +
> 
> Would it be better to use IS_ERR() macro?

Yup, much more readable!


Thanks,

James

Re: [PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read()

[Reinette Chatre]

Hi James,

On 5/25/2023 11:02 AM, James Morse wrote:
> Depending on the number of monitors available, Arm's MPAM may need to
> allocate a monitor prior to reading the counter value. Allocating a
> contended resource may involve sleeping.
> 
> add_rmid_to_limbo() calls resctrl_arch_rmid_read() for multiple domains,
> the allocation should be valid for all domains.
> 
> __check_limbo() and mon_event_count() each make multiple calls to
> resctrl_arch_rmid_read(), to avoid extra work on contended systems,
> the allocation should be valid for multiple invocations of
> resctrl_arch_rmid_read().
> 
> Add arch hooks for this allocation, which need calling before
> resctrl_arch_rmid_read(). The allocated monitor is passed to
> resctrl_arch_rmid_read(), then freed again afterwards. The helper
> can be called on any CPU, and can sleep.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ----

Note the extra "-" 

> Changes since v3:
>  * Expanded comment.
>  * Removed stray header include.
>  * Reworded commit message.
>  * Made ctx a void * instead of an int.
> ---

...

> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index fb33100e172b..6d140018358a 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -264,7 +264,7 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
>  
>  int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>  			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
> -			   u64 *val)
> +			   u64 *val, void *ignored)
>  {
>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>  	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
> @@ -331,9 +331,14 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>  	struct rmid_entry *entry;
>  	u32 idx, cur_idx = 1;
> +	void *arch_mon_ctx;
>  	bool rmid_dirty;
>  	u64 val = 0;
>  
> +	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, QOS_L3_OCCUP_EVENT_ID);
> +	if (arch_mon_ctx < 0)
> +		return;
> +

It seems that not all has adapted to the new type.

>  	/*
>  	 * Skip RMID 0 and start from RMID 1 and check all the RMIDs that
>  	 * are marked as busy for occupancy < threshold. If the occupancy
> @@ -347,7 +352,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  
>  		entry = __rmid_entry(idx);
>  		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
> -					   QOS_L3_OCCUP_EVENT_ID, &val)) {
> +					   QOS_L3_OCCUP_EVENT_ID, &val,
> +					   arch_mon_ctx)) {
>  			rmid_dirty = true;
>  		} else {
>  			rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
> @@ -360,6 +366,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>  		}
>  		cur_idx = idx + 1;
>  	}
> +
> +	resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID, arch_mon_ctx);
>  }
>  
>  bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
> @@ -539,7 +547,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
>  	}
>  
>  	rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid, rr->evtid,
> -					 &tval);
> +					 &tval, rr->arch_mon_ctx);
>  	if (rr->err)
>  		return rr->err;
>  
> @@ -589,7 +597,6 @@ void mon_event_count(void *info)
>  	int ret;
>  
>  	rdtgrp = rr->rgrp;
> -
>  	ret = __mon_event_count(rdtgrp->closid, rdtgrp->mon.rmid, rr);
>  

Stray change.

>  	/*


Reinette

[PATCH v4 16/24] x86/resctrl: Make resctrl_mounted checks explicit

[James Morse]

The rdt_enable_key is switched when resctrl is mounted, and used to
prevent a second mount of the filesystem. It also enables the
architecture's context switch code.

This requires another architecture to have the same set of static-keys,
as resctrl depends on them too. The existing users of these static-keys
are implicitly also checking if the filesystem is mounted.

Make the resctrl_mounted checks explicit: resctrl can keep track of
whether it has been mounted once. This doesn't need to be combined with
whether the arch code is context switching the CLOSID.

rdt_mon_enable_key is never used just to test that resctrl is mounted,
but does also have this implication. Add a resctrl_mounted to all uses
of rdt_mon_enable_key. This will allow rdt_mon_enable_key to be swapped
with a helper in a subsequent patch.

This will allow the static-key changing to be moved behind resctrl_arch_
calls.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>

----
Changse since v3:
 * Removed a newline.
 * Rephrased commit message
---
 arch/x86/kernel/cpu/resctrl/internal.h |  1 +
 arch/x86/kernel/cpu/resctrl/monitor.c  | 12 ++++++++++--
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 21 +++++++++++++++------
 3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index a7e025cffdbc..67cabda6fd4d 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -143,6 +143,7 @@ extern bool rdt_alloc_capable;
 extern bool rdt_mon_capable;
 extern unsigned int rdt_mon_features;
 extern struct list_head resctrl_schema_all;
+extern bool resctrl_mounted;
 
 enum rdt_group_type {
 	RDTCTRL_GROUP = 0,
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 6d140018358a..da5a86c95142 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -832,7 +832,11 @@ void mbm_handle_overflow(struct work_struct *work)
 
 	mutex_lock(&rdtgroup_mutex);
 
-	if (!static_branch_likely(&rdt_mon_enable_key))
+	/*
+	 * If the filesystem has been unmounted this work no longer needs to
+	 * run.
+	 */
+	if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
 		goto out_unlock;
 
 	r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
@@ -865,7 +869,11 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 	unsigned long delay = msecs_to_jiffies(delay_ms);
 	int cpu;
 
-	if (!static_branch_likely(&rdt_mon_enable_key))
+	/*
+	 * When a domain comes online there is no guarantee the filesystem is
+	 * mounted. If not, there is no need to catch counter overflow.
+	 */
+	if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
 		return;
 	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
 	dom->mbm_work_cpu = cpu;
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index f2bb3e09ed13..47bb3ab775fc 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -42,6 +42,9 @@ LIST_HEAD(rdt_all_groups);
 /* list of entries for the schemata file */
 LIST_HEAD(resctrl_schema_all);
 
+/* The filesystem can only be mounted once. */
+bool resctrl_mounted;
+
 /* Kernel fs node for "info" directory under root */
 static struct kernfs_node *kn_info;
 
@@ -815,7 +818,7 @@ int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
 	mutex_lock(&rdtgroup_mutex);
 
 	/* Return empty if resctrl has not been mounted. */
-	if (!static_branch_unlikely(&rdt_enable_key)) {
+	if (!resctrl_mounted) {
 		seq_puts(s, "res:\nmon:\n");
 		goto unlock;
 	}
@@ -2482,7 +2485,7 @@ static int rdt_get_tree(struct fs_context *fc)
 	/*
 	 * resctrl file system can only be mounted once.
 	 */
-	if (static_branch_unlikely(&rdt_enable_key)) {
+	if (resctrl_mounted) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -2530,8 +2533,10 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (rdt_mon_capable)
 		static_branch_enable_cpuslocked(&rdt_mon_enable_key);
 
-	if (rdt_alloc_capable || rdt_mon_capable)
+	if (rdt_alloc_capable || rdt_mon_capable) {
 		static_branch_enable_cpuslocked(&rdt_enable_key);
+		resctrl_mounted = true;
+	}
 
 	if (is_mbm_enabled()) {
 		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
@@ -2802,6 +2807,7 @@ static void rdt_kill_sb(struct super_block *sb)
 	static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
 	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
 	static_branch_disable_cpuslocked(&rdt_enable_key);
+	resctrl_mounted = false;
 	kernfs_kill_sb(sb);
 	mutex_unlock(&rdtgroup_mutex);
 	cpus_read_unlock();
@@ -3633,7 +3639,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
 	 * If resctrl is mounted, remove all the
 	 * per domain monitor data directories.
 	 */
-	if (static_branch_unlikely(&rdt_mon_enable_key))
+	if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
 		rmdir_mondata_subdir_allrdtgrp(r, d->id);
 
 	if (is_mbm_enabled())
@@ -3710,8 +3716,11 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
 	if (is_llc_occupancy_enabled())
 		INIT_DELAYED_WORK(&d->cqm_limbo, cqm_handle_limbo);
 
-	/* If resctrl is mounted, add per domain monitor data directories. */
-	if (static_branch_unlikely(&rdt_mon_enable_key))
+	/*
+	 * If the filesystem is not mounted, creating directories is deferred
+	 * until mount time by rdt_get_tree() calling mkdir_mondata_all().
+	 */
+	if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
 		mkdir_mondata_subdir_allrdtgrp(r, d);
 
 	return 0;
-- 
2.39.2

Re: [PATCH v4 16/24] x86/resctrl: Make resctrl_mounted checks explicit

[Reinette Chatre]

Hi James,

On 5/25/2023 11:02 AM, James Morse wrote:

...

> @@ -3710,8 +3716,11 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>  	if (is_llc_occupancy_enabled())
>  		INIT_DELAYED_WORK(&d->cqm_limbo, cqm_handle_limbo);
>  
> -	/* If resctrl is mounted, add per domain monitor data directories. */
> -	if (static_branch_unlikely(&rdt_mon_enable_key))
> +	/*
> +	 * If the filesystem is not mounted, creating directories is deferred
> +	 * until mount time by rdt_get_tree() calling mkdir_mondata_all().
> +	 */

I do not think that this new comment captures this work. This code is when a new
domain comes online and directories need to be created in all the existing
resource groups. This includes the default resource group as well as those created
after resctrl was mounted. The new comment states that this is "deferred until mount
time by rdt_get_tree() calling mkdir_mondata_all()" - but I do not think that is 
accurate since the reader is point to the directories created just for the default
resource group.
Perhaps something like:

	/*
	 * If the filesystem is not mounted then only the default resource group
	 * exists. Creation of its directories is deferred until mount time
	 * by rdt_get_tree() calling mkdir_mondata_all().
	 */

I do think that the comment explaining what the code does is helpful though.
Can you please also keep the comment about what is done in the case when resctrl
is indeed mounted?


> +	if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
>  		mkdir_mondata_subdir_allrdtgrp(r, d);
>  
>  	return 0;


Reinette

[PATCH v4 17/24] x86/resctrl: Move alloc/mon static keys into helpers

[James Morse]

resctrl enables three static keys depending on the features it has enabled.
Another architecture's context switch code may look different, any
static keys that control it should be buried behind helpers.

Move the alloc/mon logic into arch-specific helpers as a preparatory step
for making the rdt_enable_key's status something the arch code decides.

This means other architectures don't have to mirror the static keys.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/include/asm/resctrl.h         | 20 ++++++++++++++++++++
 arch/x86/kernel/cpu/resctrl/internal.h |  5 -----
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  8 ++++----
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 20729364982b..83ec2b5791f0 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -42,6 +42,26 @@ DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
 DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
 DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
 
+static inline void resctrl_arch_enable_alloc(void)
+{
+	static_branch_enable_cpuslocked(&rdt_alloc_enable_key);
+}
+
+static inline void resctrl_arch_disable_alloc(void)
+{
+	static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
+}
+
+static inline void resctrl_arch_enable_mon(void)
+{
+	static_branch_enable_cpuslocked(&rdt_mon_enable_key);
+}
+
+static inline void resctrl_arch_disable_mon(void)
+{
+	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
+}
+
 /*
  * __resctrl_sched_in() - Writes the task's CLOSid/RMID to IA32_PQR_MSR
  *
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 67cabda6fd4d..8660210ae958 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -93,9 +93,6 @@ static inline struct rdt_fs_context *rdt_fc2context(struct fs_context *fc)
 	return container_of(kfc, struct rdt_fs_context, kfc);
 }
 
-DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
-DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
-
 /**
  * struct mon_evt - Entry in the event list of a resource
  * @evtid:		event id
@@ -453,8 +450,6 @@ extern struct mutex rdtgroup_mutex;
 
 extern struct rdt_hw_resource rdt_resources_all[];
 extern struct rdtgroup rdtgroup_default;
-DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
-
 extern struct dentry *debugfs_resctrl;
 
 enum resctrl_res_level {
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 47bb3ab775fc..9e65248908d6 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2529,9 +2529,9 @@ static int rdt_get_tree(struct fs_context *fc)
 		goto out_psl;
 
 	if (rdt_alloc_capable)
-		static_branch_enable_cpuslocked(&rdt_alloc_enable_key);
+		resctrl_arch_enable_alloc();
 	if (rdt_mon_capable)
-		static_branch_enable_cpuslocked(&rdt_mon_enable_key);
+		resctrl_arch_enable_mon();
 
 	if (rdt_alloc_capable || rdt_mon_capable) {
 		static_branch_enable_cpuslocked(&rdt_enable_key);
@@ -2804,8 +2804,8 @@ static void rdt_kill_sb(struct super_block *sb)
 	rdt_pseudo_lock_release();
 	rdtgroup_default.mode = RDT_MODE_SHAREABLE;
 	schemata_list_destroy();
-	static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
-	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
+	resctrl_arch_disable_alloc();
+	resctrl_arch_disable_mon();
 	static_branch_disable_cpuslocked(&rdt_enable_key);
 	resctrl_mounted = false;
 	kernfs_kill_sb(sb);
-- 
2.39.2

[PATCH v4 18/24] x86/resctrl: Make rdt_enable_key the arch's decision to switch

[James Morse]

rdt_enable_key is switched when resctrl is mounted. It was also previously
used to prevent a second mount of the filesystem.

Any other architecture that wants to support resctrl has to provide
identical static keys.

Now that there are helpers for enabling and disabling the alloc/mon keys,
resctrl doesn't need to switch this extra key, it can be done by the arch
code. Use the static-key increment and decrement helpers, and change
resctrl to ensure the calls are balanced.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/include/asm/resctrl.h         |  4 ++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 11 +++++------
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 83ec2b5791f0..839b701cf7bd 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -45,21 +45,25 @@ DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
 static inline void resctrl_arch_enable_alloc(void)
 {
 	static_branch_enable_cpuslocked(&rdt_alloc_enable_key);
+	static_branch_inc_cpuslocked(&rdt_enable_key);
 }
 
 static inline void resctrl_arch_disable_alloc(void)
 {
 	static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
+	static_branch_dec_cpuslocked(&rdt_enable_key);
 }
 
 static inline void resctrl_arch_enable_mon(void)
 {
 	static_branch_enable_cpuslocked(&rdt_mon_enable_key);
+	static_branch_inc_cpuslocked(&rdt_enable_key);
 }
 
 static inline void resctrl_arch_disable_mon(void)
 {
 	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
+	static_branch_dec_cpuslocked(&rdt_enable_key);
 }
 
 /*
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 9e65248908d6..501b68b95aef 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2533,10 +2533,8 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (rdt_mon_capable)
 		resctrl_arch_enable_mon();
 
-	if (rdt_alloc_capable || rdt_mon_capable) {
-		static_branch_enable_cpuslocked(&rdt_enable_key);
+	if (rdt_alloc_capable || rdt_mon_capable)
 		resctrl_mounted = true;
-	}
 
 	if (is_mbm_enabled()) {
 		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
@@ -2804,9 +2802,10 @@ static void rdt_kill_sb(struct super_block *sb)
 	rdt_pseudo_lock_release();
 	rdtgroup_default.mode = RDT_MODE_SHAREABLE;
 	schemata_list_destroy();
-	resctrl_arch_disable_alloc();
-	resctrl_arch_disable_mon();
-	static_branch_disable_cpuslocked(&rdt_enable_key);
+	if (rdt_alloc_capable)
+		resctrl_arch_disable_alloc();
+	if (rdt_mon_capable)
+		resctrl_arch_disable_mon();
 	resctrl_mounted = false;
 	kernfs_kill_sb(sb);
 	mutex_unlock(&rdtgroup_mutex);
-- 
2.39.2

[PATCH v4 19/24] x86/resctrl: Add helpers for system wide mon/alloc capable

[James Morse]

resctrl reads rdt_alloc_capable or rdt_mon_capable to determine
whether any of the resources support the corresponding features.
resctrl also uses the static-keys that affect the architecture's
context-switch code to determine the same thing.

This forces another architecture to have the same static-keys.

As the static-key is enabled based on the capable flag, and none of
the filesystem uses of these are in the scheduler path, move the
capable flags behind helpers, and use these in the filesystem
code instead of the static-key.

After this change, only the architecture code manages and uses
the static-keys to ensure __resctrl_sched_in() does not need
runtime checks.

This avoids multiple architectures having to define the same
static-keys.

Cases where the static-key implicitly tested if the resctrl
filesystem was mounted all have an explicit check added by a
previous patch.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>

---
Changes since v1:
 * Added missing conversion in mkdir_rdt_prepare_rmid_free()

Changes since v3:
 * Expanded the commit message.
---
 arch/x86/include/asm/resctrl.h            | 13 +++++++++
 arch/x86/kernel/cpu/resctrl/internal.h    |  2 --
 arch/x86/kernel/cpu/resctrl/monitor.c     |  4 +--
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  6 ++--
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 34 +++++++++++------------
 5 files changed, 35 insertions(+), 24 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 839b701cf7bd..8acab1112255 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -38,10 +38,18 @@ struct resctrl_pqr_state {
 
 DECLARE_PER_CPU(struct resctrl_pqr_state, pqr_state);
 
+extern bool rdt_alloc_capable;
+extern bool rdt_mon_capable;
+
 DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
 DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
 DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
 
+static inline bool resctrl_arch_alloc_capable(void)
+{
+	return rdt_alloc_capable;
+}
+
 static inline void resctrl_arch_enable_alloc(void)
 {
 	static_branch_enable_cpuslocked(&rdt_alloc_enable_key);
@@ -54,6 +62,11 @@ static inline void resctrl_arch_disable_alloc(void)
 	static_branch_dec_cpuslocked(&rdt_enable_key);
 }
 
+static inline bool resctrl_arch_mon_capable(void)
+{
+	return rdt_mon_capable;
+}
+
 static inline void resctrl_arch_enable_mon(void)
 {
 	static_branch_enable_cpuslocked(&rdt_mon_enable_key);
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 8660210ae958..021a8956518c 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -136,8 +136,6 @@ struct rmid_read {
 	void			*arch_mon_ctx;
 };
 
-extern bool rdt_alloc_capable;
-extern bool rdt_mon_capable;
 extern unsigned int rdt_mon_features;
 extern struct list_head resctrl_schema_all;
 extern bool resctrl_mounted;
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index da5a86c95142..ced933694f60 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -836,7 +836,7 @@ void mbm_handle_overflow(struct work_struct *work)
 	 * If the filesystem has been unmounted this work no longer needs to
 	 * run.
 	 */
-	if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
+	if (!resctrl_mounted || !resctrl_arch_mon_capable())
 		goto out_unlock;
 
 	r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
@@ -873,7 +873,7 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 	 * When a domain comes online there is no guarantee the filesystem is
 	 * mounted. If not, there is no need to catch counter overflow.
 	 */
-	if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
+	if (!resctrl_mounted || !resctrl_arch_mon_capable())
 		return;
 	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
 	dom->mbm_work_cpu = cpu;
diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index 5ebd6e54c7f2..460421051abf 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -567,7 +567,7 @@ static int rdtgroup_locksetup_user_restrict(struct rdtgroup *rdtgrp)
 	if (ret)
 		goto err_cpus;
 
-	if (rdt_mon_capable) {
+	if (resctrl_arch_mon_capable()) {
 		ret = rdtgroup_kn_mode_restrict(rdtgrp, "mon_groups");
 		if (ret)
 			goto err_cpus_list;
@@ -614,7 +614,7 @@ static int rdtgroup_locksetup_user_restore(struct rdtgroup *rdtgrp)
 	if (ret)
 		goto err_cpus;
 
-	if (rdt_mon_capable) {
+	if (resctrl_arch_mon_capable()) {
 		ret = rdtgroup_kn_mode_restore(rdtgrp, "mon_groups", 0777);
 		if (ret)
 			goto err_cpus_list;
@@ -762,7 +762,7 @@ int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp)
 {
 	int ret;
 
-	if (rdt_mon_capable) {
+	if (resctrl_arch_mon_capable()) {
 		ret = alloc_rmid(rdtgrp->closid);
 		if (ret < 0) {
 			rdt_last_cmd_puts("Out of RMIDs\n");
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 501b68b95aef..5330c0bdeffc 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -630,13 +630,13 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 
 static bool is_closid_match(struct task_struct *t, struct rdtgroup *r)
 {
-	return (rdt_alloc_capable && (r->type == RDTCTRL_GROUP) &&
+	return (resctrl_arch_alloc_capable() && (r->type == RDTCTRL_GROUP) &&
 		resctrl_arch_match_closid(t, r->closid));
 }
 
 static bool is_rmid_match(struct task_struct *t, struct rdtgroup *r)
 {
-	return (rdt_mon_capable && (r->type == RDTMON_GROUP) &&
+	return (resctrl_arch_mon_capable() && (r->type == RDTMON_GROUP) &&
 		resctrl_arch_match_rmid(t, r->mon.parent->closid,
 					r->mon.rmid));
 }
@@ -2506,7 +2506,7 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (ret < 0)
 		goto out_schemata_free;
 
-	if (rdt_mon_capable) {
+	if (resctrl_arch_mon_capable()) {
 		ret = mongroup_create_dir(rdtgroup_default.kn,
 					  &rdtgroup_default, "mon_groups",
 					  &kn_mongrp);
@@ -2528,12 +2528,12 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (ret < 0)
 		goto out_psl;
 
-	if (rdt_alloc_capable)
+	if (resctrl_arch_alloc_capable())
 		resctrl_arch_enable_alloc();
-	if (rdt_mon_capable)
+	if (resctrl_arch_mon_capable())
 		resctrl_arch_enable_mon();
 
-	if (rdt_alloc_capable || rdt_mon_capable)
+	if (resctrl_arch_alloc_capable() || resctrl_arch_mon_capable())
 		resctrl_mounted = true;
 
 	if (is_mbm_enabled()) {
@@ -2547,10 +2547,10 @@ static int rdt_get_tree(struct fs_context *fc)
 out_psl:
 	rdt_pseudo_lock_release();
 out_mondata:
-	if (rdt_mon_capable)
+	if (resctrl_arch_mon_capable())
 		kernfs_remove(kn_mondata);
 out_mongrp:
-	if (rdt_mon_capable)
+	if (resctrl_arch_mon_capable())
 		kernfs_remove(kn_mongrp);
 out_info:
 	kernfs_remove(kn_info);
@@ -2802,9 +2802,9 @@ static void rdt_kill_sb(struct super_block *sb)
 	rdt_pseudo_lock_release();
 	rdtgroup_default.mode = RDT_MODE_SHAREABLE;
 	schemata_list_destroy();
-	if (rdt_alloc_capable)
+	if (resctrl_arch_alloc_capable())
 		resctrl_arch_disable_alloc();
-	if (rdt_mon_capable)
+	if (resctrl_arch_mon_capable())
 		resctrl_arch_disable_mon();
 	resctrl_mounted = false;
 	kernfs_kill_sb(sb);
@@ -3184,7 +3184,7 @@ static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
 {
 	int ret;
 
-	if (!rdt_mon_capable)
+	if (!resctrl_arch_mon_capable())
 		return 0;
 
 	ret = alloc_rmid(rdtgrp->closid);
@@ -3206,7 +3206,7 @@ static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
 
 static void mkdir_rdt_prepare_rmid_free(struct rdtgroup *rgrp)
 {
-	if (rdt_mon_capable)
+	if (resctrl_arch_mon_capable())
 		free_rmid(rgrp->closid, rgrp->mon.rmid);
 }
 
@@ -3372,7 +3372,7 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
 
 	list_add(&rdtgrp->rdtgroup_list, &rdt_all_groups);
 
-	if (rdt_mon_capable) {
+	if (resctrl_arch_mon_capable()) {
 		/*
 		 * Create an empty mon_groups directory to hold the subset
 		 * of tasks and cpus to monitor.
@@ -3427,14 +3427,14 @@ static int rdtgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 	 * allocation is supported, add a control and monitoring
 	 * subdirectory
 	 */
-	if (rdt_alloc_capable && parent_kn == rdtgroup_default.kn)
+	if (resctrl_arch_alloc_capable() && parent_kn == rdtgroup_default.kn)
 		return rdtgroup_mkdir_ctrl_mon(parent_kn, name, mode);
 
 	/*
 	 * If RDT monitoring is supported and the parent directory is a valid
 	 * "mon_groups" directory, add a monitoring subdirectory.
 	 */
-	if (rdt_mon_capable && is_mon_groups(parent_kn, name))
+	if (resctrl_arch_mon_capable() && is_mon_groups(parent_kn, name))
 		return rdtgroup_mkdir_mon(parent_kn, name, mode);
 
 	return -EPERM;
@@ -3638,7 +3638,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
 	 * If resctrl is mounted, remove all the
 	 * per domain monitor data directories.
 	 */
-	if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
+	if (resctrl_mounted && resctrl_arch_mon_capable())
 		rmdir_mondata_subdir_allrdtgrp(r, d->id);
 
 	if (is_mbm_enabled())
@@ -3719,7 +3719,7 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
 	 * If the filesystem is not mounted, creating directories is deferred
 	 * until mount time by rdt_get_tree() calling mkdir_mondata_all().
 	 */
-	if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
+	if (resctrl_mounted && resctrl_arch_mon_capable())
 		mkdir_mondata_subdir_allrdtgrp(r, d);
 
 	return 0;
-- 
2.39.2

[PATCH v4 20/24] x86/resctrl: Add cpu online callback for resctrl work

[James Morse]

The resctrl architecture specific code may need to create a domain when
a CPU comes online, it also needs to reset the CPUs PQR_ASSOC register.
The resctrl filesystem code needs to update the rdtgroup_default cpu
mask when cpus are brought online.

Currently this is all done in one function, resctrl_online_cpu().
This will need to be split into architecture and filesystem parts
before resctrl can be moved to /fs/.

Pull the rdtgroup_default update work out as a filesystem specific
cpu_online helper. resctrl_online_cpu() is the obvious name for this,
which means the version in core.c needs renaming.

resctrl_online_cpu() is called by the arch code once it has done the
work to add the new cpu to any domains.

In future patches, resctrl_online_cpu() will take the rdtgroup_mutex
itself.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v3:
 * Renamed err to ret
---
 arch/x86/kernel/cpu/resctrl/core.c     | 11 ++++++-----
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 10 ++++++++++
 include/linux/resctrl.h                |  1 +
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 4bea032d072e..e00f3542e60e 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -603,19 +603,20 @@ static void clear_closid_rmid(int cpu)
 	wrmsr(MSR_IA32_PQR_ASSOC, 0, RESCTRL_RESERVED_CLOSID);
 }
 
-static int resctrl_online_cpu(unsigned int cpu)
+static int resctrl_arch_online_cpu(unsigned int cpu)
 {
 	struct rdt_resource *r;
+	int ret;
 
 	mutex_lock(&rdtgroup_mutex);
 	for_each_capable_rdt_resource(r)
 		domain_add_cpu(cpu, r);
-	/* The cpu is set in default rdtgroup after online. */
-	cpumask_set_cpu(cpu, &rdtgroup_default.cpu_mask);
 	clear_closid_rmid(cpu);
+
+	ret = resctrl_online_cpu(cpu);
 	mutex_unlock(&rdtgroup_mutex);
 
-	return 0;
+	return ret;
 }
 
 static void clear_childcpus(struct rdtgroup *r, unsigned int cpu)
@@ -965,7 +966,7 @@ static int __init resctrl_late_init(void)
 
 	state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				  "x86/resctrl/cat:online:",
-				  resctrl_online_cpu, resctrl_offline_cpu);
+				  resctrl_arch_online_cpu, resctrl_offline_cpu);
 	if (state < 0)
 		return state;
 
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 5330c0bdeffc..7c3de5ea0482 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3725,6 +3725,16 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
 	return 0;
 }
 
+int resctrl_online_cpu(unsigned int cpu)
+{
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	/* The cpu is set in default rdtgroup after online. */
+	cpumask_set_cpu(cpu, &rdtgroup_default.cpu_mask);
+
+	return 0;
+}
+
 /*
  * rdtgroup_init - rdtgroup initialization
  *
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 0dcb5cfde609..ecd41762d61a 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -222,6 +222,7 @@ u32 resctrl_arch_get_config(struct rdt_resource *r, struct rdt_domain *d,
 			    u32 closid, enum resctrl_conf_type type);
 int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d);
 void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
+int resctrl_online_cpu(unsigned int cpu);
 
 /**
  * resctrl_arch_rmid_read() - Read the eventid counter corresponding to rmid
-- 
2.39.2

Re: [PATCH v4 20/24] x86/resctrl: Add cpu online callback for resctrl work

[Reinette Chatre]

Hi James,

On 5/25/2023 11:02 AM, James Morse wrote:
> The resctrl architecture specific code may need to create a domain when
> a CPU comes online, it also needs to reset the CPUs PQR_ASSOC register.
> The resctrl filesystem code needs to update the rdtgroup_default cpu
> mask when cpus are brought online.

CPU mask when CPUs

> 
> Currently this is all done in one function, resctrl_online_cpu().
> This will need to be split into architecture and filesystem parts
> before resctrl can be moved to /fs/.
> 
> Pull the rdtgroup_default update work out as a filesystem specific
> cpu_online helper. resctrl_online_cpu() is the obvious name for this,
> which means the version in core.c needs renaming.
> 
> resctrl_online_cpu() is called by the arch code once it has done the
> work to add the new cpu to any domains.

CPU

> 
> In future patches, resctrl_online_cpu() will take the rdtgroup_mutex
> itself.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v3:
>  * Renamed err to ret
> ---
>  arch/x86/kernel/cpu/resctrl/core.c     | 11 ++++++-----
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 10 ++++++++++
>  include/linux/resctrl.h                |  1 +
>  3 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 4bea032d072e..e00f3542e60e 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -603,19 +603,20 @@ static void clear_closid_rmid(int cpu)
>  	wrmsr(MSR_IA32_PQR_ASSOC, 0, RESCTRL_RESERVED_CLOSID);
>  }
>  
> -static int resctrl_online_cpu(unsigned int cpu)
> +static int resctrl_arch_online_cpu(unsigned int cpu)
>  {
>  	struct rdt_resource *r;
> +	int ret;
>  
>  	mutex_lock(&rdtgroup_mutex);
>  	for_each_capable_rdt_resource(r)
>  		domain_add_cpu(cpu, r);
> -	/* The cpu is set in default rdtgroup after online. */
> -	cpumask_set_cpu(cpu, &rdtgroup_default.cpu_mask);
>  	clear_closid_rmid(cpu);
> +
> +	ret = resctrl_online_cpu(cpu);
>  	mutex_unlock(&rdtgroup_mutex);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static void clear_childcpus(struct rdtgroup *r, unsigned int cpu)
> @@ -965,7 +966,7 @@ static int __init resctrl_late_init(void)
>  
>  	state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
>  				  "x86/resctrl/cat:online:",
> -				  resctrl_online_cpu, resctrl_offline_cpu);
> +				  resctrl_arch_online_cpu, resctrl_offline_cpu);
>  	if (state < 0)
>  		return state;
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 5330c0bdeffc..7c3de5ea0482 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3725,6 +3725,16 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>  	return 0;
>  }
>  
> +int resctrl_online_cpu(unsigned int cpu)
> +{
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	/* The cpu is set in default rdtgroup after online. */

I know that you just copied this but please use CPU instead of cpu.

Reinette

[PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[James Morse]

When a CPU is taken offline resctrl may need to move the overflow or
limbo handlers to run on a different CPU.

Once the offline callbacks have been split, cqm_setup_limbo_handler()
will be called while the CPU that is going offline is still present
in the cpu_mask.

Pass the CPU to exclude to cqm_setup_limbo_handler() and
mbm_setup_overflow_handler(). These functions can use a variant of
cpumask_any_but() when selecting the CPU. -1 is used to indicate no CPUs
need excluding.

A subsequent patch moves these calls to be before CPUs have been removed,
so this exclude_cpus behaviour is temporary.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v2:
 * Rephrased a comment to avoid a two letter bad-word. (we)
 * Avoid assigning mbm_work_cpu if the domain is going to be free()d
 * Added cpumask_any_housekeeping_but(), I dislike the name

Changes since v3:
 * Marked an explanatory comment as temporary as the subsequent patch is
   no longer adjacent.
---
 arch/x86/kernel/cpu/resctrl/core.c     |  8 +++--
 arch/x86/kernel/cpu/resctrl/internal.h | 37 +++++++++++++++++++++--
 arch/x86/kernel/cpu/resctrl/monitor.c  | 42 +++++++++++++++++++++-----
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  6 ++--
 include/linux/resctrl.h                |  3 ++
 5 files changed, 82 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index e00f3542e60e..187ed127a446 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -582,12 +582,16 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 	if (r == &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl) {
 		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
 			cancel_delayed_work(&d->mbm_over);
-			mbm_setup_overflow_handler(d, 0);
+			/*
+			 * temporary: exclude_cpu=-1 as this CPU has already
+			 * been removed by cpumask_clear_cpu()d
+			 */
+			mbm_setup_overflow_handler(d, 0, RESCTRL_PICK_ANY_CPU);
 		}
 		if (is_llc_occupancy_enabled() && cpu == d->cqm_work_cpu &&
 		    has_busy_rmid(r, d)) {
 			cancel_delayed_work(&d->cqm_limbo);
-			cqm_setup_limbo_handler(d, 0);
+			cqm_setup_limbo_handler(d, 0, RESCTRL_PICK_ANY_CPU);
 		}
 	}
 }
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 021a8956518c..9cba8fc405b9 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -79,6 +79,37 @@ static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
 	return cpu;
 }
 
+/**
+ * cpumask_any_housekeeping_but() - Chose any cpu in @mask, preferring those
+ *			            that aren't marked nohz_full, excluding
+ *				    the provided CPU
+ * @mask:	The mask to pick a CPU from.
+ * @exclude_cpu:The CPU to avoid picking.
+ *
+ * Returns a CPU from @mask, but not @but. If there are housekeeping CPUs that
+ * don't use nohz_full, these are preferred.
+ * Returns >= nr_cpu_ids if no CPUs are available.
+ */
+static inline unsigned int
+cpumask_any_housekeeping_but(const struct cpumask *mask, int exclude_cpu)
+{
+	int cpu, hk_cpu;
+
+	cpu = cpumask_any_but(mask, exclude_cpu);
+	if (tick_nohz_full_cpu(cpu)) {
+		hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
+		if  (hk_cpu == exclude_cpu) {
+			hk_cpu = cpumask_nth_andnot(1, mask,
+						    tick_nohz_full_mask);
+		}
+
+		if (hk_cpu < nr_cpu_ids)
+			cpu = hk_cpu;
+	}
+
+	return cpu;
+}
+
 struct rdt_fs_context {
 	struct kernfs_fs_context	kfc;
 	bool				enable_cdpl2;
@@ -564,11 +595,13 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 		    struct rdt_domain *d, struct rdtgroup *rdtgrp,
 		    int evtid, int first);
 void mbm_setup_overflow_handler(struct rdt_domain *dom,
-				unsigned long delay_ms);
+				unsigned long delay_ms,
+				int exclude_cpu);
 void mbm_handle_overflow(struct work_struct *work);
 void __init intel_rdt_mbm_apply_quirk(void);
 bool is_mba_sc(struct rdt_resource *r);
-void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms);
+void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms,
+			     int exclude_cpu);
 void cqm_handle_limbo(struct work_struct *work);
 bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);
 void __check_limbo(struct rdt_domain *d, bool force_free);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ced933694f60..ae02185f3354 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -485,7 +485,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 		 * setup up the limbo worker.
 		 */
 		if (!has_busy_rmid(r, d))
-			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL);
+			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL, -1);
 		set_bit(idx, d->rmid_busy_llc);
 		entry->busy++;
 	}
@@ -810,15 +810,28 @@ void cqm_handle_limbo(struct work_struct *work)
 	mutex_unlock(&rdtgroup_mutex);
 }
 
-void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms)
+/**
+ * cqm_setup_limbo_handler() - Schedule the limbo handler to run for this
+ *                             domain.
+ * @delay_ms:      How far in the future the handler should run.
+ * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any CPU.
+ */
+void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms,
+			     int exclude_cpu)
 {
 	unsigned long delay = msecs_to_jiffies(delay_ms);
 	int cpu;
 
-	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
-	dom->cqm_work_cpu = cpu;
+	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
+		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
+	else
+		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
+						   exclude_cpu);
 
-	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
+	if (cpu < nr_cpu_ids) {
+		dom->cqm_work_cpu = cpu;
+		schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
+	}
 }
 
 void mbm_handle_overflow(struct work_struct *work)
@@ -864,7 +877,14 @@ void mbm_handle_overflow(struct work_struct *work)
 	mutex_unlock(&rdtgroup_mutex);
 }
 
-void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
+/**
+ * mbm_setup_overflow_handler() - Schedule the overflow handler to run for this
+ *                                domain.
+ * @delay_ms:      How far in the future the handler should run.
+ * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any CPU.
+ */
+void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms,
+				int exclude_cpu)
 {
 	unsigned long delay = msecs_to_jiffies(delay_ms);
 	int cpu;
@@ -875,9 +895,15 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 	 */
 	if (!resctrl_mounted || !resctrl_arch_mon_capable())
 		return;
-	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
+	if (exclude_cpu == -1)
+		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
+	else
+		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
+						   exclude_cpu);
 	dom->mbm_work_cpu = cpu;
-	schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
+
+	if (cpu < nr_cpu_ids)
+		schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
 }
 
 static int dom_data_init(struct rdt_resource *r)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 7c3de5ea0482..3373b11afe01 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2539,7 +2539,8 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (is_mbm_enabled()) {
 		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
 		list_for_each_entry(dom, &r->domains, list)
-			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL);
+			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL,
+						   RESCTRL_PICK_ANY_CPU);
 	}
 
 	goto out;
@@ -3709,7 +3710,8 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
 
 	if (is_mbm_enabled()) {
 		INIT_DELAYED_WORK(&d->mbm_over, mbm_handle_overflow);
-		mbm_setup_overflow_handler(d, MBM_OVERFLOW_INTERVAL);
+		mbm_setup_overflow_handler(d, MBM_OVERFLOW_INTERVAL,
+					   RESCTRL_PICK_ANY_CPU);
 	}
 
 	if (is_llc_occupancy_enabled())
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index ecd41762d61a..089b91133e5e 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -9,6 +9,9 @@
 /* CLOSID value used by the default control group */
 #define RESCTRL_RESERVED_CLOSID		0
 
+/* Indicates no CPU needs to be excluded */
+#define RESCTRL_PICK_ANY_CPU		-1
+
 #ifdef CONFIG_PROC_CPU_RESCTRL
 
 int proc_resctrl_show(struct seq_file *m,
-- 
2.39.2

RE: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[Shaopeng Tan (Fujitsu)]

Hi James,

> When a CPU is taken offline resctrl may need to move the overflow or limbo
> handlers to run on a different CPU.
> 
> Once the offline callbacks have been split, cqm_setup_limbo_handler() will be
> called while the CPU that is going offline is still present in the cpu_mask.
> 
> Pass the CPU to exclude to cqm_setup_limbo_handler() and
> mbm_setup_overflow_handler(). These functions can use a variant of
> cpumask_any_but() when selecting the CPU. -1 is used to indicate no CPUs
> need excluding.
> 
> A subsequent patch moves these calls to be before CPUs have been removed,
> so this exclude_cpus behaviour is temporary.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v2:
>  * Rephrased a comment to avoid a two letter bad-word. (we)
>  * Avoid assigning mbm_work_cpu if the domain is going to be free()d
>  * Added cpumask_any_housekeeping_but(), I dislike the name
> 
> Changes since v3:
>  * Marked an explanatory comment as temporary as the subsequent patch is
>    no longer adjacent.
> ---
>  arch/x86/kernel/cpu/resctrl/core.c     |  8 +++--
>  arch/x86/kernel/cpu/resctrl/internal.h | 37
> +++++++++++++++++++++--  arch/x86/kernel/cpu/resctrl/monitor.c
> | 42 +++++++++++++++++++++-----
> arch/x86/kernel/cpu/resctrl/rdtgroup.c |  6 ++--
>  include/linux/resctrl.h                |  3 ++
>  5 files changed, 82 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c
> b/arch/x86/kernel/cpu/resctrl/core.c
> index e00f3542e60e..187ed127a446 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -582,12 +582,16 @@ static void domain_remove_cpu(int cpu, struct
> rdt_resource *r)
>  	if (r == &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl) {
>  		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
>  			cancel_delayed_work(&d->mbm_over);
> -			mbm_setup_overflow_handler(d, 0);
> +			/*
> +			 * temporary: exclude_cpu=-1 as this CPU has
> already
> +			 * been removed by cpumask_clear_cpu()d
> +			 */
> +			mbm_setup_overflow_handler(d, 0,
> RESCTRL_PICK_ANY_CPU);
>  		}
>  		if (is_llc_occupancy_enabled() && cpu ==
> d->cqm_work_cpu &&
>  		    has_busy_rmid(r, d)) {
>  			cancel_delayed_work(&d->cqm_limbo);
> -			cqm_setup_limbo_handler(d, 0);
> +			cqm_setup_limbo_handler(d, 0,
> RESCTRL_PICK_ANY_CPU);
>  		}
>  	}
>  }
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
> b/arch/x86/kernel/cpu/resctrl/internal.h
> index 021a8956518c..9cba8fc405b9 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -79,6 +79,37 @@ static inline unsigned int
> cpumask_any_housekeeping(const struct cpumask *mask)
>  	return cpu;
>  }
> 
> +/**
> + * cpumask_any_housekeeping_but() - Chose any cpu in @mask, preferring
> those
> + *			            that aren't marked nohz_full, excluding
> + *				    the provided CPU
> + * @mask:	The mask to pick a CPU from.
> + * @exclude_cpu:The CPU to avoid picking.
> + *
> + * Returns a CPU from @mask, but not @but. If there are housekeeping
> +CPUs that
> + * don't use nohz_full, these are preferred.
> + * Returns >= nr_cpu_ids if no CPUs are available.
> + */
> +static inline unsigned int
> +cpumask_any_housekeeping_but(const struct cpumask *mask, int
> +exclude_cpu) {
> +	int cpu, hk_cpu;
> +
> +	cpu = cpumask_any_but(mask, exclude_cpu);
> +	if (tick_nohz_full_cpu(cpu)) {
> +		hk_cpu = cpumask_nth_andnot(0, mask,
> tick_nohz_full_mask);
> +		if  (hk_cpu == exclude_cpu) {
> +			hk_cpu = cpumask_nth_andnot(1, mask,
> +						    tick_nohz_full_mask);
> +		}
> +
> +		if (hk_cpu < nr_cpu_ids)
> +			cpu = hk_cpu;
> +	}
> +
> +	return cpu;
> +}
> +
>  struct rdt_fs_context {
>  	struct kernfs_fs_context	kfc;
>  	bool				enable_cdpl2;
> @@ -564,11 +595,13 @@ void mon_event_read(struct rmid_read *rr, struct
> rdt_resource *r,
>  		    struct rdt_domain *d, struct rdtgroup *rdtgrp,
>  		    int evtid, int first);
>  void mbm_setup_overflow_handler(struct rdt_domain *dom,
> -				unsigned long delay_ms);
> +				unsigned long delay_ms,
> +				int exclude_cpu);
>  void mbm_handle_overflow(struct work_struct *work);  void __init
> intel_rdt_mbm_apply_quirk(void);  bool is_mba_sc(struct rdt_resource *r);
> -void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms);
> +void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms,
> +			     int exclude_cpu);
>  void cqm_handle_limbo(struct work_struct *work);  bool
> has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);  void
> __check_limbo(struct rdt_domain *d, bool force_free); diff --git
> a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index ced933694f60..ae02185f3354 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -485,7 +485,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  		 * setup up the limbo worker.
>  		 */
>  		if (!has_busy_rmid(r, d))
> -			cqm_setup_limbo_handler(d,
> CQM_LIMBOCHECK_INTERVAL);
> +			cqm_setup_limbo_handler(d,
> CQM_LIMBOCHECK_INTERVAL, -1);
>  		set_bit(idx, d->rmid_busy_llc);
>  		entry->busy++;
>  	}
> @@ -810,15 +810,28 @@ void cqm_handle_limbo(struct work_struct *work)
>  	mutex_unlock(&rdtgroup_mutex);
>  }
> 
> -void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms)
> +/**
> + * cqm_setup_limbo_handler() - Schedule the limbo handler to run for this
> + *                             domain.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any
> CPU.
> + */
> +void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long
> delay_ms,
> +			     int exclude_cpu)
>  {
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
> 
> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> -	dom->cqm_work_cpu = cpu;
> +	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> +	else
> +		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
> +						   exclude_cpu);
> 
> -	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> +	if (cpu < nr_cpu_ids) {
> +		dom->cqm_work_cpu = cpu;
> +		schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> +	}
>  }
> 
>  void mbm_handle_overflow(struct work_struct *work) @@ -864,7 +877,14
> @@ void mbm_handle_overflow(struct work_struct *work)
>  	mutex_unlock(&rdtgroup_mutex);
>  }
> 
> -void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long
> delay_ms)
> +/**
> + * mbm_setup_overflow_handler() - Schedule the overflow handler to run for
> this
> + *                                domain.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any
> CPU.
> + */
> +void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long
> delay_ms,
> +				int exclude_cpu)
>  {
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
> @@ -875,9 +895,15 @@ void mbm_setup_overflow_handler(struct rdt_domain
> *dom, unsigned long delay_ms)
>  	 */
>  	if (!resctrl_mounted || !resctrl_arch_mon_capable())
>  		return;
> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> +	if (exclude_cpu == -1)
> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);

Should RESCTRL_PICK_ANY_CPU be used instead of -1?

Best regards,
Shaopeng TAN

Re: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[James Morse]

Hi Shaopeng Tan,

On 09/06/2023 12:10, Shaopeng Tan (Fujitsu) wrote:
>> When a CPU is taken offline resctrl may need to move the overflow or limbo
>> handlers to run on a different CPU.
>>
>> Once the offline callbacks have been split, cqm_setup_limbo_handler() will be
>> called while the CPU that is going offline is still present in the cpu_mask.
>>
>> Pass the CPU to exclude to cqm_setup_limbo_handler() and
>> mbm_setup_overflow_handler(). These functions can use a variant of
>> cpumask_any_but() when selecting the CPU. -1 is used to indicate no CPUs
>> need excluding.
>>
>> A subsequent patch moves these calls to be before CPUs have been removed,
>> so this exclude_cpus behaviour is temporary.

>> diff --git
>> a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index ced933694f60..ae02185f3354 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -875,9 +895,15 @@ void mbm_setup_overflow_handler(struct rdt_domain
>> *dom, unsigned long delay_ms)
>>  	 */
>>  	if (!resctrl_mounted || !resctrl_arch_mon_capable())
>>  		return;
>> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
>> +	if (exclude_cpu == -1)
>> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> 
> Should RESCTRL_PICK_ANY_CPU be used instead of -1?

Yup, that would be more readable. I did this for cqm_setup_limbo_handler(), but for some
reason missed this one.


Thanks,

James

Re: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[Reinette Chatre]

Hi James,

On 5/25/2023 11:02 AM, James Morse wrote:

...

> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 021a8956518c..9cba8fc405b9 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -79,6 +79,37 @@ static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
>  	return cpu;
>  }
>  
> +/**
> + * cpumask_any_housekeeping_but() - Chose any cpu in @mask, preferring those
> + *			            that aren't marked nohz_full, excluding
> + *				    the provided CPU
> + * @mask:	The mask to pick a CPU from.
> + * @exclude_cpu:The CPU to avoid picking.
> + *
> + * Returns a CPU from @mask, but not @but. If there are housekeeping CPUs that

"but not @exclude_cpu"

> + * don't use nohz_full, these are preferred.
> + * Returns >= nr_cpu_ids if no CPUs are available.
> + */
> +static inline unsigned int
> +cpumask_any_housekeeping_but(const struct cpumask *mask, int exclude_cpu)
> +{
> +	int cpu, hk_cpu;

Should these be unsigned int?

> +
> +	cpu = cpumask_any_but(mask, exclude_cpu);
> +	if (tick_nohz_full_cpu(cpu)) {
> +		hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
> +		if  (hk_cpu == exclude_cpu) {
> +			hk_cpu = cpumask_nth_andnot(1, mask,
> +						    tick_nohz_full_mask);
> +		}
> +

These braces are not necessary. If they are added to help readability then
perhaps the indentation can be reduced by using an earlier:

	if (!tick_nohz_full_cpu(cpu))
		return cpu;


> +		if (hk_cpu < nr_cpu_ids)
> +			cpu = hk_cpu;
> +	}
> +
> +	return cpu;
> +}
> +
>  struct rdt_fs_context {
>  	struct kernfs_fs_context	kfc;
>  	bool				enable_cdpl2;
> @@ -564,11 +595,13 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  		    struct rdt_domain *d, struct rdtgroup *rdtgrp,
>  		    int evtid, int first);
>  void mbm_setup_overflow_handler(struct rdt_domain *dom,
> -				unsigned long delay_ms);
> +				unsigned long delay_ms,
> +				int exclude_cpu);
>  void mbm_handle_overflow(struct work_struct *work);
>  void __init intel_rdt_mbm_apply_quirk(void);
>  bool is_mba_sc(struct rdt_resource *r);
> -void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms);
> +void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms,
> +			     int exclude_cpu);
>  void cqm_handle_limbo(struct work_struct *work);
>  bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);
>  void __check_limbo(struct rdt_domain *d, bool force_free);
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index ced933694f60..ae02185f3354 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -485,7 +485,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  		 * setup up the limbo worker.
>  		 */
>  		if (!has_busy_rmid(r, d))
> -			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL);
> +			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL, -1);

Should this -1 be RESCTRL_PICK_ANY_CPU?

>  		set_bit(idx, d->rmid_busy_llc);
>  		entry->busy++;
>  	}
> @@ -810,15 +810,28 @@ void cqm_handle_limbo(struct work_struct *work)
>  	mutex_unlock(&rdtgroup_mutex);
>  }
>  
> -void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms)
> +/**
> + * cqm_setup_limbo_handler() - Schedule the limbo handler to run for this
> + *                             domain.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any CPU.

Should -1 be RESCTRL_PICK_ANY_CPU? 

> + */
> +void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms,
> +			     int exclude_cpu)
>  {
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
>  
> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> -	dom->cqm_work_cpu = cpu;
> +	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> +	else
> +		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
> +						   exclude_cpu);
>  
> -	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> +	if (cpu < nr_cpu_ids) {
> +		dom->cqm_work_cpu = cpu;

Should cqm_work_cpu not perhaps be set to nr_cpu_ids on failure? If it keeps
pointing to CPU that ran worker previously there may be unexpected behavior. 

Note the different behavior between cqm_setup_limbo_handler() and
mbm_setup_overflow_handler() in this regard.

> +		schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
> +	}
>  }
>  
>  void mbm_handle_overflow(struct work_struct *work)
> @@ -864,7 +877,14 @@ void mbm_handle_overflow(struct work_struct *work)
>  	mutex_unlock(&rdtgroup_mutex);
>  }
>  
> -void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
> +/**
> + * mbm_setup_overflow_handler() - Schedule the overflow handler to run for this
> + *                                domain.
> + * @delay_ms:      How far in the future the handler should run.
> + * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any CPU.

RESCTRL_PICK_ANY_CPU?

> + */
> +void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms,
> +				int exclude_cpu)
>  {
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
> @@ -875,9 +895,15 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
>  	 */
>  	if (!resctrl_mounted || !resctrl_arch_mon_capable())
>  		return;
> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> +	if (exclude_cpu == -1)

same

> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> +	else
> +		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
> +						   exclude_cpu);
>  	dom->mbm_work_cpu = cpu;
> -	schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
> +
> +	if (cpu < nr_cpu_ids)
> +		schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
>  }
>  

...

> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index ecd41762d61a..089b91133e5e 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -9,6 +9,9 @@
>  /* CLOSID value used by the default control group */
>  #define RESCTRL_RESERVED_CLOSID		0
>  
> +/* Indicates no CPU needs to be excluded */

This comment seems to just be a rewrite of the macro name.

> +#define RESCTRL_PICK_ANY_CPU		-1
> +
>  #ifdef CONFIG_PROC_CPU_RESCTRL
>  
>  int proc_resctrl_show(struct seq_file *m,

Reinette

Re: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[James Morse]

Hi Reinette,

On 15/06/2023 23:25, Reinette Chatre wrote:
> On 5/25/2023 11:02 AM, James Morse wrote:
>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
>> index 021a8956518c..9cba8fc405b9 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -79,6 +79,37 @@ static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
>>  	return cpu;
>>  }
>>  
>> +/**
>> + * cpumask_any_housekeeping_but() - Chose any cpu in @mask, preferring those
>> + *			            that aren't marked nohz_full, excluding
>> + *				    the provided CPU
>> + * @mask:	The mask to pick a CPU from.
>> + * @exclude_cpu:The CPU to avoid picking.
>> + *
>> + * Returns a CPU from @mask, but not @but. If there are housekeeping CPUs that
> 
> "but not @exclude_cpu"
> 
>> + * don't use nohz_full, these are preferred.
>> + * Returns >= nr_cpu_ids if no CPUs are available.
>> + */
>> +static inline unsigned int
>> +cpumask_any_housekeeping_but(const struct cpumask *mask, int exclude_cpu)
>> +{
>> +	int cpu, hk_cpu;
> 
> Should these be unsigned int?

Yup, fixed.


>> +
>> +	cpu = cpumask_any_but(mask, exclude_cpu);
>> +	if (tick_nohz_full_cpu(cpu)) {
>> +		hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
>> +		if  (hk_cpu == exclude_cpu) {
>> +			hk_cpu = cpumask_nth_andnot(1, mask,
>> +						    tick_nohz_full_mask);
>> +		}
>> +
> 
> These braces are not necessary.

My C parser is pretty dumb, and is easily confused by things like that....


> If they are added to help readability then
> perhaps the indentation can be reduced by using an earlier:
> 
> 	if (!tick_nohz_full_cpu(cpu))
> 		return cpu;

Even better!


>> +		if (hk_cpu < nr_cpu_ids)
>> +			cpu = hk_cpu;
>> +	}
>> +
>> +	return cpu;
>> +}
>> +
>>  struct rdt_fs_context {
>>  	struct kernfs_fs_context	kfc;
>>  	bool				enable_cdpl2;

>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index ced933694f60..ae02185f3354 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -485,7 +485,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>>  		 * setup up the limbo worker.
>>  		 */
>>  		if (!has_busy_rmid(r, d))
>> -			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL);
>> +			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL, -1);
> 
> Should this -1 be RESCTRL_PICK_ANY_CPU?
> 
>>  		set_bit(idx, d->rmid_busy_llc);
>>  		entry->busy++;
>>  	}
>> @@ -810,15 +810,28 @@ void cqm_handle_limbo(struct work_struct *work)
>>  	mutex_unlock(&rdtgroup_mutex);
>>  }
>>  
>> -void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms)
>> +/**
>> + * cqm_setup_limbo_handler() - Schedule the limbo handler to run for this
>> + *                             domain.
>> + * @delay_ms:      How far in the future the handler should run.
>> + * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any CPU.
> 
> Should -1 be RESCTRL_PICK_ANY_CPU? 
> 
>> + */
>> +void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms,
>> +			     int exclude_cpu)
>>  {
>>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>>  	int cpu;
>>  
>> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
>> -	dom->cqm_work_cpu = cpu;
>> +	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
>> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
>> +	else
>> +		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
>> +						   exclude_cpu);
>>  
>> -	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
>> +	if (cpu < nr_cpu_ids) {
>> +		dom->cqm_work_cpu = cpu;
> 
> Should cqm_work_cpu not perhaps be set to nr_cpu_ids on failure? If it keeps
> pointing to CPU that ran worker previously there may be unexpected behavior. 
> 
> Note the different behavior between cqm_setup_limbo_handler() and
> mbm_setup_overflow_handler() in this regard.

Sure,


>> +		schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
>> +	}
>>  }
>>  
>>  void mbm_handle_overflow(struct work_struct *work)

>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>> index ecd41762d61a..089b91133e5e 100644
>> --- a/include/linux/resctrl.h
>> +++ b/include/linux/resctrl.h
>> @@ -9,6 +9,9 @@
>>  /* CLOSID value used by the default control group */
>>  #define RESCTRL_RESERVED_CLOSID		0
>>  
>> +/* Indicates no CPU needs to be excluded */
> 
> This comment seems to just be a rewrite of the macro name.

I'm more than happy to remove it!



Thanks,

James

[PATCH v4 22/24] x86/resctrl: Add cpu offline callback for resctrl work

[James Morse]

The resctrl architecture specific code may need to free a domain when
a CPU goes offline, it also needs to reset the CPUs PQR_ASSOC register.
Amongst other things, the resctrl filesystem code needs to clear this
CPU from the cpu_mask of any control and monitor groups.

Currently this is all done in core.c and called from
resctrl_offline_cpu(), making the split between architecture and
filesystem code unclear.

Move the filesystem work to remove the CPU from the control and monitor
groups into a filesystem helper called resctrl_offline_cpu(), and rename
the one in core.c resctrl_arch_offline_cpu().

The rdtgroup_mutex is unlocked and locked again in the call in
preparation for changing the locking rules for the architecture
code.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/core.c     | 25 +++++--------------------
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 24 ++++++++++++++++++++++++
 include/linux/resctrl.h                |  1 +
 3 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 187ed127a446..9128a9710537 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -623,31 +623,15 @@ static int resctrl_arch_online_cpu(unsigned int cpu)
 	return ret;
 }
 
-static void clear_childcpus(struct rdtgroup *r, unsigned int cpu)
+static int resctrl_arch_offline_cpu(unsigned int cpu)
 {
-	struct rdtgroup *cr;
-
-	list_for_each_entry(cr, &r->mon.crdtgrp_list, mon.crdtgrp_list) {
-		if (cpumask_test_and_clear_cpu(cpu, &cr->cpu_mask)) {
-			break;
-		}
-	}
-}
-
-static int resctrl_offline_cpu(unsigned int cpu)
-{
-	struct rdtgroup *rdtgrp;
 	struct rdt_resource *r;
 
 	mutex_lock(&rdtgroup_mutex);
+	resctrl_offline_cpu(cpu);
+
 	for_each_capable_rdt_resource(r)
 		domain_remove_cpu(cpu, r);
-	list_for_each_entry(rdtgrp, &rdt_all_groups, rdtgroup_list) {
-		if (cpumask_test_and_clear_cpu(cpu, &rdtgrp->cpu_mask)) {
-			clear_childcpus(rdtgrp, cpu);
-			break;
-		}
-	}
 	clear_closid_rmid(cpu);
 	mutex_unlock(&rdtgroup_mutex);
 
@@ -970,7 +954,8 @@ static int __init resctrl_late_init(void)
 
 	state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				  "x86/resctrl/cat:online:",
-				  resctrl_arch_online_cpu, resctrl_offline_cpu);
+				  resctrl_arch_online_cpu,
+				  resctrl_arch_offline_cpu);
 	if (state < 0)
 		return state;
 
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 3373b11afe01..08b426f52f6d 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3737,6 +3737,30 @@ int resctrl_online_cpu(unsigned int cpu)
 	return 0;
 }
 
+static void clear_childcpus(struct rdtgroup *r, unsigned int cpu)
+{
+	struct rdtgroup *cr;
+
+	list_for_each_entry(cr, &r->mon.crdtgrp_list, mon.crdtgrp_list) {
+		if (cpumask_test_and_clear_cpu(cpu, &cr->cpu_mask))
+			break;
+	}
+}
+
+void resctrl_offline_cpu(unsigned int cpu)
+{
+	struct rdtgroup *rdtgrp;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	list_for_each_entry(rdtgrp, &rdt_all_groups, rdtgroup_list) {
+		if (cpumask_test_and_clear_cpu(cpu, &rdtgrp->cpu_mask)) {
+			clear_childcpus(rdtgrp, cpu);
+			break;
+		}
+	}
+}
+
 /*
  * rdtgroup_init - rdtgroup initialization
  *
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 089b91133e5e..c4be3453b3ff 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -226,6 +226,7 @@ u32 resctrl_arch_get_config(struct rdt_resource *r, struct rdt_domain *d,
 int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d);
 void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
 int resctrl_online_cpu(unsigned int cpu);
+void resctrl_offline_cpu(unsigned int cpu);
 
 /**
  * resctrl_arch_rmid_read() - Read the eventid counter corresponding to rmid
-- 
2.39.2

[PATCH v4 23/24] x86/resctrl: Move domain helper migration into resctrl_offline_cpu()

[James Morse]

When a CPU is taken offline the resctrl filesystem code needs to check
if it was the CPU nominated to perform the periodic overflow and limbo
work. If so, another CPU needs to be chosen to do this work.

This is currently done in core.c, mixed in with the code that removes
the CPU from the domain's mask, and potentially free()s the domain.

Move the migration of the overflow and limbo helpers into the filesystem
code, into resctrl_offline_cpu(). As resctrl_offline_cpu() runs before
the architecture code has removed the CPU from the domain mask, the
callers need to be told which CPU is being removed, to avoid picking
it as the new CPU. This uses the exclude_cpu feature previously
added.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/core.c     | 16 ----------------
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 15 +++++++++++++++
 2 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 9128a9710537..edc0dd123317 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -578,22 +578,6 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 
 		return;
 	}
-
-	if (r == &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl) {
-		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
-			cancel_delayed_work(&d->mbm_over);
-			/*
-			 * temporary: exclude_cpu=-1 as this CPU has already
-			 * been removed by cpumask_clear_cpu()d
-			 */
-			mbm_setup_overflow_handler(d, 0, RESCTRL_PICK_ANY_CPU);
-		}
-		if (is_llc_occupancy_enabled() && cpu == d->cqm_work_cpu &&
-		    has_busy_rmid(r, d)) {
-			cancel_delayed_work(&d->cqm_limbo);
-			cqm_setup_limbo_handler(d, 0, RESCTRL_PICK_ANY_CPU);
-		}
-	}
 }
 
 static void clear_closid_rmid(int cpu)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 08b426f52f6d..3a8e2c98b611 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3749,7 +3749,9 @@ static void clear_childcpus(struct rdtgroup *r, unsigned int cpu)
 
 void resctrl_offline_cpu(unsigned int cpu)
 {
+	struct rdt_domain *d;
 	struct rdtgroup *rdtgrp;
+	struct rdt_resource *l3 = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
 
 	lockdep_assert_held(&rdtgroup_mutex);
 
@@ -3759,6 +3761,19 @@ void resctrl_offline_cpu(unsigned int cpu)
 			break;
 		}
 	}
+
+	d = get_domain_from_cpu(cpu, l3);
+	if (d) {
+		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
+			cancel_delayed_work(&d->mbm_over);
+			mbm_setup_overflow_handler(d, 0, cpu);
+		}
+		if (is_llc_occupancy_enabled() && cpu == d->cqm_work_cpu &&
+		    has_busy_rmid(l3, d)) {
+			cancel_delayed_work(&d->cqm_limbo);
+			cqm_setup_limbo_handler(d, 0, cpu);
+		}
+	}
 }
 
 /*
-- 
2.39.2

[PATCH v4 24/24] x86/resctrl: Separate arch and fs resctrl locks

[James Morse]

resctrl has one mutex that is taken by the architecture specific code,
and the filesystem parts. The two interact via cpuhp, where the
architecture code updates the domain list. Filesystem handlers that
walk the domains list should not run concurrently with the cpuhp
callback modifying the list.

Exposing a lock from the filesystem code means the interface is not
cleanly defined, and creates the possibility of cross-architecture
lock ordering headaches. The interaction only exists so that certain
filesystem paths are serialised against cpu hotplug. The cpu hotplug
code already has a mechanism to do this using cpus_read_lock().

MPAM's monitors have an overflow interrupt, so it needs to be possible
to walk the domains list in irq context. RCU is ideal for this,
but some paths need to be able to sleep to allocate memory.

Because resctrl_{on,off}line_cpu() take the rdtgroup_mutex as part
of a cpuhp callback, cpus_read_lock() must always be taken first.
rdtgroup_schemata_write() already does this.

Most of the filesystem code's domain list walkers are currently
protected by the rdtgroup_mutex taken in rdtgroup_kn_lock_live().
The exceptions are rdt_bit_usage_show() and the mon_config helpers
which take the lock directly.

Make the domain list protected by RCU. An architecture-specific
lock prevents concurrent writers. rdt_bit_usage_show() can
walk the domain list under rcu_read_lock(). The mon_config helpers
send multiple IPIs, take the cpus_read_lock() in these cases.

The other filesystem list walkers need to be able to sleep.
Add cpus_read_lock() to rdtgroup_kn_lock_live() so that the
cpuhp callbacks can't be invoked when file system operations are
occurring.

Add lockdep_assert_cpus_held() in the cases where the
rdtgroup_kn_lock_live() call isn't obvious.

Resctrl's domain online/offline calls now need to take the
rdtgroup_mutex themselves.

Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v2:
 * Reworded a comment,
 * Added a lockdep assertion
 * Moved clear_closid_rmid() outside the locked region of cpu
   online/offline

Changes since v3:
 * Added a header include
---
 arch/x86/kernel/cpu/resctrl/core.c        | 38 +++++++++-----
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 16 ++++--
 arch/x86/kernel/cpu/resctrl/monitor.c     |  4 ++
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  3 ++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 63 ++++++++++++++++++++---
 include/linux/resctrl.h                   |  2 +-
 6 files changed, 100 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index edc0dd123317..f106c68a9be8 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -25,8 +25,15 @@
 #include <asm/resctrl.h>
 #include "internal.h"
 
-/* Mutex to protect rdtgroup access. */
-DEFINE_MUTEX(rdtgroup_mutex);
+/*
+ * rdt_domain structures are kfree()d when their last CPU goes offline,
+ * and allocated when the first CPU in a new domain comes online.
+ * The rdt_resource's domain list is updated when this happens. Readers of
+ * the domain list must either take cpus_read_lock(), or rely on an RCU
+ * read-side critical section, to avoid observing concurrent modification.
+ * All writers take this mutex:
+ */
+static DEFINE_MUTEX(domain_list_lock);
 
 /*
  * The cached resctrl_pqr_state is strictly per CPU and can never be
@@ -508,6 +515,8 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
 	struct rdt_domain *d;
 	int err;
 
+	lockdep_assert_held(&domain_list_lock);
+
 	d = rdt_find_domain(r, id, &add_pos);
 	if (IS_ERR(d)) {
 		pr_warn("Couldn't find cache id for CPU %d\n", cpu);
@@ -541,11 +550,12 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
 		return;
 	}
 
-	list_add_tail(&d->list, add_pos);
+	list_add_tail_rcu(&d->list, add_pos);
 
 	err = resctrl_online_domain(r, d);
 	if (err) {
-		list_del(&d->list);
+		list_del_rcu(&d->list);
+		synchronize_rcu();
 		domain_free(hw_dom);
 	}
 }
@@ -556,6 +566,8 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 	struct rdt_hw_domain *hw_dom;
 	struct rdt_domain *d;
 
+	lockdep_assert_held(&domain_list_lock);
+
 	d = rdt_find_domain(r, id, NULL);
 	if (IS_ERR_OR_NULL(d)) {
 		pr_warn("Couldn't find cache id for CPU %d\n", cpu);
@@ -566,7 +578,8 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 	cpumask_clear_cpu(cpu, &d->cpu_mask);
 	if (cpumask_empty(&d->cpu_mask)) {
 		resctrl_offline_domain(r, d);
-		list_del(&d->list);
+		list_del_rcu(&d->list);
+		synchronize_rcu();
 
 		/*
 		 * rdt_domain "d" is going to be freed below, so clear
@@ -594,30 +607,29 @@ static void clear_closid_rmid(int cpu)
 static int resctrl_arch_online_cpu(unsigned int cpu)
 {
 	struct rdt_resource *r;
-	int ret;
 
-	mutex_lock(&rdtgroup_mutex);
+	mutex_lock(&domain_list_lock);
 	for_each_capable_rdt_resource(r)
 		domain_add_cpu(cpu, r);
+	mutex_unlock(&domain_list_lock);
+
 	clear_closid_rmid(cpu);
 
-	ret = resctrl_online_cpu(cpu);
-	mutex_unlock(&rdtgroup_mutex);
-
-	return ret;
+	return resctrl_online_cpu(cpu);
 }
 
 static int resctrl_arch_offline_cpu(unsigned int cpu)
 {
 	struct rdt_resource *r;
 
-	mutex_lock(&rdtgroup_mutex);
 	resctrl_offline_cpu(cpu);
 
+	mutex_lock(&domain_list_lock);
 	for_each_capable_rdt_resource(r)
 		domain_remove_cpu(cpu, r);
+	mutex_unlock(&domain_list_lock);
+
 	clear_closid_rmid(cpu);
-	mutex_unlock(&rdtgroup_mutex);
 
 	return 0;
 }
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 280d66fae21c..d8d7c127403b 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -209,6 +209,9 @@ static int parse_line(char *line, struct resctrl_schema *s,
 	struct rdt_domain *d;
 	unsigned long dom_id;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP &&
 	    (r->rid == RDT_RESOURCE_MBA || r->rid == RDT_RESOURCE_SMBA)) {
 		rdt_last_cmd_puts("Cannot pseudo-lock MBA resource\n");
@@ -313,6 +316,9 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
 	struct rdt_domain *d;
 	u32 idx;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
 		return -ENOMEM;
 
@@ -378,11 +384,9 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 		return -EINVAL;
 	buf[nbytes - 1] = '\0';
 
-	cpus_read_lock();
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
 	if (!rdtgrp) {
 		rdtgroup_kn_unlock(of->kn);
-		cpus_read_unlock();
 		return -ENOENT;
 	}
 	rdt_last_cmd_clear();
@@ -444,7 +448,6 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 out:
 	rdt_staged_configs_clear();
 	rdtgroup_kn_unlock(of->kn);
-	cpus_read_unlock();
 	return ret ?: nbytes;
 }
 
@@ -464,6 +467,9 @@ static void show_doms(struct seq_file *s, struct resctrl_schema *schema, int clo
 	bool sep = false;
 	u32 ctrl_val;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	seq_printf(s, "%*s:", max_name_width, schema->name);
 	list_for_each_entry(dom, &r->domains, list) {
 		if (sep)
@@ -534,8 +540,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 {
 	int cpu;
 
-	/* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */
-	lockdep_assert_held(&rdtgroup_mutex);
+	/* When picking a cpu from cpu_mask, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
 
 	/*
 	 * setup the parameters to pass to mon_event_count() to read the data.
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ae02185f3354..41b4cd2c7d64 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -15,6 +15,7 @@
  * Software Developer Manual June 2016, volume 3, section 17.17.
  */
 
+#include <linux/cpu.h>
 #include <linux/module.h>
 #include <linux/sizes.h>
 #include <linux/slab.h>
@@ -476,6 +477,9 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 
 	lockdep_assert_held(&rdtgroup_mutex);
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
 
 	entry->busy = 0;
diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index 460421051abf..fc3ed917d173 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -830,6 +830,9 @@ bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_domain *d)
 	struct rdt_domain *d_i;
 	bool ret = false;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	if (!zalloc_cpumask_var(&cpu_with_psl, GFP_KERNEL))
 		return true;
 
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 3a8e2c98b611..9002ac728001 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -35,6 +35,10 @@
 DEFINE_STATIC_KEY_FALSE(rdt_enable_key);
 DEFINE_STATIC_KEY_FALSE(rdt_mon_enable_key);
 DEFINE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
+
+/* Mutex to protect rdtgroup access. */
+DEFINE_MUTEX(rdtgroup_mutex);
+
 static struct kernfs_root *rdt_root;
 struct rdtgroup rdtgroup_default;
 LIST_HEAD(rdt_all_groups);
@@ -950,7 +954,8 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
 
 	mutex_lock(&rdtgroup_mutex);
 	hw_shareable = r->cache.shareable_bits;
-	list_for_each_entry(dom, &r->domains, list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(dom, &r->domains, list) {
 		if (sep)
 			seq_putc(seq, ';');
 		sw_shareable = 0;
@@ -1006,8 +1011,10 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
 		}
 		sep = true;
 	}
+	rcu_read_unlock();
 	seq_putc(seq, '\n');
 	mutex_unlock(&rdtgroup_mutex);
+
 	return 0;
 }
 
@@ -1250,6 +1257,9 @@ static bool rdtgroup_mode_test_exclusive(struct rdtgroup *rdtgrp)
 	struct rdt_domain *d;
 	u32 ctrl;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	list_for_each_entry(s, &resctrl_schema_all, list) {
 		r = s->res;
 		if (r->rid == RDT_RESOURCE_MBA || r->rid == RDT_RESOURCE_SMBA)
@@ -1516,6 +1526,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
 	struct rdt_domain *dom;
 	bool sep = false;
 
+	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 
 	list_for_each_entry(dom, &r->domains, list) {
@@ -1532,6 +1543,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
 	seq_puts(s, "\n");
 
 	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
 
 	return 0;
 }
@@ -1623,6 +1635,9 @@ static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
 	struct rdt_domain *d;
 	int ret = 0;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 next:
 	if (!tok || tok[0] == '\0')
 		return 0;
@@ -1664,6 +1679,7 @@ static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of,
 	if (nbytes == 0 || buf[nbytes - 1] != '\n')
 		return -EINVAL;
 
+	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 
 	rdt_last_cmd_clear();
@@ -1673,6 +1689,7 @@ static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of,
 	ret = mon_config_write(r, buf, QOS_L3_MBM_TOTAL_EVENT_ID);
 
 	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
 
 	return ret ?: nbytes;
 }
@@ -1688,6 +1705,7 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
 	if (nbytes == 0 || buf[nbytes - 1] != '\n')
 		return -EINVAL;
 
+	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 
 	rdt_last_cmd_clear();
@@ -1697,6 +1715,7 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
 	ret = mon_config_write(r, buf, QOS_L3_MBM_LOCAL_EVENT_ID);
 
 	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
 
 	return ret ?: nbytes;
 }
@@ -2149,6 +2168,9 @@ static int set_cache_qos_cfg(int level, bool enable)
 	struct rdt_domain *d;
 	int cpu;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	if (level == RDT_RESOURCE_L3)
 		update = l3_qos_cfg_update;
 	else if (level == RDT_RESOURCE_L2)
@@ -2337,6 +2359,7 @@ struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn)
 	atomic_inc(&rdtgrp->waitcount);
 	kernfs_break_active_protection(kn);
 
+	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 
 	/* Was this group deleted while we waited? */
@@ -2354,6 +2377,7 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
 		return;
 
 	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
 
 	if (atomic_dec_and_test(&rdtgrp->waitcount) &&
 	    (rdtgrp->flags & RDT_DELETED)) {
@@ -2651,6 +2675,9 @@ static int reset_all_ctrls(struct rdt_resource *r)
 	struct rdt_domain *d;
 	int i;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
 		return -ENOMEM;
 
@@ -2935,6 +2962,9 @@ static int mkdir_mondata_subdir_alldom(struct kernfs_node *parent_kn,
 	struct rdt_domain *dom;
 	int ret;
 
+	/* Walking r->domains, ensure it can't race with cpuhp */
+	lockdep_assert_cpus_held();
+
 	list_for_each_entry(dom, &r->domains, list) {
 		ret = mkdir_mondata_subdir(parent_kn, dom, r, prgrp);
 		if (ret)
@@ -3625,7 +3655,8 @@ static void domain_destroy_mon_state(struct rdt_domain *d)
 	kfree(d->mbm_local);
 }
 
-void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
+static void _resctrl_offline_domain(struct rdt_resource *r,
+				    struct rdt_domain *d)
 {
 	lockdep_assert_held(&rdtgroup_mutex);
 
@@ -3660,6 +3691,13 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
 	domain_destroy_mon_state(d);
 }
 
+void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
+{
+	mutex_lock(&rdtgroup_mutex);
+	_resctrl_offline_domain(r, d);
+	mutex_unlock(&rdtgroup_mutex);
+}
+
 static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 {
 	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
@@ -3691,7 +3729,7 @@ static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 	return 0;
 }
 
-int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
+static int _resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
 {
 	int err;
 
@@ -3727,12 +3765,23 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
 	return 0;
 }
 
+int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
+{
+	int err;
+
+	mutex_lock(&rdtgroup_mutex);
+	err = _resctrl_online_domain(r, d);
+	mutex_unlock(&rdtgroup_mutex);
+
+	return err;
+}
+
 int resctrl_online_cpu(unsigned int cpu)
 {
-	lockdep_assert_held(&rdtgroup_mutex);
-
+	mutex_lock(&rdtgroup_mutex);
 	/* The cpu is set in default rdtgroup after online. */
 	cpumask_set_cpu(cpu, &rdtgroup_default.cpu_mask);
+	mutex_unlock(&rdtgroup_mutex);
 
 	return 0;
 }
@@ -3753,8 +3802,7 @@ void resctrl_offline_cpu(unsigned int cpu)
 	struct rdtgroup *rdtgrp;
 	struct rdt_resource *l3 = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
 
-	lockdep_assert_held(&rdtgroup_mutex);
-
+	mutex_lock(&rdtgroup_mutex);
 	list_for_each_entry(rdtgrp, &rdt_all_groups, rdtgroup_list) {
 		if (cpumask_test_and_clear_cpu(cpu, &rdtgrp->cpu_mask)) {
 			clear_childcpus(rdtgrp, cpu);
@@ -3774,6 +3822,7 @@ void resctrl_offline_cpu(unsigned int cpu)
 			cqm_setup_limbo_handler(d, 0, cpu);
 		}
 	}
+	mutex_unlock(&rdtgroup_mutex);
 }
 
 /*
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index c4be3453b3ff..fe94ef3369fa 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -159,7 +159,7 @@ struct resctrl_schema;
  * @cache_level:	Which cache level defines scope of this resource
  * @cache:		Cache allocation related data
  * @membw:		If the component has bandwidth controls, their properties.
- * @domains:		All domains for this resource
+ * @domains:		RCU list of all domains for this resource
  * @name:		Name to use in "schemata" file.
  * @data_width:		Character width of data when displaying
  * @default_ctrl:	Specifies default cache cbm or memory B/W percent.
-- 
2.39.2

Re: [PATCH v4 24/24] x86/resctrl: Separate arch and fs resctrl locks

[Peter Newman]

Hi James,

On Thu, May 25, 2023 at 8:03 PM James Morse <james.morse@arm.com> wrote:
>
> resctrl has one mutex that is taken by the architecture specific code,
> and the filesystem parts. The two interact via cpuhp, where the
> architecture code updates the domain list. Filesystem handlers that
> walk the domains list should not run concurrently with the cpuhp
> callback modifying the list.
>
> Exposing a lock from the filesystem code means the interface is not
> cleanly defined, and creates the possibility of cross-architecture
> lock ordering headaches. The interaction only exists so that certain
> filesystem paths are serialised against cpu hotplug. The cpu hotplug
> code already has a mechanism to do this using cpus_read_lock().
>
> MPAM's monitors have an overflow interrupt, so it needs to be possible
> to walk the domains list in irq context. RCU is ideal for this,
> but some paths need to be able to sleep to allocate memory.

I noticed there's also a call to get_domain_from_cpu() in
rdt_ctrl_update(), which is invoked by IPI when updating a schemata
file, but at least it's a blocking IPI and the caller holds the
rdtgroup_mutex, so the handler is serialized with CPU hotplug.

Taking a step back, I'm concerned about the scalability of searching
these linked-lists of domains in atomic contexts. We already have
machines where the list is 32 entries deep in L3, and much larger in
L2 CAT.

Will the overflow interrupt target a CPU in the correct domain? The
existing domain list search in rdt_ctrl_update() is for the current
CPU's domain, so an alternative there would be to store each CPU's
interrupt-relevant domain pointers in percpu data for quick lookup.

Also, how quickly does the overflow condition need to be serviced? On
Intel, overflow handling deadlines aren't even tight enough to warrant
an interrupt handler.

Thanks!
-Peter





>
> Because resctrl_{on,off}line_cpu() take the rdtgroup_mutex as part
> of a cpuhp callback, cpus_read_lock() must always be taken first.
> rdtgroup_schemata_write() already does this.
>
> Most of the filesystem code's domain list walkers are currently
> protected by the rdtgroup_mutex taken in rdtgroup_kn_lock_live().
> The exceptions are rdt_bit_usage_show() and the mon_config helpers
> which take the lock directly.
>
> Make the domain list protected by RCU. An architecture-specific
> lock prevents concurrent writers. rdt_bit_usage_show() can
> walk the domain list under rcu_read_lock(). The mon_config helpers
> send multiple IPIs, take the cpus_read_lock() in these cases.
>
> The other filesystem list walkers need to be able to sleep.
> Add cpus_read_lock() to rdtgroup_kn_lock_live() so that the
> cpuhp callbacks can't be invoked when file system operations are
> occurring.
>
> Add lockdep_assert_cpus_held() in the cases where the
> rdtgroup_kn_lock_live() call isn't obvious.
>
> Resctrl's domain online/offline calls now need to take the
> rdtgroup_mutex themselves.
>
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v2:
>  * Reworded a comment,
>  * Added a lockdep assertion
>  * Moved clear_closid_rmid() outside the locked region of cpu
>    online/offline
>
> Changes since v3:
>  * Added a header include
> ---
>  arch/x86/kernel/cpu/resctrl/core.c        | 38 +++++++++-----
>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 16 ++++--
>  arch/x86/kernel/cpu/resctrl/monitor.c     |  4 ++
>  arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  3 ++
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 63 ++++++++++++++++++++---
>  include/linux/resctrl.h                   |  2 +-
>  6 files changed, 100 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index edc0dd123317..f106c68a9be8 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -25,8 +25,15 @@
>  #include <asm/resctrl.h>
>  #include "internal.h"
>
> -/* Mutex to protect rdtgroup access. */
> -DEFINE_MUTEX(rdtgroup_mutex);
> +/*
> + * rdt_domain structures are kfree()d when their last CPU goes offline,
> + * and allocated when the first CPU in a new domain comes online.
> + * The rdt_resource's domain list is updated when this happens. Readers of
> + * the domain list must either take cpus_read_lock(), or rely on an RCU
> + * read-side critical section, to avoid observing concurrent modification.
> + * All writers take this mutex:
> + */
> +static DEFINE_MUTEX(domain_list_lock);
>
>  /*
>   * The cached resctrl_pqr_state is strictly per CPU and can never be
> @@ -508,6 +515,8 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
>         struct rdt_domain *d;
>         int err;
>
> +       lockdep_assert_held(&domain_list_lock);
> +
>         d = rdt_find_domain(r, id, &add_pos);
>         if (IS_ERR(d)) {
>                 pr_warn("Couldn't find cache id for CPU %d\n", cpu);
> @@ -541,11 +550,12 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
>                 return;
>         }
>
> -       list_add_tail(&d->list, add_pos);
> +       list_add_tail_rcu(&d->list, add_pos);
>
>         err = resctrl_online_domain(r, d);
>         if (err) {
> -               list_del(&d->list);
> +               list_del_rcu(&d->list);
> +               synchronize_rcu();
>                 domain_free(hw_dom);
>         }
>  }
> @@ -556,6 +566,8 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
>         struct rdt_hw_domain *hw_dom;
>         struct rdt_domain *d;
>
> +       lockdep_assert_held(&domain_list_lock);
> +
>         d = rdt_find_domain(r, id, NULL);
>         if (IS_ERR_OR_NULL(d)) {
>                 pr_warn("Couldn't find cache id for CPU %d\n", cpu);
> @@ -566,7 +578,8 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
>         cpumask_clear_cpu(cpu, &d->cpu_mask);
>         if (cpumask_empty(&d->cpu_mask)) {
>                 resctrl_offline_domain(r, d);
> -               list_del(&d->list);
> +               list_del_rcu(&d->list);
> +               synchronize_rcu();
>
>                 /*
>                  * rdt_domain "d" is going to be freed below, so clear
> @@ -594,30 +607,29 @@ static void clear_closid_rmid(int cpu)
>  static int resctrl_arch_online_cpu(unsigned int cpu)
>  {
>         struct rdt_resource *r;
> -       int ret;
>
> -       mutex_lock(&rdtgroup_mutex);
> +       mutex_lock(&domain_list_lock);
>         for_each_capable_rdt_resource(r)
>                 domain_add_cpu(cpu, r);
> +       mutex_unlock(&domain_list_lock);
> +
>         clear_closid_rmid(cpu);
>
> -       ret = resctrl_online_cpu(cpu);
> -       mutex_unlock(&rdtgroup_mutex);
> -
> -       return ret;
> +       return resctrl_online_cpu(cpu);
>  }
>
>  static int resctrl_arch_offline_cpu(unsigned int cpu)
>  {
>         struct rdt_resource *r;
>
> -       mutex_lock(&rdtgroup_mutex);
>         resctrl_offline_cpu(cpu);
>
> +       mutex_lock(&domain_list_lock);
>         for_each_capable_rdt_resource(r)
>                 domain_remove_cpu(cpu, r);
> +       mutex_unlock(&domain_list_lock);
> +
>         clear_closid_rmid(cpu);
> -       mutex_unlock(&rdtgroup_mutex);
>
>         return 0;
>  }
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index 280d66fae21c..d8d7c127403b 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -209,6 +209,9 @@ static int parse_line(char *line, struct resctrl_schema *s,
>         struct rdt_domain *d;
>         unsigned long dom_id;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP &&
>             (r->rid == RDT_RESOURCE_MBA || r->rid == RDT_RESOURCE_SMBA)) {
>                 rdt_last_cmd_puts("Cannot pseudo-lock MBA resource\n");
> @@ -313,6 +316,9 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
>         struct rdt_domain *d;
>         u32 idx;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
>                 return -ENOMEM;
>
> @@ -378,11 +384,9 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
>                 return -EINVAL;
>         buf[nbytes - 1] = '\0';
>
> -       cpus_read_lock();
>         rdtgrp = rdtgroup_kn_lock_live(of->kn);
>         if (!rdtgrp) {
>                 rdtgroup_kn_unlock(of->kn);
> -               cpus_read_unlock();
>                 return -ENOENT;
>         }
>         rdt_last_cmd_clear();
> @@ -444,7 +448,6 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
>  out:
>         rdt_staged_configs_clear();
>         rdtgroup_kn_unlock(of->kn);
> -       cpus_read_unlock();
>         return ret ?: nbytes;
>  }
>
> @@ -464,6 +467,9 @@ static void show_doms(struct seq_file *s, struct resctrl_schema *schema, int clo
>         bool sep = false;
>         u32 ctrl_val;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         seq_printf(s, "%*s:", max_name_width, schema->name);
>         list_for_each_entry(dom, &r->domains, list) {
>                 if (sep)
> @@ -534,8 +540,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  {
>         int cpu;
>
> -       /* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */
> -       lockdep_assert_held(&rdtgroup_mutex);
> +       /* When picking a cpu from cpu_mask, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
>
>         /*
>          * setup the parameters to pass to mon_event_count() to read the data.
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index ae02185f3354..41b4cd2c7d64 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -15,6 +15,7 @@
>   * Software Developer Manual June 2016, volume 3, section 17.17.
>   */
>
> +#include <linux/cpu.h>
>  #include <linux/module.h>
>  #include <linux/sizes.h>
>  #include <linux/slab.h>
> @@ -476,6 +477,9 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>
>         lockdep_assert_held(&rdtgroup_mutex);
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
>
>         entry->busy = 0;
> diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> index 460421051abf..fc3ed917d173 100644
> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> @@ -830,6 +830,9 @@ bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_domain *d)
>         struct rdt_domain *d_i;
>         bool ret = false;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         if (!zalloc_cpumask_var(&cpu_with_psl, GFP_KERNEL))
>                 return true;
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 3a8e2c98b611..9002ac728001 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -35,6 +35,10 @@
>  DEFINE_STATIC_KEY_FALSE(rdt_enable_key);
>  DEFINE_STATIC_KEY_FALSE(rdt_mon_enable_key);
>  DEFINE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
> +
> +/* Mutex to protect rdtgroup access. */
> +DEFINE_MUTEX(rdtgroup_mutex);
> +
>  static struct kernfs_root *rdt_root;
>  struct rdtgroup rdtgroup_default;
>  LIST_HEAD(rdt_all_groups);
> @@ -950,7 +954,8 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
>
>         mutex_lock(&rdtgroup_mutex);
>         hw_shareable = r->cache.shareable_bits;
> -       list_for_each_entry(dom, &r->domains, list) {
> +       rcu_read_lock();
> +       list_for_each_entry_rcu(dom, &r->domains, list) {
>                 if (sep)
>                         seq_putc(seq, ';');
>                 sw_shareable = 0;
> @@ -1006,8 +1011,10 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
>                 }
>                 sep = true;
>         }
> +       rcu_read_unlock();
>         seq_putc(seq, '\n');
>         mutex_unlock(&rdtgroup_mutex);
> +
>         return 0;
>  }
>
> @@ -1250,6 +1257,9 @@ static bool rdtgroup_mode_test_exclusive(struct rdtgroup *rdtgrp)
>         struct rdt_domain *d;
>         u32 ctrl;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         list_for_each_entry(s, &resctrl_schema_all, list) {
>                 r = s->res;
>                 if (r->rid == RDT_RESOURCE_MBA || r->rid == RDT_RESOURCE_SMBA)
> @@ -1516,6 +1526,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
>         struct rdt_domain *dom;
>         bool sep = false;
>
> +       cpus_read_lock();
>         mutex_lock(&rdtgroup_mutex);
>
>         list_for_each_entry(dom, &r->domains, list) {
> @@ -1532,6 +1543,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
>         seq_puts(s, "\n");
>
>         mutex_unlock(&rdtgroup_mutex);
> +       cpus_read_unlock();
>
>         return 0;
>  }
> @@ -1623,6 +1635,9 @@ static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
>         struct rdt_domain *d;
>         int ret = 0;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>  next:
>         if (!tok || tok[0] == '\0')
>                 return 0;
> @@ -1664,6 +1679,7 @@ static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of,
>         if (nbytes == 0 || buf[nbytes - 1] != '\n')
>                 return -EINVAL;
>
> +       cpus_read_lock();
>         mutex_lock(&rdtgroup_mutex);
>
>         rdt_last_cmd_clear();
> @@ -1673,6 +1689,7 @@ static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of,
>         ret = mon_config_write(r, buf, QOS_L3_MBM_TOTAL_EVENT_ID);
>
>         mutex_unlock(&rdtgroup_mutex);
> +       cpus_read_unlock();
>
>         return ret ?: nbytes;
>  }
> @@ -1688,6 +1705,7 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
>         if (nbytes == 0 || buf[nbytes - 1] != '\n')
>                 return -EINVAL;
>
> +       cpus_read_lock();
>         mutex_lock(&rdtgroup_mutex);
>
>         rdt_last_cmd_clear();
> @@ -1697,6 +1715,7 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
>         ret = mon_config_write(r, buf, QOS_L3_MBM_LOCAL_EVENT_ID);
>
>         mutex_unlock(&rdtgroup_mutex);
> +       cpus_read_unlock();
>
>         return ret ?: nbytes;
>  }
> @@ -2149,6 +2168,9 @@ static int set_cache_qos_cfg(int level, bool enable)
>         struct rdt_domain *d;
>         int cpu;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         if (level == RDT_RESOURCE_L3)
>                 update = l3_qos_cfg_update;
>         else if (level == RDT_RESOURCE_L2)
> @@ -2337,6 +2359,7 @@ struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn)
>         atomic_inc(&rdtgrp->waitcount);
>         kernfs_break_active_protection(kn);
>
> +       cpus_read_lock();
>         mutex_lock(&rdtgroup_mutex);
>
>         /* Was this group deleted while we waited? */
> @@ -2354,6 +2377,7 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
>                 return;
>
>         mutex_unlock(&rdtgroup_mutex);
> +       cpus_read_unlock();
>
>         if (atomic_dec_and_test(&rdtgrp->waitcount) &&
>             (rdtgrp->flags & RDT_DELETED)) {
> @@ -2651,6 +2675,9 @@ static int reset_all_ctrls(struct rdt_resource *r)
>         struct rdt_domain *d;
>         int i;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
>                 return -ENOMEM;
>
> @@ -2935,6 +2962,9 @@ static int mkdir_mondata_subdir_alldom(struct kernfs_node *parent_kn,
>         struct rdt_domain *dom;
>         int ret;
>
> +       /* Walking r->domains, ensure it can't race with cpuhp */
> +       lockdep_assert_cpus_held();
> +
>         list_for_each_entry(dom, &r->domains, list) {
>                 ret = mkdir_mondata_subdir(parent_kn, dom, r, prgrp);
>                 if (ret)
> @@ -3625,7 +3655,8 @@ static void domain_destroy_mon_state(struct rdt_domain *d)
>         kfree(d->mbm_local);
>  }
>
> -void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
> +static void _resctrl_offline_domain(struct rdt_resource *r,
> +                                   struct rdt_domain *d)
>  {
>         lockdep_assert_held(&rdtgroup_mutex);
>
> @@ -3660,6 +3691,13 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
>         domain_destroy_mon_state(d);
>  }
>
> +void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
> +{
> +       mutex_lock(&rdtgroup_mutex);
> +       _resctrl_offline_domain(r, d);
> +       mutex_unlock(&rdtgroup_mutex);
> +}
> +
>  static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
>  {
>         u32 idx_limit = resctrl_arch_system_num_rmid_idx();
> @@ -3691,7 +3729,7 @@ static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
>         return 0;
>  }
>
> -int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
> +static int _resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>  {
>         int err;
>
> @@ -3727,12 +3765,23 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>         return 0;
>  }
>
> +int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
> +{
> +       int err;
> +
> +       mutex_lock(&rdtgroup_mutex);
> +       err = _resctrl_online_domain(r, d);
> +       mutex_unlock(&rdtgroup_mutex);
> +
> +       return err;
> +}
> +
>  int resctrl_online_cpu(unsigned int cpu)
>  {
> -       lockdep_assert_held(&rdtgroup_mutex);
> -
> +       mutex_lock(&rdtgroup_mutex);
>         /* The cpu is set in default rdtgroup after online. */
>         cpumask_set_cpu(cpu, &rdtgroup_default.cpu_mask);
> +       mutex_unlock(&rdtgroup_mutex);
>
>         return 0;
>  }
> @@ -3753,8 +3802,7 @@ void resctrl_offline_cpu(unsigned int cpu)
>         struct rdtgroup *rdtgrp;
>         struct rdt_resource *l3 = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>
> -       lockdep_assert_held(&rdtgroup_mutex);
> -
> +       mutex_lock(&rdtgroup_mutex);
>         list_for_each_entry(rdtgrp, &rdt_all_groups, rdtgroup_list) {
>                 if (cpumask_test_and_clear_cpu(cpu, &rdtgrp->cpu_mask)) {
>                         clear_childcpus(rdtgrp, cpu);
> @@ -3774,6 +3822,7 @@ void resctrl_offline_cpu(unsigned int cpu)
>                         cqm_setup_limbo_handler(d, 0, cpu);
>                 }
>         }
> +       mutex_unlock(&rdtgroup_mutex);
>  }
>
>  /*
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index c4be3453b3ff..fe94ef3369fa 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -159,7 +159,7 @@ struct resctrl_schema;
>   * @cache_level:       Which cache level defines scope of this resource
>   * @cache:             Cache allocation related data
>   * @membw:             If the component has bandwidth controls, their properties.
> - * @domains:           All domains for this resource
> + * @domains:           RCU list of all domains for this resource
>   * @name:              Name to use in "schemata" file.
>   * @data_width:                Character width of data when displaying
>   * @default_ctrl:      Specifies default cache cbm or memory B/W percent.
> --
> 2.39.2
>

Re: [PATCH v4 24/24] x86/resctrl: Separate arch and fs resctrl locks

[James Morse]

Hi Peter,

On 13/06/2023 10:15, Peter Newman wrote:
> On Thu, May 25, 2023 at 8:03 PM James Morse <james.morse@arm.com> wrote:
>>
>> resctrl has one mutex that is taken by the architecture specific code,
>> and the filesystem parts. The two interact via cpuhp, where the
>> architecture code updates the domain list. Filesystem handlers that
>> walk the domains list should not run concurrently with the cpuhp
>> callback modifying the list.
>>
>> Exposing a lock from the filesystem code means the interface is not
>> cleanly defined, and creates the possibility of cross-architecture
>> lock ordering headaches. The interaction only exists so that certain
>> filesystem paths are serialised against cpu hotplug. The cpu hotplug
>> code already has a mechanism to do this using cpus_read_lock().
>>
>> MPAM's monitors have an overflow interrupt, so it needs to be possible
>> to walk the domains list in irq context. RCU is ideal for this,
>> but some paths need to be able to sleep to allocate memory.
> 
> I noticed there's also a call to get_domain_from_cpu() in
> rdt_ctrl_update(), which is invoked by IPI when updating a schemata
> file, but at least it's a blocking IPI and the caller holds the
> rdtgroup_mutex, so the handler is serialized with CPU hotplug.

resctrl_arch_update_domains()? This also has lockdep_assert_cpus_held(), which is taken by
rdtgroup_kn_lock_live() - this pattern covers all the user-space filesystem operations.

I'd really like to get all the resctrl_arch_* helpers away from depending on
rdtgroup_mutex. Part of this is to allow perf/kvm/etc to use this interface without having
to expose more things from resctrl.


> Taking a step back, I'm concerned about the scalability of searching
> these linked-lists of domains in atomic contexts. We already have
> machines where the list is 32 entries deep in L3, and much larger in
> L2 CAT.

(Isn't this an existing problem? All I'm doing here is making it something explicitly
supported).


> Will the overflow interrupt target a CPU in the correct domain? The
> existing domain list search in rdt_ctrl_update() is for the current
> CPU's domain, so an alternative there would be to store each CPU's
> interrupt-relevant domain pointers in percpu data for quick lookup.

For the overflow interrupt, the irqchip code passes the device to the irq handler, which
corresponds to the MSC and via some intermediate structure, the resctrl domain. So this is
cheap to look up.

The need to 'walk the list in IRQ context' really comes from perf, regardless of whether
the overflow interrupt is supported. The domain_id is cached, but the domain may go
offline before the PMU driver is next called, hence the need to search the list and check
the CPU each time. If this proves to be a bottleneck, we can look for a better data structure.
The domain list is sorted, so a bisect search would improve matters.
A hash table may work for x86, as far as I can see the cache-ids are where the domain-id
always comes from, and those values are picked by the kernel to be contiguous. (on arm64
they come from a firmware table, all we know is they should be unique).

resctrl_arch_find_domain() is a per-arch thing, so we can do whatever is best for each
architecture.


For your resctrl_arch_update_domains() example, x86 could dispatch an IPI to each CPU,
passing the necessary domain in msr_param as part of the main loop. This would be slower
for the caller as you'd have to wait for each one to complete, but it would avoid a CPU in
each domain having to search the domain list with interrupts masked. (possibly all at the
same time)
I figure schema updates are rare, and it doesn't matter how long they take, provided it
doesn't impact other tasks.


> Also, how quickly does the overflow condition need to be serviced? On
> Intel, overflow handling deadlines aren't even tight enough to warrant
> an interrupt handler.

Ultimately, I don't know. It's something the architecture supports, I think its most
useful for use with perf-record. I've not had anyone ask for this support yet.

MPAM can have bandwidth counters as small as 32bit and can count in bytes. If someone
builds this configuration, they may find the overflow interrupt goes off more frequently
than the overflow thread runs to scrub the counters.

MPAM also has options to scale the counters by some implementation specific size, as well
as 44 and 63 bit counters - all of which should overflow less frequently.

As with everything in the arm world, its very much "chose your own adventure".


Thanks,

James

Re: [PATCH v4 24/24] x86/resctrl: Separate arch and fs resctrl locks

[Reinette Chatre]

Hi James,

On 5/25/2023 11:02 AM, James Morse wrote:
> resctrl has one mutex that is taken by the architecture specific code,
> and the filesystem parts. The two interact via cpuhp, where the
> architecture code updates the domain list. Filesystem handlers that
> walk the domains list should not run concurrently with the cpuhp
> callback modifying the list.
> 
> Exposing a lock from the filesystem code means the interface is not
> cleanly defined, and creates the possibility of cross-architecture
> lock ordering headaches. The interaction only exists so that certain
> filesystem paths are serialised against cpu hotplug. The cpu hotplug
> code already has a mechanism to do this using cpus_read_lock().
> 
> MPAM's monitors have an overflow interrupt, so it needs to be possible
> to walk the domains list in irq context. RCU is ideal for this,
> but some paths need to be able to sleep to allocate memory.
> 
> Because resctrl_{on,off}line_cpu() take the rdtgroup_mutex as part
> of a cpuhp callback, cpus_read_lock() must always be taken first.
> rdtgroup_schemata_write() already does this.
> 
> Most of the filesystem code's domain list walkers are currently
> protected by the rdtgroup_mutex taken in rdtgroup_kn_lock_live().
> The exceptions are rdt_bit_usage_show() and the mon_config helpers
> which take the lock directly.
> 
> Make the domain list protected by RCU. An architecture-specific
> lock prevents concurrent writers. rdt_bit_usage_show() can

This does not sound right to me. The domain list belongs to resctrl,
the filesystem, having an architecture specific lock protect it does
not seem like the right thing to do. Could this instead be a resctrl
owned lock that is hidden behind helpers for the architecture
code to add domains?

Reinette

Re: [PATCH v4 24/24] x86/resctrl: Separate arch and fs resctrl locks

[James Morse]

Hi Reinette,

On 15/06/2023 23:26, Reinette Chatre wrote:
> On 5/25/2023 11:02 AM, James Morse wrote:
>> resctrl has one mutex that is taken by the architecture specific code,
>> and the filesystem parts. The two interact via cpuhp, where the
>> architecture code updates the domain list. Filesystem handlers that
>> walk the domains list should not run concurrently with the cpuhp
>> callback modifying the list.
>>
>> Exposing a lock from the filesystem code means the interface is not
>> cleanly defined, and creates the possibility of cross-architecture
>> lock ordering headaches. The interaction only exists so that certain
>> filesystem paths are serialised against cpu hotplug. The cpu hotplug
>> code already has a mechanism to do this using cpus_read_lock().
>>
>> MPAM's monitors have an overflow interrupt, so it needs to be possible
>> to walk the domains list in irq context. RCU is ideal for this,
>> but some paths need to be able to sleep to allocate memory.
>>
>> Because resctrl_{on,off}line_cpu() take the rdtgroup_mutex as part
>> of a cpuhp callback, cpus_read_lock() must always be taken first.
>> rdtgroup_schemata_write() already does this.
>>
>> Most of the filesystem code's domain list walkers are currently
>> protected by the rdtgroup_mutex taken in rdtgroup_kn_lock_live().
>> The exceptions are rdt_bit_usage_show() and the mon_config helpers
>> which take the lock directly.
>>
>> Make the domain list protected by RCU. An architecture-specific
>> lock prevents concurrent writers. rdt_bit_usage_show() can

> This does not sound right to me. The domain list belongs to resctrl,
> the filesystem,

I'd argue the list belongs to the arch code, as only the arch code writes to it.


> having an architecture specific lock protect it does
> not seem like the right thing to do. Could this instead be a resctrl
> owned lock that is hidden behind helpers for the architecture
> code to add domains?

resctrl should never be writing to the domain list, so it never needs to know how
concurrent-writers are avoided.

The memory is allocated and added to the list by the architecture code.
This new domain-list-lock API would only ever be called by the arch code, and there is no
resctrl call that needs to be made with that lock held. I don't see any reason for this to
be visible to the filesystem code.

I'm trying to keep the number of functions exposed by resctrl to the arch code as small as
possible. After all this they are:
resctrl_online_domain()
resctrl_offline_domain()
resctrl_online_cpu()
resctrl_offline_cpu()
resctrl_init()
resctrl_exit()

The weird one is resctrl_get_domain_from_cpu(), which is used by both architecture and
filesystem code, because I wanted to avoid duplicating it. It ends up inlined from a
header file.

Part of this is to explore making resctrl a loadable module in the future, which I think
fits with Tony Luck's aims.


Thanks,

James

RE: [PATCH v4 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking

[Shaopeng Tan (Fujitsu)]

Hello,

I ran resctrl selftest on Intel(R) Xeon(R) Gold 6254 CPU with nohz_full enabled/disabled,
it seems there is no problem.

<tested-by:tan.shaopeng@jp.fujitsu.com>

Re: [PATCH v4 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking

[James Morse]

Hi Shaopeng Tan

On 13/06/2023 07:18, Shaopeng Tan (Fujitsu) wrote:
> I ran resctrl selftest on Intel(R) Xeon(R) Gold 6254 CPU with nohz_full enabled/disabled,
> it seems there is no problem.

Thanks for your help with the testing!


James

Re: [PATCH v4 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking

[Reinette Chatre]

Hi James,

On 5/25/2023 11:01 AM, James Morse wrote:
> 
> The second part of this series adds a domain_list_lock to protect writes to the
> domain list, and protects the domain list with RCU - or read_cpus_lock().

read_cpus_lock() -> cpus_read_lock()

> 
> Use of RCU is to allow lockless readers of the domain list, today resctrl only has
> one, rdt_bit_usage_show(). But to get MPAMs monitors working, its very likely

This may need an update to reflect changes since initial version (similar to the
relevant patch).

Reinette