[PATCH V5 0/4] x86/resctrl: Enable user to view and select thread throttling mode

[PATCH V5 0/4] x86/resctrl: Enable user to view and select thread throttling mode

[Reinette Chatre]

V4 upstream submission available from:
https://lore.kernel.org/lkml/cover.1589652468.git.reinette.chatre@intel.com

Patches apply against x86/cache branch commit 0c4d5ba1b998e of tip repo at
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

Changes since V4:
- Pick up Babu's "Reviewed-by" tags.
- Three checks are performed before the MBA_CFG register is updated from
  its cache. Move all checks to the same if statement. (Babu)
- Remove unnecessary return statement when there is only a switch statement
  in the function that is already handling all cases. (Babu)
- Remove "mode" local variable from rdtgroup_mode_write(). This variable
  was previously used to create shorter lines with the original strcmp()
  code that was removed in patch 4/4.
- Andy pointed out that the repeated assignment to rdtgrp->mode could be
  replaced by a single assignment after all the checks. This was initially
  rejected because it would let the "RDT_MODE_PSEUDO_LOCKED" assignment
  slip through. Even so, Andy's feedback revealed that the new changes
  unintentionally let a user's attempt at setting the mode to pseudo-locked
  be silently ignored where it previously reported an error. Restore original
  user space behavior by returning success when user attempts to change any
  mode when it is already the current mode (including pseudo-locked) and
  returning failure when user attempts to set the mode to pseudo-locked.
  After this change it is possible to follow Andy's original suggestion
  of using a single assignment. (Andy)

V3 upstream submission available from:
https://lore.kernel.org/lkml/cover.1588808537.git.reinette.chatre@intel.com

Patches apply against x86/cache branch of tip repo at
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

Changes since V3:
- Maintain the thread throttling mode as a property ("arch_throttle_mode")
  of the memory bandwidth allocation resource
  instead of calling a function that queries the system's model each time
  this information is needed. Use this new property generically throughout
  with the goal of being independent of architecture. (Babu)
- Remove "intel" from thread_throttle_mode_init_intel_rw() and
  thread_throttle_mode_init_intel_ro() in anticipation of usage by other
  architectures.
- Use function parameter to update_mba_cfg() directly instead of having
  local variable point to it. (Fenghua)
- Remove unnecessary additional check whether platform supports feature
  from the "thread_throttle_mode" callback. The file will only be
  accessible on platforms that support the feature.
- Rework commit message of first patch to be more complete regarding
  support of all architectures after incorporating AMD feedback.
- View the thread throttle mode with rdtgroup mutex held since it is using
  cached information that may be changed concurrently.
- Remove unnecessary empty line. (Babu)

V2 upstream submission available from:
https://lore.kernel.org/lkml/cover.1586801373.git.reinette.chatre@intel.com

Changes since V2:
- Rebase on top of recently merged series "x86/resctrl: Support wider
  MBM counters". Small change needed to take into account
  asm/resctrl_sched.h -> asm/resctrl.h name change.
- Fix rST formatting of documentation (resctrl_ui.rst) describing
  new "thread_throttle_mode" resctrl file.
- Use boot_cpu_has() instead of static_cpu_has() when determining what
  to display to user (slow path).

V1 upstream submission available from:
https://lore.kernel.org/lkml/cover.1585765499.git.reinette.chatre@intel.com

A notable change since V1 is the inclusion of two additional patches from
Fenghua Yu that introduce the new per-thread MBA feature. These changes are
added to this series because they are small and closely related to the
original submission. The per-thread MBA feature is a hardware advancement
that requires no software interface changes. The patches added just enumerate
the feature and expose it to userspace by showing "per-thread" in the new
resctrl file "thread_throttle_mode" to help user applications fine tune
performance.

There are currently a few resctrl changes outstanding for upstream inclusion.
To support their consideration all outstanding resctrl patches can be
viewed at https://github.com/rchatre/linux.git (branch resctrl/next)

Changes since V1 (also documented within patches to which they apply):
- Rebased on top of James Morse's CDP fix
(https://lore.kernel.org/lkml/20200221162105.154163-1-james.morse@arm.com)
- Remove RF_UNINITIALIZED (having uninitialized be represented with ones
  creates too much confusion), replace with an explicit check of rft->fflags
  in rdtgroup_add_files() (Fenghua Yu)
- Rename MBA_THREAD_THROTTLE_MODE to MBA_THROTTLE_MODE_MASK to clarify its
  use as a mask (Tony Luck)
- Introduce explicit MBA_THROTTLE_MODE_MAX instead of implying it is the
  opposite of min and use these values (min and max) explicitly whenever
  testing/setting the throttle mode value (Tony Luck)
- Add __init attribute to thread_throttle_mode_init_intel_rw() and
  thread_throttle_mode_init_intel_ro() since they are only needed during
  initialization (Fenghua Yu)
- Remove MBA_CFG MSR reads and error checking so that the patch is simpler
  and easier to review (Fenghua Yu)
- Ensure CPU hotplug lock is taken when writing register on multiple CPUs (Fenghua Yu)
- Use CPU mask already maintained as part of domains to determine which
  CPUs to update MBA register on (Fenghua Yu)
- Maintain MBA configuration register contents to support use case when not
  all CPUs of a package are online when configuration is set from user
  space
- Use seq_puts() instead of seq_printf() when simple strings are printed
- Set MBA configuration to default when resctrl is unmounted
- Complete rewrite of "thread_throttle_mode" documentation (Tony Luck)
- Remove unnecessary checks on user input (Andy Shevchenko)
- Change code style surrounding usage of sysfs_match_string() (Andy Shevchenko)

From V1 submission:

The first patch in this series introduces a new resctrl file,
"thread_throttle_mode", on Intel systems that exposes to the
user how per-thread values are allocated to a core. This is added in
support of newer Intel systems that can be configured to allocate
either maximum or minimum throttling of the per-thread CLOS values
to the core.

Details about the feature can be found in the commit description and
in Chapter 9 of the most recent Intel ISE available from
https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf

The first patch parses user input with the appropriate sysfs API that has
not previously been used in resctrl. The second (later in the fourth) patch is
added as a subsequent cleanup that switches existing resctrl string parsing
code to also use this appropriate API.



Fenghua Yu (2):
  x86/resctrl: Enumerate per-thread MBA
  x86/resctrl: Enable per-thread MBA

Reinette Chatre (2):
  x86/resctrl: Enable user to view and select thread throttling mode
  x86/resctrl: Use appropriate API for strings terminated by newline

 Documentation/x86/resctrl_ui.rst       |  22 ++-
 arch/x86/include/asm/cpufeatures.h     |   1 +
 arch/x86/kernel/cpu/cpuid-deps.c       |   1 +
 arch/x86/kernel/cpu/resctrl/core.c     |  52 ++++++
 arch/x86/kernel/cpu/resctrl/internal.h |  49 ++++-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 247 +++++++++++++++++++++++--
 arch/x86/kernel/cpu/scattered.c        |   1 +
 7 files changed, 345 insertions(+), 28 deletions(-)

-- 
2.21.0

[PATCH V5 1/4] x86/resctrl: Enable user to view and select thread throttling mode

[Reinette Chatre]

Intel Memory Bandwidth Allocation (MBA) control is provided per
processor core. At the same time different CLOS, configured with
different bandwidth percentages, can be assigned to the hardware
threads sharing a core. In the original implementation of MBA the
maximum throttling of the per-thread CLOS is allocated to the core.
Specifically, the lower bandwidth percentage is allocated to the core.

Newer systems can be configured to allocate either maximum or
minimum throttling of the per-thread CLOS values to the core.

Introduce a new resctrl file, "thread_throttle_mode", on Intel systems
that exposes to the user how per-thread values are allocated to
a core. On systems that support the original MBA implementation the
file will always display "max". On systems that can be configured
the possible values are "min" or "max" that the user can modify by
writing these same words to the file.

AMD confirmed in
https://lore.kernel.org/lkml/18d277fd-6523-319c-d560-66b63ff606b8@amd.com
that AMD bandwidth allocation is already at thread level. But AMD does not
use memory delay throttle model to control the allocation like Intel does.
So, to avoid any confusion the thread throttling mode would be UNDEFINED
on AMD systems and the "thread_throttle_mode" file will not be visible.

Cc: Babu Moger <babu.moger@amd.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes since V4:
- Three checks are performed before the MBA_CFG register is updated from
  its cache. Move all checks to the same if statement. (Babu)
- Remove unnecessary return statement when there is only a switch statement
  in the function that is already handling all cases. (Babu)

 Documentation/x86/resctrl_ui.rst       |  19 ++-
 arch/x86/kernel/cpu/resctrl/core.c     |  49 +++++++
 arch/x86/kernel/cpu/resctrl/internal.h |  47 +++++-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 196 ++++++++++++++++++++++++-
 4 files changed, 302 insertions(+), 9 deletions(-)

diff --git a/Documentation/x86/resctrl_ui.rst b/Documentation/x86/resctrl_ui.rst
index 5368cedfb530..861ee2816470 100644
--- a/Documentation/x86/resctrl_ui.rst
+++ b/Documentation/x86/resctrl_ui.rst
@@ -138,6 +138,19 @@ with respect to allocation:
 		non-linear. This field is purely informational
 		only.
 
+"thread_throttle_mode":
+		Indicator (on some CPU models control) on Intel systems
+		of how tasks running on threads of a physical core are
+		throttled in cases where they request different memory
+		bandwidth percentages:
+
+		"min":
+			the largest percentage is applied
+			to all threads
+		"max":
+			the smallest percentage is applied
+			to all threads
+
 If RDT monitoring is available there will be an "L3_MON" directory
 with the following files:
 
@@ -364,8 +377,10 @@ to the next control step available on the hardware.
 
 The bandwidth throttling is a core specific mechanism on some of Intel
 SKUs. Using a high bandwidth and a low bandwidth setting on two threads
-sharing a core will result in both threads being throttled to use the
-low bandwidth. The fact that Memory bandwidth allocation(MBA) is a core
+sharing a core may result in both threads being throttled to use the
+low bandwidth (see "thread_throttle_mode").
+
+The fact that Memory bandwidth allocation(MBA) may be a core
 specific mechanism where as memory bandwidth monitoring(MBM) is done at
 the package level may lead to confusion when users try to apply control
 via the MBA and then monitor the bandwidth to see if the controls are
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 12f967c6b603..687221cae5c3 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -250,6 +250,40 @@ static inline bool rdt_get_mb_table(struct rdt_resource *r)
 	return false;
 }
 
+/*
+ * Restore the MBA configuration from the cached configuration. Used for
+ * the case when an entire package was offline at the time the user made
+ * the configuration change.
+ */
+static void mba_cfg_reconfigure_throttle_mode(struct rdt_resource *r)
+{
+	if (r->alloc_capable && r == &rdt_resources_all[RDT_RESOURCE_MBA] &&
+	    r->membw.arch_throttle_mode == THREAD_THROTTLE_MIN_MAX)
+		wrmsrl(MSR_MBA_CFG, mba_cfg_msr);
+}
+
+/*
+ * Model-specific test to determine if platform where memory bandwidth
+ * control is applied to a core can be configured to apply either the
+ * maximum or minimum of the per-thread delay values.
+ * By default, platforms where memory bandwidth control is applied to a
+ * core will select the maximum delay value of the per-thread CLOS.
+ *
+ * NOTE: delay value programmed to hardware is inverse of bandwidth
+ * percentage configured via user interface.
+ */
+static bool mba_cfg_supports_min_max_intel(void)
+{
+	switch (boot_cpu_data.x86_model) {
+	case INTEL_FAM6_ATOM_TREMONT_D:
+	case INTEL_FAM6_ICELAKE_X:
+	case INTEL_FAM6_ICELAKE_D:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static bool __get_mem_config_intel(struct rdt_resource *r)
 {
 	union cpuid_0x10_3_eax eax;
@@ -270,6 +304,14 @@ static bool __get_mem_config_intel(struct rdt_resource *r)
 	}
 	r->data_width = 3;
 
+	if (mba_cfg_supports_min_max_intel()) {
+		r->membw.arch_throttle_mode = THREAD_THROTTLE_MIN_MAX;
+		thread_throttle_mode_init_rw();
+	} else {
+		r->membw.arch_throttle_mode = THREAD_THROTTLE_MAX_ONLY;
+		thread_throttle_mode_init_ro();
+	}
+
 	r->alloc_capable = true;
 	r->alloc_enabled = true;
 
@@ -289,6 +331,11 @@ static bool __rdt_get_mem_config_amd(struct rdt_resource *r)
 	/* AMD does not use delay */
 	r->membw.delay_linear = false;
 
+	/*
+	 * AMD does not use memory delay throttle model to control
+	 * the allocation like Intel does.
+	 */
+	r->membw.arch_throttle_mode = THREAD_THROTTLE_UNDEFINED;
 	r->membw.min_bw = 0;
 	r->membw.bw_gran = 1;
 	/* Max value is 2048, Data width should be 4 in decimal */
@@ -580,6 +627,8 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
 
 	rdt_domain_reconfigure_cdp(r);
 
+	mba_cfg_reconfigure_throttle_mode(r);
+
 	if (r->alloc_capable && domain_setup_ctrlval(r, d)) {
 		kfree(d);
 		return;
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index f20a47d120b1..6b9b21d67c9b 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -9,6 +9,7 @@
 
 #define MSR_IA32_L3_QOS_CFG		0xc81
 #define MSR_IA32_L2_QOS_CFG		0xc82
+#define MSR_MBA_CFG			0xc84
 #define MSR_IA32_L3_CBM_BASE		0xc90
 #define MSR_IA32_L2_CBM_BASE		0xd10
 #define MSR_IA32_MBA_THRTL_BASE		0xd50
@@ -21,6 +22,9 @@
 
 #define L2_QOS_CDP_ENABLE		0x01ULL
 
+#define MBA_THROTTLE_MODE_MIN		0x01ULL
+#define MBA_THROTTLE_MODE_MAX		0x00ULL
+
 /*
  * Event IDs are used to program IA32_QM_EVTSEL before reading event
  * counter from IA32_QM_CTR
@@ -38,6 +42,8 @@
 #define MBA_MAX_MBPS			U32_MAX
 #define MAX_MBA_BW_AMD			0x800
 
+#define MBA_THROTTLE_MODE_MASK		BIT_ULL(0)
+
 #define RMID_VAL_ERROR			BIT_ULL(63)
 #define RMID_VAL_UNAVAIL		BIT_ULL(62)
 /*
@@ -47,6 +53,10 @@
  */
 #define MBM_CNTR_WIDTH_OFFSET_MAX (62 - MBM_CNTR_WIDTH_BASE)
 
+/*
+ * MSR_MBA_CFG cache
+ */
+extern u64 mba_cfg_msr;
 
 struct rdt_fs_context {
 	struct kernfs_fs_context	kfc;
@@ -368,6 +378,26 @@ struct rdt_cache {
 	unsigned int	shareable_bits;
 };
 
+/**
+ * enum membw_throttle_mode - System's memory bandwidth throttling mode
+ * @THREAD_THROTTLE_UNDEFINED:	Not relevant to the system
+ * @THREAD_THROTTLE_MIN_MAX:	Memory bandwidth is throttled at the core and
+ *				can be configured to use smallest or largest
+ *				bandwidth percentage assigned to threads.
+ *				Systems that support this mode will support
+ *				MSR_MBA_CFG and the configuration of
+ *				thread throttling mode via resctrl
+ *				file "thread_throttle_mode".
+ * @THREAD_THROTTLE_MAX_ONLY:	Memory bandwidth is throttled at the core
+ *				always using smallest bandwidth percentage
+ *				assigned to threads, aka "max throttling"
+ */
+enum membw_throttle_mode {
+	THREAD_THROTTLE_UNDEFINED = 0,
+	THREAD_THROTTLE_MIN_MAX,
+	THREAD_THROTTLE_MAX_ONLY,
+};
+
 /**
  * struct rdt_membw - Memory bandwidth allocation related data
  * @max_delay:		Max throttle delay. Delay is the hardware
@@ -375,16 +405,19 @@ struct rdt_cache {
  * @min_bw:		Minimum memory bandwidth percentage user can request
  * @bw_gran:		Granularity at which the memory bandwidth is allocated
  * @delay_linear:	True if memory B/W delay is in linear scale
+ * @arch_throttle_mode:	Bandwidth throttling mode when threads request
+ *			different memory bandwidths
  * @mba_sc:		True if MBA software controller(mba_sc) is enabled
  * @mb_map:		Mapping of memory B/W percentage to memory B/W delay
  */
 struct rdt_membw {
-	u32		max_delay;
-	u32		min_bw;
-	u32		bw_gran;
-	u32		delay_linear;
-	bool		mba_sc;
-	u32		*mb_map;
+	u32				max_delay;
+	u32				min_bw;
+	u32				bw_gran;
+	u32				delay_linear;
+	enum membw_throttle_mode	arch_throttle_mode;
+	bool				mba_sc;
+	u32				*mb_map;
 };
 
 static inline bool is_llc_occupancy_enabled(void)
@@ -611,5 +644,7 @@ void __check_limbo(struct rdt_domain *d, bool force_free);
 bool cbm_validate_intel(char *buf, u32 *data, struct rdt_resource *r);
 bool cbm_validate_amd(char *buf, u32 *data, struct rdt_resource *r);
 void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
+void thread_throttle_mode_init_rw(void);
+void thread_throttle_mode_init_ro(void);
 
 #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index d7cb5ab0d1f0..3ce6319b7226 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -29,6 +29,7 @@
 
 #include <uapi/linux/magic.h>
 
+#include <asm/intel-family.h>
 #include <asm/resctrl.h>
 #include "internal.h"
 
@@ -38,6 +39,7 @@ DEFINE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
 static struct kernfs_root *rdt_root;
 struct rdtgroup rdtgroup_default;
 LIST_HEAD(rdt_all_groups);
+u64 mba_cfg_msr;
 
 /* Kernel fs node for "info" directory under root */
 static struct kernfs_node *kn_info;
@@ -1017,6 +1019,141 @@ static int max_threshold_occ_show(struct kernfs_open_file *of,
 	return 0;
 }
 
+/*
+ * As documented in the Intel SDM, on systems supporting the original MBA
+ * implementation the delay value allocated to a core is always the maximum
+ * of the delay values assigned to the hardware threads sharing the core.
+ *
+ * Some systems support a model-specific MSR with which this default
+ * behavior can be changed. On these systems the core can be allocated
+ * with either the minimum or maximum delay value assigned to its hardware
+ * threads.
+ *
+ * NOTE: The hardware deals with memory delay values that may be programmed
+ * from zero (implying zero delay, and full bandwidth available) to the
+ * maximum specified in CPUID. The software interface deals with memory
+ * bandwidth percentages that are the inverse of the delay values (100%
+ * memory bandwidth from user perspective is zero MBA delay from hardware
+ * perspective). When maximum throttling is active the core is allocated
+ * with the maximum delay value that from the software interface will be
+ * the minimum of the bandwidth percentages assigned to the hardware threads
+ * sharing the core.
+ */
+static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of,
+					 struct seq_file *seq, void *v)
+{
+	struct rdt_resource *r = of->kn->parent->priv;
+	unsigned int throttle_mode = 0;
+
+	mutex_lock(&rdtgroup_mutex);
+
+	if (r->membw.arch_throttle_mode == THREAD_THROTTLE_MIN_MAX)
+		throttle_mode = mba_cfg_msr & MBA_THROTTLE_MODE_MASK;
+
+	seq_puts(seq,
+		 throttle_mode == MBA_THROTTLE_MODE_MIN ? "min\n" : "max\n");
+
+	mutex_unlock(&rdtgroup_mutex);
+	return 0;
+}
+
+static void update_mba_cfg(void *data)
+{
+	wrmsrl(MSR_MBA_CFG, *(u64 *)data);
+}
+
+/*
+ * The model-specific MBA configuration MSR has package scope. Making a
+ * system-wide MBA configuration change thus needs to modify the MSR on one
+ * CPU from each package.
+ */
+static int rdt_system_mba_cfg_set(u64 mba_cfg)
+{
+	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA];
+	cpumask_var_t cpu_mask;
+	struct rdt_domain *d;
+
+	if (list_is_singular(&r->domains)) {
+		wrmsrl(MSR_MBA_CFG, mba_cfg);
+		goto out;
+	}
+
+	if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL)) {
+		rdt_last_cmd_puts("Memory allocation error\n");
+		return -ENOMEM;
+	}
+
+	list_for_each_entry(d, &r->domains, list)
+		cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);
+
+	on_each_cpu_mask(cpu_mask, update_mba_cfg, &mba_cfg, 1);
+
+	free_cpumask_var(cpu_mask);
+out:
+	mba_cfg_msr = mba_cfg;
+	return 0;
+}
+
+static void mba_cfg_reset_all(void)
+{
+	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA];
+
+	if (!r->alloc_capable)
+		return;
+
+	if (r->membw.arch_throttle_mode == THREAD_THROTTLE_MIN_MAX)
+		rdt_system_mba_cfg_set(0);
+}
+
+/*
+ * Callback will only be associated with the "thread_throttle_mode" file on
+ * systems that are capable of memory bandwidth allocation
+ * (RDT_RESOURCE_MBA is alloc_capable) AND the thread throttle mode is
+ * THREAD_THROTTLE_MIN_MAX.
+ *
+ * See NOTE associated with rdt_thread_throttle_mode_show() for
+ * details of the min/max interpretation.
+ */
+static ssize_t rdt_thread_throttle_mode_write(struct kernfs_open_file *of,
+					      char *buf, size_t nbytes,
+					      loff_t off)
+{
+	u64 mba_cfg;
+	int ret = 0;
+
+	if (nbytes == 0)
+		return -EINVAL;
+
+	cpus_read_lock();
+	mutex_lock(&rdtgroup_mutex);
+
+	rdt_last_cmd_clear();
+
+	mba_cfg = mba_cfg_msr & MBA_THROTTLE_MODE_MASK;
+
+	if ((sysfs_streq(buf, "min") && mba_cfg == MBA_THROTTLE_MODE_MIN) ||
+	    (sysfs_streq(buf, "max") && mba_cfg == MBA_THROTTLE_MODE_MAX))
+		goto out;
+
+	if (sysfs_streq(buf, "min")) {
+		mba_cfg = MBA_THROTTLE_MODE_MIN;
+	} else if (sysfs_streq(buf, "max")) {
+		mba_cfg = MBA_THROTTLE_MODE_MAX;
+	} else {
+		rdt_last_cmd_puts("Unknown or unsupported mode\n");
+		ret = -EINVAL;
+		goto out;
+	}
+
+	mba_cfg = (mba_cfg_msr & ~MBA_THROTTLE_MODE_MASK) | mba_cfg;
+	ret = rdt_system_mba_cfg_set(mba_cfg);
+
+out:
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+	return ret ?: nbytes;
+}
+
 static ssize_t max_threshold_occ_write(struct kernfs_open_file *of,
 				       char *buf, size_t nbytes, loff_t off)
 {
@@ -1512,6 +1649,16 @@ static struct rftype res_common_files[] = {
 		.seq_show	= rdt_delay_linear_show,
 		.fflags		= RF_CTRL_INFO | RFTYPE_RES_MB,
 	},
+	/*
+	 * Platform specific which (if any) capabilities are provided by
+	 * thread_throttle_mode. Defer some initialization to platform
+	 * discovery.
+	 */
+	{
+		.name		= "thread_throttle_mode",
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdt_thread_throttle_mode_show,
+	},
 	{
 		.name		= "max_threshold_occupancy",
 		.mode		= 0644,
@@ -1571,6 +1718,52 @@ static struct rftype res_common_files[] = {
 
 };
 
+static struct rftype *rdtgroup_rftype_by_name(const char *name)
+{
+	struct rftype *rfts, *rft;
+	int len;
+
+	rfts = res_common_files;
+	len = ARRAY_SIZE(res_common_files);
+
+	for (rft = rfts; rft < rfts + len; rft++) {
+		if (!strcmp(rft->name, name))
+			return rft;
+	}
+
+	return NULL;
+}
+
+/*
+ * Only systems that support memory bandwidth allocation and have
+ * THREAD_THROTTLE_MIN_MAX set will support a writable thread_throttle_mode
+ * file with which the user can modify the thread throttling mode.
+ */
+void __init thread_throttle_mode_init_rw(void)
+{
+	struct rftype *rft;
+
+	rft = rdtgroup_rftype_by_name("thread_throttle_mode");
+	if (!rft)
+		return;
+
+	rft->mode = 0644;
+	rft->write = rdt_thread_throttle_mode_write;
+	rft->fflags = RF_CTRL_INFO | RFTYPE_RES_MB;
+}
+
+void __init thread_throttle_mode_init_ro(void)
+{
+	struct rftype *rft;
+
+	rft = rdtgroup_rftype_by_name("thread_throttle_mode");
+	if (!rft)
+		return;
+
+	rft->mode = 0444;
+	rft->fflags = RF_CTRL_INFO | RFTYPE_RES_MB;
+}
+
 static int rdtgroup_add_files(struct kernfs_node *kn, unsigned long fflags)
 {
 	struct rftype *rfts, *rft;
@@ -1582,7 +1775,7 @@ static int rdtgroup_add_files(struct kernfs_node *kn, unsigned long fflags)
 	lockdep_assert_held(&rdtgroup_mutex);
 
 	for (rft = rfts; rft < rfts + len; rft++) {
-		if ((fflags & rft->fflags) == rft->fflags) {
+		if (rft->fflags && ((fflags & rft->fflags) == rft->fflags)) {
 			ret = rdtgroup_add_file(kn, rft);
 			if (ret)
 				goto error;
@@ -2371,6 +2564,7 @@ static void rdt_kill_sb(struct super_block *sb)
 	/*Put everything back to default values. */
 	for_each_alloc_enabled_rdt_resource(r)
 		reset_all_ctrls(r);
+	mba_cfg_reset_all();
 	cdp_disable_all();
 	rmdir_all_sub();
 	rdt_pseudo_lock_release();
-- 
2.21.0

[PATCH V5 2/4] x86/resctrl: Enumerate per-thread MBA

[Reinette Chatre]

From: Fenghua Yu <fenghua.yu@intel.com>

Some systems support per-thread Memory Bandwidth Allocation (MBA) which
applies a throttling delay value to each hardware thread instead of to
a core. Per-thread MBA is enumerated by CPUID.

No feature flag is shown in /proc/cpuinfo. User applications need to
check a resctrl throttling mode info file to know if the feature is
supported.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
---
Changes since V4:
- Pick up Babu's "Reviewed-by" tag.

 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/cpuid-deps.c   | 1 +
 arch/x86/kernel/cpu/scattered.c    | 1 +
 3 files changed, 3 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index db189945e9b0..d0ec26ce7f66 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -286,6 +286,7 @@
 #define X86_FEATURE_FENCE_SWAPGS_USER	(11*32+ 4) /* "" LFENCE in user entry SWAPGS path */
 #define X86_FEATURE_FENCE_SWAPGS_KERNEL	(11*32+ 5) /* "" LFENCE in kernel entry SWAPGS path */
 #define X86_FEATURE_SPLIT_LOCK_DETECT	(11*32+ 6) /* #AC for split lock */
+#define X86_FEATURE_PER_THREAD_MBA	(11*32+ 7) /* "" Per-thread Memory Bandwidth Allocation */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
 #define X86_FEATURE_AVX512_BF16		(12*32+ 5) /* AVX512 BFLOAT16 instructions */
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 3cbe24ca80ab..3e30b26c50ef 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -69,6 +69,7 @@ static const struct cpuid_dep cpuid_deps[] = {
 	{ X86_FEATURE_CQM_MBM_TOTAL,		X86_FEATURE_CQM_LLC   },
 	{ X86_FEATURE_CQM_MBM_LOCAL,		X86_FEATURE_CQM_LLC   },
 	{ X86_FEATURE_AVX512_BF16,		X86_FEATURE_AVX512VL  },
+	{ X86_FEATURE_PER_THREAD_MBA,		X86_FEATURE_MBA       },
 	{}
 };
 
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index 62b137c3c97a..bccfc9ff3cc1 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -35,6 +35,7 @@ static const struct cpuid_bit cpuid_bits[] = {
 	{ X86_FEATURE_CDP_L3,		CPUID_ECX,  2, 0x00000010, 1 },
 	{ X86_FEATURE_CDP_L2,		CPUID_ECX,  2, 0x00000010, 2 },
 	{ X86_FEATURE_MBA,		CPUID_EBX,  3, 0x00000010, 0 },
+	{ X86_FEATURE_PER_THREAD_MBA,	CPUID_ECX,  0, 0x00000010, 3 },
 	{ X86_FEATURE_HW_PSTATE,	CPUID_EDX,  7, 0x80000007, 0 },
 	{ X86_FEATURE_CPB,		CPUID_EDX,  9, 0x80000007, 0 },
 	{ X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
-- 
2.21.0

[PATCH V5 3/4] x86/resctrl: Enable per-thread MBA

[Reinette Chatre]

From: Fenghua Yu <fenghua.yu@intel.com>

Current Memory Bandwidth Allocation (MBA) hardware has a limitation:
all threads on the same core must have the same delay value. If there
are different delay values across threads on one core, the original
MBA implementation allocates the max delay value to the core and an
updated implementation allocates either min or max delay value specified
by a configuration MSR across threads on the core.

Newer systems support per-thread MBA such that each thread is allocated
with its own delay value.

If per-thread MBA is supported, report "per-thread" in resctrl file
"info/MB/thread_throttle_mode" to let user applications know memory
bandwidth is allocated per thread and help them fine tune MBA on thread
level.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
[reinette: transition patch to use membw_throttle_mode enum]
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
---
Changes since V4:
- Pick up Babu's "Reviewed-by" tag.

 Documentation/x86/resctrl_ui.rst       |  3 +++
 arch/x86/kernel/cpu/resctrl/core.c     |  5 ++++-
 arch/x86/kernel/cpu/resctrl/internal.h |  2 ++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 11 +++++++++++
 4 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/Documentation/x86/resctrl_ui.rst b/Documentation/x86/resctrl_ui.rst
index 861ee2816470..1b066d1aafad 100644
--- a/Documentation/x86/resctrl_ui.rst
+++ b/Documentation/x86/resctrl_ui.rst
@@ -150,6 +150,9 @@ with respect to allocation:
 		"max":
 			the smallest percentage is applied
 			to all threads
+		"per-thread":
+			bandwidth percentages are directly applied to
+			the threads running on the core
 
 If RDT monitoring is available there will be an "L3_MON" directory
 with the following files:
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 687221cae5c3..716ad71edf80 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -304,7 +304,10 @@ static bool __get_mem_config_intel(struct rdt_resource *r)
 	}
 	r->data_width = 3;
 
-	if (mba_cfg_supports_min_max_intel()) {
+	if (boot_cpu_has(X86_FEATURE_PER_THREAD_MBA)) {
+		r->membw.arch_throttle_mode = THREAD_THROTTLE_PER_THREAD;
+		thread_throttle_mode_init_ro();
+	} else if (mba_cfg_supports_min_max_intel()) {
 		r->membw.arch_throttle_mode = THREAD_THROTTLE_MIN_MAX;
 		thread_throttle_mode_init_rw();
 	} else {
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 6b9b21d67c9b..e198ea2a8468 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -391,11 +391,13 @@ struct rdt_cache {
  * @THREAD_THROTTLE_MAX_ONLY:	Memory bandwidth is throttled at the core
  *				always using smallest bandwidth percentage
  *				assigned to threads, aka "max throttling"
+ * @THREAD_THROTTLE_PER_THREAD:	Memory bandwidth is throttled at the thread
  */
 enum membw_throttle_mode {
 	THREAD_THROTTLE_UNDEFINED = 0,
 	THREAD_THROTTLE_MIN_MAX,
 	THREAD_THROTTLE_MAX_ONLY,
+	THREAD_THROTTLE_PER_THREAD,
 };
 
 /**
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 3ce6319b7226..088a1536bccc 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1038,6 +1038,11 @@ static int max_threshold_occ_show(struct kernfs_open_file *of,
  * with the maximum delay value that from the software interface will be
  * the minimum of the bandwidth percentages assigned to the hardware threads
  * sharing the core.
+ *
+ * Some systems (identified by X86_FEATURE_PER_THREAD_MBA enumerated via CPUID)
+ * support per-thread MBA. On these systems hardware doesn't apply the minimum
+ * or maximum delay value to all threads in a core. Instead, a thread is
+ * allocated with the delay value that is assigned to the thread.
  */
 static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of,
 					 struct seq_file *seq, void *v)
@@ -1047,12 +1052,18 @@ static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of,
 
 	mutex_lock(&rdtgroup_mutex);
 
+	if (r->membw.arch_throttle_mode == THREAD_THROTTLE_PER_THREAD) {
+		seq_puts(seq, "per-thread\n");
+		goto out;
+	}
+
 	if (r->membw.arch_throttle_mode == THREAD_THROTTLE_MIN_MAX)
 		throttle_mode = mba_cfg_msr & MBA_THROTTLE_MODE_MASK;
 
 	seq_puts(seq,
 		 throttle_mode == MBA_THROTTLE_MODE_MIN ? "min\n" : "max\n");
 
+out:
 	mutex_unlock(&rdtgroup_mutex);
 	return 0;
 }
-- 
2.21.0

[PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Reinette Chatre]

The user input to files in the resctrl filesystem are expected to be
terminated with a newline. Testing the user input includes a test for
the presence of a newline and then replacing the newline with NUL
byte followed by comparison using strcmp().

sysfs_streq() exists to test if strings are equal, treating both NUL and
newline-then-NUL as equivalent string terminations. Even more,
sysfs_match_string() exists to match a given string in an array using
sysfs_streq().

Replace existing strcmp() comparisons of strings that are terminated
with a newline with more appropriate sysfs_streq() via the
sysfs_match_string() API that can perform the match across the different
mode strings that are already maintained in an array.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes since V4:
- Remove "mode" local variable from rdtgroup_mode_write(). This variable
  was previously used to create shorter lines with the original strcmp()
  code that was removed in patch 4/4.
- Andy pointed out that the repeated assignment to rdtgrp->mode could be
  replaced by a single assignment after all the checks. This was initially
  rejected because it would let the "RDT_MODE_PSEUDO_LOCKED" assignment
  slip through. Even so, Andy's feedback revealed that the new changes
  unintentionally let a user's attempt at setting the mode to pseudo-locked
  be silently ignored where it previously reported an error. Restore original
  user space behavior by returning success when user attempts to change any
  mode when it is already the current mode (including pseudo-locked) and
  returning failure when user attempts to set the mode to pseudo-locked.
  After this change it is possible to follow Andy's original suggestion
  of using a single assignment. (Andy)

 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 40 ++++++++++++++------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 088a1536bccc..31f1bacaa288 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1414,13 +1414,11 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
 				   char *buf, size_t nbytes, loff_t off)
 {
 	struct rdtgroup *rdtgrp;
-	enum rdtgrp_mode mode;
-	int ret = 0;
+	int user_m;
+	int ret;
 
-	/* Valid input requires a trailing newline */
-	if (nbytes == 0 || buf[nbytes - 1] != '\n')
+	if (nbytes == 0)
 		return -EINVAL;
-	buf[nbytes - 1] = '\0';
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
 	if (!rdtgrp) {
@@ -1430,29 +1428,33 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
 
 	rdt_last_cmd_clear();
 
-	mode = rdtgrp->mode;
+	ret = sysfs_match_string(rdt_mode_str, buf);
+	if (ret < 0) {
+		rdt_last_cmd_puts("Unknown or unsupported mode\n");
+		ret = -EINVAL;
+		goto out;
+	}
+
+	user_m = ret;
+	ret = 0;
 
-	if ((!strcmp(buf, "shareable") && mode == RDT_MODE_SHAREABLE) ||
-	    (!strcmp(buf, "exclusive") && mode == RDT_MODE_EXCLUSIVE) ||
-	    (!strcmp(buf, "pseudo-locksetup") &&
-	     mode == RDT_MODE_PSEUDO_LOCKSETUP) ||
-	    (!strcmp(buf, "pseudo-locked") && mode == RDT_MODE_PSEUDO_LOCKED))
+	/* Do nothing and return success if user asks for current mode */
+	if (user_m == rdtgrp->mode)
 		goto out;
 
-	if (mode == RDT_MODE_PSEUDO_LOCKED) {
+	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
 		rdt_last_cmd_puts("Cannot change pseudo-locked group\n");
 		ret = -EINVAL;
 		goto out;
 	}
 
-	if (!strcmp(buf, "shareable")) {
+	if (user_m == RDT_MODE_SHAREABLE) {
 		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
 			ret = rdtgroup_locksetup_exit(rdtgrp);
 			if (ret)
 				goto out;
 		}
-		rdtgrp->mode = RDT_MODE_SHAREABLE;
-	} else if (!strcmp(buf, "exclusive")) {
+	} else if (user_m == RDT_MODE_EXCLUSIVE) {
 		if (!rdtgroup_mode_test_exclusive(rdtgrp)) {
 			ret = -EINVAL;
 			goto out;
@@ -1462,16 +1464,16 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
 			if (ret)
 				goto out;
 		}
-		rdtgrp->mode = RDT_MODE_EXCLUSIVE;
-	} else if (!strcmp(buf, "pseudo-locksetup")) {
+	} else if (user_m == RDT_MODE_PSEUDO_LOCKSETUP) {
 		ret = rdtgroup_locksetup_enter(rdtgrp);
 		if (ret)
 			goto out;
-		rdtgrp->mode = RDT_MODE_PSEUDO_LOCKSETUP;
-	} else {
+	} else if (user_m == RDT_MODE_PSEUDO_LOCKED) {
 		rdt_last_cmd_puts("Unknown or unsupported mode\n");
 		ret = -EINVAL;
+		goto out;
 	}
+	rdtgrp->mode = user_m;
 
 out:
 	rdtgroup_kn_unlock(of->kn);
-- 
2.21.0

Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Andy Shevchenko]

On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
<reinette.chatre@intel.com> wrote:
>
> The user input to files in the resctrl filesystem are expected to be
> terminated with a newline. Testing the user input includes a test for
> the presence of a newline and then replacing the newline with NUL
> byte followed by comparison using strcmp().
>
> sysfs_streq() exists to test if strings are equal, treating both NUL and
> newline-then-NUL as equivalent string terminations. Even more,
> sysfs_match_string() exists to match a given string in an array using
> sysfs_streq().
>
> Replace existing strcmp() comparisons of strings that are terminated
> with a newline with more appropriate sysfs_streq() via the
> sysfs_match_string() API that can perform the match across the different
> mode strings that are already maintained in an array.

...

> Changes since V4:
> - Remove "mode" local variable from rdtgroup_mode_write(). This variable
>   was previously used to create shorter lines with the original strcmp()
>   code that was removed in patch 4/4.
> - Andy pointed out that the repeated assignment to rdtgrp->mode could be
>   replaced by a single assignment after all the checks. This was initially
>   rejected because it would let the "RDT_MODE_PSEUDO_LOCKED" assignment
>   slip through. Even so, Andy's feedback revealed that the new changes
>   unintentionally let a user's attempt at setting the mode to pseudo-locked
>   be silently ignored where it previously reported an error. Restore original
>   user space behavior by returning success when user attempts to change any
>   mode when it is already the current mode (including pseudo-locked) and
>   returning failure when user attempts to set the mode to pseudo-locked.
>   After this change it is possible to follow Andy's original suggestion
>   of using a single assignment. (Andy)

Glad we can do it!

...

> +       ret = sysfs_match_string(rdt_mode_str, buf);
> +       if (ret < 0) {
> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");

> +               ret = -EINVAL;

This is redundant.

> +               goto out;
> +       }

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Andy Shevchenko]

On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
<reinette.chatre@intel.com> wrote:

...

> +       ret = sysfs_match_string(rdt_mode_str, buf);
> +       if (ret < 0) {
> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +
> +       user_m = ret;

> +       } else if (user_m == RDT_MODE_PSEUDO_LOCKED) {
>                 rdt_last_cmd_puts("Unknown or unsupported mode\n");
>                 ret = -EINVAL;
> +               goto out;
>         }

Can't we unify latter with a former like

  if (ret == RDT_MODE_PSEUDO_LOCKED)
    ret = -EINVAL;
  if (ret < 0) {
      rdt_last_cmd_puts("Unknown or unsupported mode\n");
      goto out;
  }

?

Or closer to initial like

  if (ret < 0 || ret == RDT_MODE_PSEUDO_LOCKED) {
    rdt_last_cmd_puts("Unknown or unsupported mode\n");
    ret = -EINVAL;
    goto out;
  }

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Reinette Chatre]

Hi Andy,

On a high level the changes from v4 to v5 aimed to address your feedback
and also ensure that original user interface behavior is maintained.

On 5/19/2020 1:28 AM, Andy Shevchenko wrote:
> On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
> <reinette.chatre@intel.com> wrote:
> 
> ...
> 
>> +       ret = sysfs_match_string(rdt_mode_str, buf);
>> +       if (ret < 0) {
>> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
>> +               ret = -EINVAL;
>> +               goto out;
>> +       }

From your previous email ...

>> +       ret = sysfs_match_string(rdt_mode_str, buf);
>> +       if (ret < 0) {
>> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
>
>> +               ret = -EINVAL;
>
> This is redundant.

I understand that shadowing an error code is generally of concern. In
this case the error code is set to -EINVAL to ensure that it is the same
error code that was returned to user space originally and will continue
to be so no matter what changes may come to sysfs_match_string().

>> +
>> +       user_m = ret;
> 
>> +       } else if (user_m == RDT_MODE_PSEUDO_LOCKED) {
>>                 rdt_last_cmd_puts("Unknown or unsupported mode\n");
>>                 ret = -EINVAL;
>> +               goto out;
>>         }
> 
> Can't we unify latter with a former like
> 
>   if (ret == RDT_MODE_PSEUDO_LOCKED)
>     ret = -EINVAL;
>   if (ret < 0) {
>       rdt_last_cmd_puts("Unknown or unsupported mode\n");
>       goto out;
>   }
> 
> ?
> 
> Or closer to initial like
> 
>   if (ret < 0 || ret == RDT_MODE_PSEUDO_LOCKED) {
>     rdt_last_cmd_puts("Unknown or unsupported mode\n");
>     ret = -EINVAL;
>     goto out;
>   }
> 

This would have been ideal if done from the start but currently "0" is
returned if the current mode is pseudo-locked and user attempts to
change the mode to pseudo-locked. Thus, to maintain the current user
interface the check if user wants to set pseudo-locked mode is moved
after the check if new mode is same as existing mode and thus not
unified because that will result in an error returned always when user
requests pseudo-locked mode.

Reinette

Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Andy Shevchenko]

On Tue, May 19, 2020 at 08:50:22AM -0700, Reinette Chatre wrote:
> On 5/19/2020 1:28 AM, Andy Shevchenko wrote:
> > On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
> > <reinette.chatre@intel.com> wrote:

...

> >> +       ret = sysfs_match_string(rdt_mode_str, buf);
> >> +       if (ret < 0) {
> >> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
> >> +               ret = -EINVAL;
> >> +               goto out;
> >> +       }
> 
> From your previous email ...
> 
> >> +       ret = sysfs_match_string(rdt_mode_str, buf);
> >> +       if (ret < 0) {
> >> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
> >
> >> +               ret = -EINVAL;
> >
> > This is redundant.
> 
> I understand that shadowing an error code is generally of concern. In
> this case the error code is set to -EINVAL to ensure that it is the same
> error code that was returned to user space originally and will continue
> to be so no matter what changes may come to sysfs_match_string().

It returns -EINVAL and if that will be ever changed this driver would be one of
hundreds who suffers.

...

> > Can't we unify latter with a former like ...

> This would have been ideal if done from the start but currently "0" is
> returned if the current mode is pseudo-locked and user attempts to
> change the mode to pseudo-locked. Thus, to maintain the current user
> interface the check if user wants to set pseudo-locked mode is moved
> after the check if new mode is same as existing mode and thus not
> unified because that will result in an error returned always when user
> requests pseudo-locked mode.

Ah, I see now.

But we can then drop the check from sysfs_match_string() returned value, like

	user_m = sysfs_match_string();
	if (...) {
		...
	} else { // w/o even checking for the PSEUDO_LOCKED
		...
		goto out;
	}

Can we?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Andy Shevchenko]

On Tue, May 19, 2020 at 07:07:10PM +0300, Andy Shevchenko wrote:
> On Tue, May 19, 2020 at 08:50:22AM -0700, Reinette Chatre wrote:
> > On 5/19/2020 1:28 AM, Andy Shevchenko wrote:
> > > On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
> > > <reinette.chatre@intel.com> wrote:

...

> > > Can't we unify latter with a former like ...
> 
> > This would have been ideal if done from the start but currently "0" is
> > returned if the current mode is pseudo-locked and user attempts to
> > change the mode to pseudo-locked. Thus, to maintain the current user
> > interface the check if user wants to set pseudo-locked mode is moved
> > after the check if new mode is same as existing mode and thus not
> > unified because that will result in an error returned always when user
> > requests pseudo-locked mode.
> 
> Ah, I see now.
> 
> But we can then drop the check from sysfs_match_string() returned value, like
> 
> 	user_m = sysfs_match_string();

Yes, here some additional checks like

	if (user_m == mode)
		goto out;

> 	if (...) {
> 		...
> 	} else { // w/o even checking for the PSEUDO_LOCKED
> 		...
> 		goto out;
> 	}
> 
> Can we?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Reinette Chatre]

Hi Andy,

On 5/19/2020 9:07 AM, Andy Shevchenko wrote:
> On Tue, May 19, 2020 at 08:50:22AM -0700, Reinette Chatre wrote:
>> On 5/19/2020 1:28 AM, Andy Shevchenko wrote:
>>> On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
>>> <reinette.chatre@intel.com> wrote:
> 
> ...
> 
>>>> +       ret = sysfs_match_string(rdt_mode_str, buf);
>>>> +       if (ret < 0) {
>>>> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
>>>> +               ret = -EINVAL;
>>>> +               goto out;
>>>> +       }
>>
>> From your previous email ...
>>
>>>> +       ret = sysfs_match_string(rdt_mode_str, buf);
>>>> +       if (ret < 0) {
>>>> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
>>>
>>>> +               ret = -EINVAL;
>>>
>>> This is redundant.
>>
>> I understand that shadowing an error code is generally of concern. In
>> this case the error code is set to -EINVAL to ensure that it is the same
>> error code that was returned to user space originally and will continue
>> to be so no matter what changes may come to sysfs_match_string().
> 
> It returns -EINVAL and if that will be ever changed this driver would be one of
> hundreds who suffers.

Not if we keep this change ... but that is no longer of concern with the
removal of the check as you propose later.

> 
> ...
> 
>>> Can't we unify latter with a former like ...
> 
>> This would have been ideal if done from the start but currently "0" is
>> returned if the current mode is pseudo-locked and user attempts to
>> change the mode to pseudo-locked. Thus, to maintain the current user
>> interface the check if user wants to set pseudo-locked mode is moved
>> after the check if new mode is same as existing mode and thus not
>> unified because that will result in an error returned always when user
>> requests pseudo-locked mode.
> 
> Ah, I see now.
> 
> But we can then drop the check from sysfs_match_string() returned value, like
> 
> 	user_m = sysfs_match_string();
> 	if (...) {
> 		...
> 	} else { // w/o even checking for the PSEUDO_LOCKED
> 		...
> 		goto out;
> 	}
> 
> Can we?
> 

Yes, we can. Will do.

Reinette