[PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

[PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

[Juri Lelli]

Qais reported [1] that iterating over all tasks when rebuilding root
domains for finding out which ones are DEADLINE and need their bandwidth
correctly restored on such root domains can be a costly operation (10+
ms delays on suspend-resume). He proposed we skip rebuilding root
domains for certain operations, but that approach seemed arch specific
and possibly prone to errors, as paths that ultimately trigger a rebuild
might be quite convoluted (thanks Qais for spending time on this!).

This is v2 of an alternative approach (v1 at [3]) to fix the problem.

 01/06 - Rename functions deadline with DEADLINE accounting (cleanup
         suggested by Qais) - no functional change
 02/06 - Bring back cpuset_mutex (so that we have write access to cpusets
         from scheduler operations - and we also fix some problems
         associated to percpu_cpuset_rwsem)
 03/06 - Keep track of the number of DEADLINE tasks belonging to each cpuset
 04/06 - Use this information to only perform the costly iteration if
         DEADLINE tasks are actually present in the cpuset for which a
         corresponding root domain is being rebuilt
 05/06 - Create DL BW alloc, free & check overflow interface for bulk
         bandwidth allocation/removal - no functional change 
 06/06 - Fix bandwidth allocation handling for cgroup operation
         involving multiple tasks

With respect to the v1 posting [3]

 1 - rebase on top of Linus' tree as of today (865fdb08197e)
 2 - move patch 6 to position 4 - Qais

As the rebase needed some work, I decided to remove the tested and
reviewed bys. Please take another look, just in case I messed something
up.

This set is also available from

https://github.com/jlelli/linux.git deadline/rework-cpusets

Best,
Juri

1 - https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
2 - RFC https://lore.kernel.org/lkml/20230315121812.206079-1-juri.lelli@redhat.com/
3 - v1  https://lore.kernel.org/lkml/20230329125558.255239-1-juri.lelli@redhat.com/

Dietmar Eggemann (2):
  sched/deadline: Create DL BW alloc, free & check overflow interface
  cgroup/cpuset: Free DL BW in case can_attach() fails

Juri Lelli (4):
  cgroup/cpuset: Rename functions dealing with DEADLINE accounting
  sched/cpuset: Bring back cpuset_mutex
  sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets
  cgroup/cpuset: Iterate only if DEADLINE tasks are present

 include/linux/cpuset.h  |  12 +-
 include/linux/sched.h   |   4 +-
 kernel/cgroup/cgroup.c  |   4 +
 kernel/cgroup/cpuset.c  | 242 ++++++++++++++++++++++++++--------------
 kernel/sched/core.c     |  41 +++----
 kernel/sched/deadline.c |  67 ++++++++---
 kernel/sched/sched.h    |   2 +-
 7 files changed, 244 insertions(+), 128 deletions(-)

-- 
2.40.1

[PATCH v2 1/6] cgroup/cpuset: Rename functions dealing with DEADLINE accounting

[Juri Lelli]

rebuild_root_domains() and update_tasks_root_domain() have neutral
names, but actually deal with DEADLINE bandwidth accounting.

Rename them to use 'dl_' prefix so that intent is more clear.

No functional change.

Suggested-by: Qais Yousef <qyousef@layalina.io>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 kernel/cgroup/cpuset.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index e4ca2dd2b764..428ab46291e2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1066,7 +1066,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
 	return ndoms;
 }
 
-static void update_tasks_root_domain(struct cpuset *cs)
+static void dl_update_tasks_root_domain(struct cpuset *cs)
 {
 	struct css_task_iter it;
 	struct task_struct *task;
@@ -1079,7 +1079,7 @@ static void update_tasks_root_domain(struct cpuset *cs)
 	css_task_iter_end(&it);
 }
 
-static void rebuild_root_domains(void)
+static void dl_rebuild_rd_accounting(void)
 {
 	struct cpuset *cs = NULL;
 	struct cgroup_subsys_state *pos_css;
@@ -1107,7 +1107,7 @@ static void rebuild_root_domains(void)
 
 		rcu_read_unlock();
 
-		update_tasks_root_domain(cs);
+		dl_update_tasks_root_domain(cs);
 
 		rcu_read_lock();
 		css_put(&cs->css);
@@ -1121,7 +1121,7 @@ partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
 {
 	mutex_lock(&sched_domains_mutex);
 	partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
-	rebuild_root_domains();
+	dl_rebuild_rd_accounting();
 	mutex_unlock(&sched_domains_mutex);
 }
 
-- 
2.40.1

Re: [PATCH v2 1/6] cgroup/cpuset: Rename functions dealing with DEADLINE accounting

[Waiman Long]

On 5/3/23 03:22, Juri Lelli wrote:
> rebuild_root_domains() and update_tasks_root_domain() have neutral
> names, but actually deal with DEADLINE bandwidth accounting.
>
> Rename them to use 'dl_' prefix so that intent is more clear.
>
> No functional change.
>
> Suggested-by: Qais Yousef <qyousef@layalina.io>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
>   kernel/cgroup/cpuset.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index e4ca2dd2b764..428ab46291e2 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1066,7 +1066,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
>   	return ndoms;
>   }
>   
> -static void update_tasks_root_domain(struct cpuset *cs)
> +static void dl_update_tasks_root_domain(struct cpuset *cs)
>   {
>   	struct css_task_iter it;
>   	struct task_struct *task;
> @@ -1079,7 +1079,7 @@ static void update_tasks_root_domain(struct cpuset *cs)
>   	css_task_iter_end(&it);
>   }
>   
> -static void rebuild_root_domains(void)
> +static void dl_rebuild_rd_accounting(void)
>   {
>   	struct cpuset *cs = NULL;
>   	struct cgroup_subsys_state *pos_css;
> @@ -1107,7 +1107,7 @@ static void rebuild_root_domains(void)
>   
>   		rcu_read_unlock();
>   
> -		update_tasks_root_domain(cs);
> +		dl_update_tasks_root_domain(cs);
>   
>   		rcu_read_lock();
>   		css_put(&cs->css);
> @@ -1121,7 +1121,7 @@ partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
>   {
>   	mutex_lock(&sched_domains_mutex);
>   	partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
> -	rebuild_root_domains();
> +	dl_rebuild_rd_accounting();
>   	mutex_unlock(&sched_domains_mutex);
>   }
>   
Reviewed-by: Waiman Long <longman@redhat.com>

[PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex

[Juri Lelli]

Turns out percpu_cpuset_rwsem - commit 1243dc518c9d ("cgroup/cpuset:
Convert cpuset_mutex to percpu_rwsem") - wasn't such a brilliant idea,
as it has been reported to cause slowdowns in workloads that need to
change cpuset configuration frequently and it is also not implementing
priority inheritance (which causes troubles with realtime workloads).

Convert percpu_cpuset_rwsem back to regular cpuset_mutex. Also grab it
only for SCHED_DEADLINE tasks (other policies don't care about stable
cpusets anyway).

Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 include/linux/cpuset.h |   8 +--
 kernel/cgroup/cpuset.c | 157 ++++++++++++++++++++---------------------
 kernel/sched/core.c    |  22 ++++--
 3 files changed, 97 insertions(+), 90 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 980b76a1237e..f90e6325d707 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -71,8 +71,8 @@ extern void cpuset_init_smp(void);
 extern void cpuset_force_rebuild(void);
 extern void cpuset_update_active_cpus(void);
 extern void cpuset_wait_for_hotplug(void);
-extern void cpuset_read_lock(void);
-extern void cpuset_read_unlock(void);
+extern void cpuset_lock(void);
+extern void cpuset_unlock(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
 extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@@ -189,8 +189,8 @@ static inline void cpuset_update_active_cpus(void)
 
 static inline void cpuset_wait_for_hotplug(void) { }
 
-static inline void cpuset_read_lock(void) { }
-static inline void cpuset_read_unlock(void) { }
+static inline void cpuset_lock(void) { }
+static inline void cpuset_unlock(void) { }
 
 static inline void cpuset_cpus_allowed(struct task_struct *p,
 				       struct cpumask *mask)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 428ab46291e2..ee66be215fb9 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -366,22 +366,21 @@ static struct cpuset top_cpuset = {
 		if (is_cpuset_online(((des_cs) = css_cs((pos_css)))))
 
 /*
- * There are two global locks guarding cpuset structures - cpuset_rwsem and
+ * There are two global locks guarding cpuset structures - cpuset_mutex and
  * callback_lock. We also require taking task_lock() when dereferencing a
  * task's cpuset pointer. See "The task_lock() exception", at the end of this
- * comment.  The cpuset code uses only cpuset_rwsem write lock.  Other
- * kernel subsystems can use cpuset_read_lock()/cpuset_read_unlock() to
- * prevent change to cpuset structures.
+ * comment.  The cpuset code uses only cpuset_mutex. Other kernel subsystems
+ * can use cpuset_lock()/cpuset_unlock() to prevent change to cpuset
+ * structures.
  *
  * A task must hold both locks to modify cpusets.  If a task holds
- * cpuset_rwsem, it blocks others wanting that rwsem, ensuring that it
- * is the only task able to also acquire callback_lock and be able to
- * modify cpusets.  It can perform various checks on the cpuset structure
- * first, knowing nothing will change.  It can also allocate memory while
- * just holding cpuset_rwsem.  While it is performing these checks, various
- * callback routines can briefly acquire callback_lock to query cpusets.
- * Once it is ready to make the changes, it takes callback_lock, blocking
- * everyone else.
+ * cpuset_mutex, it blocks others, ensuring that it is the only task able to
+ * also acquire callback_lock and be able to modify cpusets.  It can perform
+ * various checks on the cpuset structure first, knowing nothing will change.
+ * It can also allocate memory while just holding cpuset_mutex.  While it is
+ * performing these checks, various callback routines can briefly acquire
+ * callback_lock to query cpusets.  Once it is ready to make the changes, it
+ * takes callback_lock, blocking everyone else.
  *
  * Calls to the kernel memory allocator can not be made while holding
  * callback_lock, as that would risk double tripping on callback_lock
@@ -403,16 +402,16 @@ static struct cpuset top_cpuset = {
  * guidelines for accessing subsystem state in kernel/cgroup.c
  */
 
-DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
+static DEFINE_MUTEX(cpuset_mutex);
 
-void cpuset_read_lock(void)
+void cpuset_lock(void)
 {
-	percpu_down_read(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 }
 
-void cpuset_read_unlock(void)
+void cpuset_unlock(void)
 {
-	percpu_up_read(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 }
 
 static DEFINE_SPINLOCK(callback_lock);
@@ -496,7 +495,7 @@ static inline bool partition_is_populated(struct cpuset *cs,
  * One way or another, we guarantee to return some non-empty subset
  * of cpu_online_mask.
  *
- * Call with callback_lock or cpuset_rwsem held.
+ * Call with callback_lock or cpuset_mutex held.
  */
 static void guarantee_online_cpus(struct task_struct *tsk,
 				  struct cpumask *pmask)
@@ -538,7 +537,7 @@ static void guarantee_online_cpus(struct task_struct *tsk,
  * One way or another, we guarantee to return some non-empty subset
  * of node_states[N_MEMORY].
  *
- * Call with callback_lock or cpuset_rwsem held.
+ * Call with callback_lock or cpuset_mutex held.
  */
 static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
 {
@@ -550,7 +549,7 @@ static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
 /*
  * update task's spread flag if cpuset's page/slab spread flag is set
  *
- * Call with callback_lock or cpuset_rwsem held. The check can be skipped
+ * Call with callback_lock or cpuset_mutex held. The check can be skipped
  * if on default hierarchy.
  */
 static void cpuset_update_task_spread_flags(struct cpuset *cs,
@@ -575,7 +574,7 @@ static void cpuset_update_task_spread_flags(struct cpuset *cs,
  *
  * One cpuset is a subset of another if all its allowed CPUs and
  * Memory Nodes are a subset of the other, and its exclusive flags
- * are only set if the other's are set.  Call holding cpuset_rwsem.
+ * are only set if the other's are set.  Call holding cpuset_mutex.
  */
 
 static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
@@ -713,7 +712,7 @@ static int validate_change_legacy(struct cpuset *cur, struct cpuset *trial)
  * If we replaced the flag and mask values of the current cpuset
  * (cur) with those values in the trial cpuset (trial), would
  * our various subset and exclusive rules still be valid?  Presumes
- * cpuset_rwsem held.
+ * cpuset_mutex held.
  *
  * 'cur' is the address of an actual, in-use cpuset.  Operations
  * such as list traversal that depend on the actual address of the
@@ -829,7 +828,7 @@ static void update_domain_attr_tree(struct sched_domain_attr *dattr,
 	rcu_read_unlock();
 }
 
-/* Must be called with cpuset_rwsem held.  */
+/* Must be called with cpuset_mutex held.  */
 static inline int nr_cpusets(void)
 {
 	/* jump label reference count + the top-level cpuset */
@@ -855,7 +854,7 @@ static inline int nr_cpusets(void)
  * domains when operating in the severe memory shortage situations
  * that could cause allocation failures below.
  *
- * Must be called with cpuset_rwsem held.
+ * Must be called with cpuset_mutex held.
  *
  * The three key local variables below are:
  *    cp - cpuset pointer, used (together with pos_css) to perform a
@@ -1084,7 +1083,7 @@ static void dl_rebuild_rd_accounting(void)
 	struct cpuset *cs = NULL;
 	struct cgroup_subsys_state *pos_css;
 
-	percpu_rwsem_assert_held(&cpuset_rwsem);
+	lockdep_assert_held(&cpuset_mutex);
 	lockdep_assert_cpus_held();
 	lockdep_assert_held(&sched_domains_mutex);
 
@@ -1134,7 +1133,7 @@ partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
  * 'cpus' is removed, then call this routine to rebuild the
  * scheduler's dynamic sched domains.
  *
- * Call with cpuset_rwsem held.  Takes cpus_read_lock().
+ * Call with cpuset_mutex held.  Takes cpus_read_lock().
  */
 static void rebuild_sched_domains_locked(void)
 {
@@ -1145,7 +1144,7 @@ static void rebuild_sched_domains_locked(void)
 	int ndoms;
 
 	lockdep_assert_cpus_held();
-	percpu_rwsem_assert_held(&cpuset_rwsem);
+	lockdep_assert_held(&cpuset_mutex);
 
 	/*
 	 * If we have raced with CPU hotplug, return early to avoid
@@ -1196,9 +1195,9 @@ static void rebuild_sched_domains_locked(void)
 void rebuild_sched_domains(void)
 {
 	cpus_read_lock();
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	rebuild_sched_domains_locked();
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
 }
 
@@ -1208,7 +1207,7 @@ void rebuild_sched_domains(void)
  * @new_cpus: the temp variable for the new effective_cpus mask
  *
  * Iterate through each task of @cs updating its cpus_allowed to the
- * effective cpuset's.  As this function is called with cpuset_rwsem held,
+ * effective cpuset's.  As this function is called with cpuset_mutex held,
  * cpuset membership stays stable. For top_cpuset, task_cpu_possible_mask()
  * is used instead of effective_cpus to make sure all offline CPUs are also
  * included as hotplug code won't update cpumasks for tasks in top_cpuset.
@@ -1322,7 +1321,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
 	int old_prs, new_prs;
 	int part_error = PERR_NONE;	/* Partition error? */
 
-	percpu_rwsem_assert_held(&cpuset_rwsem);
+	lockdep_assert_held(&cpuset_mutex);
 
 	/*
 	 * The parent must be a partition root.
@@ -1545,7 +1544,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
  *
  * On legacy hierarchy, effective_cpus will be the same with cpu_allowed.
  *
- * Called with cpuset_rwsem held
+ * Called with cpuset_mutex held
  */
 static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 				 bool force)
@@ -1705,7 +1704,7 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
 	struct cpuset *sibling;
 	struct cgroup_subsys_state *pos_css;
 
-	percpu_rwsem_assert_held(&cpuset_rwsem);
+	lockdep_assert_held(&cpuset_mutex);
 
 	/*
 	 * Check all its siblings and call update_cpumasks_hier()
@@ -1955,12 +1954,12 @@ static void *cpuset_being_rebound;
  * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
  *
  * Iterate through each task of @cs updating its mems_allowed to the
- * effective cpuset's.  As this function is called with cpuset_rwsem held,
+ * effective cpuset's.  As this function is called with cpuset_mutex held,
  * cpuset membership stays stable.
  */
 static void update_tasks_nodemask(struct cpuset *cs)
 {
-	static nodemask_t newmems;	/* protected by cpuset_rwsem */
+	static nodemask_t newmems;	/* protected by cpuset_mutex */
 	struct css_task_iter it;
 	struct task_struct *task;
 
@@ -1973,7 +1972,7 @@ static void update_tasks_nodemask(struct cpuset *cs)
 	 * take while holding tasklist_lock.  Forks can happen - the
 	 * mpol_dup() cpuset_being_rebound check will catch such forks,
 	 * and rebind their vma mempolicies too.  Because we still hold
-	 * the global cpuset_rwsem, we know that no other rebind effort
+	 * the global cpuset_mutex, we know that no other rebind effort
 	 * will be contending for the global variable cpuset_being_rebound.
 	 * It's ok if we rebind the same mm twice; mpol_rebind_mm()
 	 * is idempotent.  Also migrate pages in each mm to new nodes.
@@ -2019,7 +2018,7 @@ static void update_tasks_nodemask(struct cpuset *cs)
  *
  * On legacy hierarchy, effective_mems will be the same with mems_allowed.
  *
- * Called with cpuset_rwsem held
+ * Called with cpuset_mutex held
  */
 static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
 {
@@ -2072,7 +2071,7 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
  * mempolicies and if the cpuset is marked 'memory_migrate',
  * migrate the tasks pages to the new memory.
  *
- * Call with cpuset_rwsem held. May take callback_lock during call.
+ * Call with cpuset_mutex held. May take callback_lock during call.
  * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
  * lock each such tasks mm->mmap_lock, scan its vma's and rebind
  * their mempolicies to the cpusets new mems_allowed.
@@ -2164,7 +2163,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val)
  * @cs: the cpuset in which each task's spread flags needs to be changed
  *
  * Iterate through each task of @cs updating its spread flags.  As this
- * function is called with cpuset_rwsem held, cpuset membership stays
+ * function is called with cpuset_mutex held, cpuset membership stays
  * stable.
  */
 static void update_tasks_flags(struct cpuset *cs)
@@ -2184,7 +2183,7 @@ static void update_tasks_flags(struct cpuset *cs)
  * cs:		the cpuset to update
  * turning_on: 	whether the flag is being set or cleared
  *
- * Call with cpuset_rwsem held.
+ * Call with cpuset_mutex held.
  */
 
 static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
@@ -2234,7 +2233,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
  * @new_prs: new partition root state
  * Return: 0 if successful, != 0 if error
  *
- * Call with cpuset_rwsem held.
+ * Call with cpuset_mutex held.
  */
 static int update_prstate(struct cpuset *cs, int new_prs)
 {
@@ -2472,7 +2471,7 @@ static int cpuset_can_attach_check(struct cpuset *cs)
 	return 0;
 }
 
-/* Called by cgroups to determine if a cpuset is usable; cpuset_rwsem held */
+/* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
 static int cpuset_can_attach(struct cgroup_taskset *tset)
 {
 	struct cgroup_subsys_state *css;
@@ -2484,7 +2483,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
 	cs = css_cs(css);
 
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 
 	/* Check to see if task is allowed in the cpuset */
 	ret = cpuset_can_attach_check(cs);
@@ -2506,7 +2505,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 	 */
 	cs->attach_in_progress++;
 out_unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	return ret;
 }
 
@@ -2518,15 +2517,15 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 	cgroup_taskset_first(tset, &css);
 	cs = css_cs(css);
 
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	cs->attach_in_progress--;
 	if (!cs->attach_in_progress)
 		wake_up(&cpuset_attach_wq);
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 }
 
 /*
- * Protected by cpuset_rwsem. cpus_attach is used only by cpuset_attach_task()
+ * Protected by cpuset_mutex. cpus_attach is used only by cpuset_attach_task()
  * but we can't allocate it dynamically there.  Define it global and
  * allocate from cpuset_init().
  */
@@ -2535,7 +2534,7 @@ static nodemask_t cpuset_attach_nodemask_to;
 
 static void cpuset_attach_task(struct cpuset *cs, struct task_struct *task)
 {
-	percpu_rwsem_assert_held(&cpuset_rwsem);
+	lockdep_assert_held(&cpuset_mutex);
 
 	if (cs != &top_cpuset)
 		guarantee_online_cpus(task, cpus_attach);
@@ -2565,7 +2564,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	cs = css_cs(css);
 
 	lockdep_assert_cpus_held();	/* see cgroup_attach_lock() */
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	cpus_updated = !cpumask_equal(cs->effective_cpus,
 				      oldcs->effective_cpus);
 	mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
@@ -2626,7 +2625,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	if (!cs->attach_in_progress)
 		wake_up(&cpuset_attach_wq);
 
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 }
 
 /* The various types of files and directories in a cpuset file system */
@@ -2658,7 +2657,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
 	int retval = 0;
 
 	cpus_read_lock();
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs)) {
 		retval = -ENODEV;
 		goto out_unlock;
@@ -2694,7 +2693,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
 		break;
 	}
 out_unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
 	return retval;
 }
@@ -2707,7 +2706,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
 	int retval = -ENODEV;
 
 	cpus_read_lock();
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs))
 		goto out_unlock;
 
@@ -2720,7 +2719,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
 		break;
 	}
 out_unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
 	return retval;
 }
@@ -2753,7 +2752,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 	 * operation like this one can lead to a deadlock through kernfs
 	 * active_ref protection.  Let's break the protection.  Losing the
 	 * protection is okay as we check whether @cs is online after
-	 * grabbing cpuset_rwsem anyway.  This only happens on the legacy
+	 * grabbing cpuset_mutex anyway.  This only happens on the legacy
 	 * hierarchies.
 	 */
 	css_get(&cs->css);
@@ -2761,7 +2760,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 	flush_work(&cpuset_hotplug_work);
 
 	cpus_read_lock();
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs))
 		goto out_unlock;
 
@@ -2785,7 +2784,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 
 	free_cpuset(trialcs);
 out_unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
 	kernfs_unbreak_active_protection(of->kn);
 	css_put(&cs->css);
@@ -2933,13 +2932,13 @@ static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf,
 
 	css_get(&cs->css);
 	cpus_read_lock();
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs))
 		goto out_unlock;
 
 	retval = update_prstate(cs, val);
 out_unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
 	css_put(&cs->css);
 	return retval ?: nbytes;
@@ -3156,7 +3155,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 		return 0;
 
 	cpus_read_lock();
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 
 	set_bit(CS_ONLINE, &cs->flags);
 	if (is_spread_page(parent))
@@ -3207,7 +3206,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 	cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
 	spin_unlock_irq(&callback_lock);
 out_unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
 	return 0;
 }
@@ -3228,7 +3227,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
 	struct cpuset *cs = css_cs(css);
 
 	cpus_read_lock();
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 
 	if (is_partition_valid(cs))
 		update_prstate(cs, 0);
@@ -3247,7 +3246,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
 	cpuset_dec();
 	clear_bit(CS_ONLINE, &cs->flags);
 
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
 }
 
@@ -3260,7 +3259,7 @@ static void cpuset_css_free(struct cgroup_subsys_state *css)
 
 static void cpuset_bind(struct cgroup_subsys_state *root_css)
 {
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	spin_lock_irq(&callback_lock);
 
 	if (is_in_v2_mode()) {
@@ -3273,7 +3272,7 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)
 	}
 
 	spin_unlock_irq(&callback_lock);
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 }
 
 /*
@@ -3294,7 +3293,7 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
 		return 0;
 
 	lockdep_assert_held(&cgroup_mutex);
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 
 	/* Check to see if task is allowed in the cpuset */
 	ret = cpuset_can_attach_check(cs);
@@ -3315,7 +3314,7 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
 	 */
 	cs->attach_in_progress++;
 out_unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 	return ret;
 }
 
@@ -3331,11 +3330,11 @@ static void cpuset_cancel_fork(struct task_struct *task, struct css_set *cset)
 	if (same_cs)
 		return;
 
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	cs->attach_in_progress--;
 	if (!cs->attach_in_progress)
 		wake_up(&cpuset_attach_wq);
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 }
 
 /*
@@ -3363,7 +3362,7 @@ static void cpuset_fork(struct task_struct *task)
 	}
 
 	/* CLONE_INTO_CGROUP */
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
 	cpuset_attach_task(cs, task);
 
@@ -3371,7 +3370,7 @@ static void cpuset_fork(struct task_struct *task)
 	if (!cs->attach_in_progress)
 		wake_up(&cpuset_attach_wq);
 
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 }
 
 struct cgroup_subsys cpuset_cgrp_subsys = {
@@ -3472,7 +3471,7 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
 	is_empty = cpumask_empty(cs->cpus_allowed) ||
 		   nodes_empty(cs->mems_allowed);
 
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 
 	/*
 	 * Move tasks to the nearest ancestor with execution resources,
@@ -3482,7 +3481,7 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
 	if (is_empty)
 		remove_tasks_in_empty_cpuset(cs);
 
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 }
 
 static void
@@ -3533,14 +3532,14 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
 retry:
 	wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
 
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 
 	/*
 	 * We have raced with task attaching. We wait until attaching
 	 * is finished, so we won't attach a task to an empty cpuset.
 	 */
 	if (cs->attach_in_progress) {
-		percpu_up_write(&cpuset_rwsem);
+		mutex_unlock(&cpuset_mutex);
 		goto retry;
 	}
 
@@ -3637,7 +3636,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
 					    cpus_updated, mems_updated);
 
 unlock:
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 }
 
 /**
@@ -3667,7 +3666,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 	if (on_dfl && !alloc_cpumasks(NULL, &tmp))
 		ptmp = &tmp;
 
-	percpu_down_write(&cpuset_rwsem);
+	mutex_lock(&cpuset_mutex);
 
 	/* fetch the available cpus/mems and find out which changed how */
 	cpumask_copy(&new_cpus, cpu_active_mask);
@@ -3724,7 +3723,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 		update_tasks_nodemask(&top_cpuset);
 	}
 
-	percpu_up_write(&cpuset_rwsem);
+	mutex_unlock(&cpuset_mutex);
 
 	/* if cpus or mems changed, we need to propagate to descendants */
 	if (cpus_updated || mems_updated) {
@@ -4155,7 +4154,7 @@ void __cpuset_memory_pressure_bump(void)
  *  - Used for /proc/<pid>/cpuset.
  *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
  *    doesn't really matter if tsk->cpuset changes after we read it,
- *    and we take cpuset_rwsem, keeping cpuset_attach() from changing it
+ *    and we take cpuset_mutex, keeping cpuset_attach() from changing it
  *    anyway.
  */
 int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 944c3ae39861..d826bec1c522 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7590,6 +7590,7 @@ static int __sched_setscheduler(struct task_struct *p,
 	int reset_on_fork;
 	int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
 	struct rq *rq;
+	bool cpuset_locked = false;
 
 	/* The pi code expects interrupts enabled */
 	BUG_ON(pi && in_interrupt());
@@ -7639,8 +7640,14 @@ static int __sched_setscheduler(struct task_struct *p,
 			return retval;
 	}
 
-	if (pi)
-		cpuset_read_lock();
+	/*
+	 * SCHED_DEADLINE bandwidth accounting relies on stable cpusets
+	 * information.
+	 */
+	if (dl_policy(policy) || dl_policy(p->policy)) {
+		cpuset_locked = true;
+		cpuset_lock();
+	}
 
 	/*
 	 * Make sure no PI-waiters arrive (or leave) while we are
@@ -7716,8 +7723,8 @@ static int __sched_setscheduler(struct task_struct *p,
 	if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
 		policy = oldpolicy = -1;
 		task_rq_unlock(rq, p, &rf);
-		if (pi)
-			cpuset_read_unlock();
+		if (cpuset_locked)
+			cpuset_unlock();
 		goto recheck;
 	}
 
@@ -7784,7 +7791,8 @@ static int __sched_setscheduler(struct task_struct *p,
 	task_rq_unlock(rq, p, &rf);
 
 	if (pi) {
-		cpuset_read_unlock();
+		if (cpuset_locked)
+			cpuset_unlock();
 		rt_mutex_adjust_pi(p);
 	}
 
@@ -7796,8 +7804,8 @@ static int __sched_setscheduler(struct task_struct *p,
 
 unlock:
 	task_rq_unlock(rq, p, &rf);
-	if (pi)
-		cpuset_read_unlock();
+	if (cpuset_locked)
+		cpuset_unlock();
 	return retval;
 }
 
-- 
2.40.1

Re: [PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex

[Waiman Long]

On 5/3/23 03:22, Juri Lelli wrote:
> Turns out percpu_cpuset_rwsem - commit 1243dc518c9d ("cgroup/cpuset:
> Convert cpuset_mutex to percpu_rwsem") - wasn't such a brilliant idea,
> as it has been reported to cause slowdowns in workloads that need to
> change cpuset configuration frequently and it is also not implementing
> priority inheritance (which causes troubles with realtime workloads).
>
> Convert percpu_cpuset_rwsem back to regular cpuset_mutex. Also grab it
> only for SCHED_DEADLINE tasks (other policies don't care about stable
> cpusets anyway).
>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
>   include/linux/cpuset.h |   8 +--
>   kernel/cgroup/cpuset.c | 157 ++++++++++++++++++++---------------------
>   kernel/sched/core.c    |  22 ++++--
>   3 files changed, 97 insertions(+), 90 deletions(-)
>
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 980b76a1237e..f90e6325d707 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -71,8 +71,8 @@ extern void cpuset_init_smp(void);
>   extern void cpuset_force_rebuild(void);
>   extern void cpuset_update_active_cpus(void);
>   extern void cpuset_wait_for_hotplug(void);
> -extern void cpuset_read_lock(void);
> -extern void cpuset_read_unlock(void);
> +extern void cpuset_lock(void);
> +extern void cpuset_unlock(void);
>   extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
>   extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
>   extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
> @@ -189,8 +189,8 @@ static inline void cpuset_update_active_cpus(void)
>   
>   static inline void cpuset_wait_for_hotplug(void) { }
>   
> -static inline void cpuset_read_lock(void) { }
> -static inline void cpuset_read_unlock(void) { }
> +static inline void cpuset_lock(void) { }
> +static inline void cpuset_unlock(void) { }
>   
>   static inline void cpuset_cpus_allowed(struct task_struct *p,
>   				       struct cpumask *mask)
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 428ab46291e2..ee66be215fb9 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -366,22 +366,21 @@ static struct cpuset top_cpuset = {
>   		if (is_cpuset_online(((des_cs) = css_cs((pos_css)))))
>   
>   /*
> - * There are two global locks guarding cpuset structures - cpuset_rwsem and
> + * There are two global locks guarding cpuset structures - cpuset_mutex and
>    * callback_lock. We also require taking task_lock() when dereferencing a
>    * task's cpuset pointer. See "The task_lock() exception", at the end of this
> - * comment.  The cpuset code uses only cpuset_rwsem write lock.  Other
> - * kernel subsystems can use cpuset_read_lock()/cpuset_read_unlock() to
> - * prevent change to cpuset structures.
> + * comment.  The cpuset code uses only cpuset_mutex. Other kernel subsystems
> + * can use cpuset_lock()/cpuset_unlock() to prevent change to cpuset
> + * structures.
>    *
>    * A task must hold both locks to modify cpusets.  If a task holds
> - * cpuset_rwsem, it blocks others wanting that rwsem, ensuring that it
> - * is the only task able to also acquire callback_lock and be able to
> - * modify cpusets.  It can perform various checks on the cpuset structure
> - * first, knowing nothing will change.  It can also allocate memory while
> - * just holding cpuset_rwsem.  While it is performing these checks, various
> - * callback routines can briefly acquire callback_lock to query cpusets.
> - * Once it is ready to make the changes, it takes callback_lock, blocking
> - * everyone else.
> + * cpuset_mutex, it blocks others, ensuring that it is the only task able to
> + * also acquire callback_lock and be able to modify cpusets.  It can perform
> + * various checks on the cpuset structure first, knowing nothing will change.
> + * It can also allocate memory while just holding cpuset_mutex.  While it is
> + * performing these checks, various callback routines can briefly acquire
> + * callback_lock to query cpusets.  Once it is ready to make the changes, it
> + * takes callback_lock, blocking everyone else.
>    *
>    * Calls to the kernel memory allocator can not be made while holding
>    * callback_lock, as that would risk double tripping on callback_lock
> @@ -403,16 +402,16 @@ static struct cpuset top_cpuset = {
>    * guidelines for accessing subsystem state in kernel/cgroup.c
>    */
>   
> -DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
> +static DEFINE_MUTEX(cpuset_mutex);
>   
> -void cpuset_read_lock(void)
> +void cpuset_lock(void)
>   {
> -	percpu_down_read(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   }
>   
> -void cpuset_read_unlock(void)
> +void cpuset_unlock(void)
>   {
> -	percpu_up_read(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   }
>   
>   static DEFINE_SPINLOCK(callback_lock);
> @@ -496,7 +495,7 @@ static inline bool partition_is_populated(struct cpuset *cs,
>    * One way or another, we guarantee to return some non-empty subset
>    * of cpu_online_mask.
>    *
> - * Call with callback_lock or cpuset_rwsem held.
> + * Call with callback_lock or cpuset_mutex held.
>    */
>   static void guarantee_online_cpus(struct task_struct *tsk,
>   				  struct cpumask *pmask)
> @@ -538,7 +537,7 @@ static void guarantee_online_cpus(struct task_struct *tsk,
>    * One way or another, we guarantee to return some non-empty subset
>    * of node_states[N_MEMORY].
>    *
> - * Call with callback_lock or cpuset_rwsem held.
> + * Call with callback_lock or cpuset_mutex held.
>    */
>   static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
>   {
> @@ -550,7 +549,7 @@ static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
>   /*
>    * update task's spread flag if cpuset's page/slab spread flag is set
>    *
> - * Call with callback_lock or cpuset_rwsem held. The check can be skipped
> + * Call with callback_lock or cpuset_mutex held. The check can be skipped
>    * if on default hierarchy.
>    */
>   static void cpuset_update_task_spread_flags(struct cpuset *cs,
> @@ -575,7 +574,7 @@ static void cpuset_update_task_spread_flags(struct cpuset *cs,
>    *
>    * One cpuset is a subset of another if all its allowed CPUs and
>    * Memory Nodes are a subset of the other, and its exclusive flags
> - * are only set if the other's are set.  Call holding cpuset_rwsem.
> + * are only set if the other's are set.  Call holding cpuset_mutex.
>    */
>   
>   static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
> @@ -713,7 +712,7 @@ static int validate_change_legacy(struct cpuset *cur, struct cpuset *trial)
>    * If we replaced the flag and mask values of the current cpuset
>    * (cur) with those values in the trial cpuset (trial), would
>    * our various subset and exclusive rules still be valid?  Presumes
> - * cpuset_rwsem held.
> + * cpuset_mutex held.
>    *
>    * 'cur' is the address of an actual, in-use cpuset.  Operations
>    * such as list traversal that depend on the actual address of the
> @@ -829,7 +828,7 @@ static void update_domain_attr_tree(struct sched_domain_attr *dattr,
>   	rcu_read_unlock();
>   }
>   
> -/* Must be called with cpuset_rwsem held.  */
> +/* Must be called with cpuset_mutex held.  */
>   static inline int nr_cpusets(void)
>   {
>   	/* jump label reference count + the top-level cpuset */
> @@ -855,7 +854,7 @@ static inline int nr_cpusets(void)
>    * domains when operating in the severe memory shortage situations
>    * that could cause allocation failures below.
>    *
> - * Must be called with cpuset_rwsem held.
> + * Must be called with cpuset_mutex held.
>    *
>    * The three key local variables below are:
>    *    cp - cpuset pointer, used (together with pos_css) to perform a
> @@ -1084,7 +1083,7 @@ static void dl_rebuild_rd_accounting(void)
>   	struct cpuset *cs = NULL;
>   	struct cgroup_subsys_state *pos_css;
>   
> -	percpu_rwsem_assert_held(&cpuset_rwsem);
> +	lockdep_assert_held(&cpuset_mutex);
>   	lockdep_assert_cpus_held();
>   	lockdep_assert_held(&sched_domains_mutex);
>   
> @@ -1134,7 +1133,7 @@ partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
>    * 'cpus' is removed, then call this routine to rebuild the
>    * scheduler's dynamic sched domains.
>    *
> - * Call with cpuset_rwsem held.  Takes cpus_read_lock().
> + * Call with cpuset_mutex held.  Takes cpus_read_lock().
>    */
>   static void rebuild_sched_domains_locked(void)
>   {
> @@ -1145,7 +1144,7 @@ static void rebuild_sched_domains_locked(void)
>   	int ndoms;
>   
>   	lockdep_assert_cpus_held();
> -	percpu_rwsem_assert_held(&cpuset_rwsem);
> +	lockdep_assert_held(&cpuset_mutex);
>   
>   	/*
>   	 * If we have raced with CPU hotplug, return early to avoid
> @@ -1196,9 +1195,9 @@ static void rebuild_sched_domains_locked(void)
>   void rebuild_sched_domains(void)
>   {
>   	cpus_read_lock();
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	rebuild_sched_domains_locked();
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
>   }
>   
> @@ -1208,7 +1207,7 @@ void rebuild_sched_domains(void)
>    * @new_cpus: the temp variable for the new effective_cpus mask
>    *
>    * Iterate through each task of @cs updating its cpus_allowed to the
> - * effective cpuset's.  As this function is called with cpuset_rwsem held,
> + * effective cpuset's.  As this function is called with cpuset_mutex held,
>    * cpuset membership stays stable. For top_cpuset, task_cpu_possible_mask()
>    * is used instead of effective_cpus to make sure all offline CPUs are also
>    * included as hotplug code won't update cpumasks for tasks in top_cpuset.
> @@ -1322,7 +1321,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
>   	int old_prs, new_prs;
>   	int part_error = PERR_NONE;	/* Partition error? */
>   
> -	percpu_rwsem_assert_held(&cpuset_rwsem);
> +	lockdep_assert_held(&cpuset_mutex);
>   
>   	/*
>   	 * The parent must be a partition root.
> @@ -1545,7 +1544,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
>    *
>    * On legacy hierarchy, effective_cpus will be the same with cpu_allowed.
>    *
> - * Called with cpuset_rwsem held
> + * Called with cpuset_mutex held
>    */
>   static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>   				 bool force)
> @@ -1705,7 +1704,7 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
>   	struct cpuset *sibling;
>   	struct cgroup_subsys_state *pos_css;
>   
> -	percpu_rwsem_assert_held(&cpuset_rwsem);
> +	lockdep_assert_held(&cpuset_mutex);
>   
>   	/*
>   	 * Check all its siblings and call update_cpumasks_hier()
> @@ -1955,12 +1954,12 @@ static void *cpuset_being_rebound;
>    * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
>    *
>    * Iterate through each task of @cs updating its mems_allowed to the
> - * effective cpuset's.  As this function is called with cpuset_rwsem held,
> + * effective cpuset's.  As this function is called with cpuset_mutex held,
>    * cpuset membership stays stable.
>    */
>   static void update_tasks_nodemask(struct cpuset *cs)
>   {
> -	static nodemask_t newmems;	/* protected by cpuset_rwsem */
> +	static nodemask_t newmems;	/* protected by cpuset_mutex */
>   	struct css_task_iter it;
>   	struct task_struct *task;
>   
> @@ -1973,7 +1972,7 @@ static void update_tasks_nodemask(struct cpuset *cs)
>   	 * take while holding tasklist_lock.  Forks can happen - the
>   	 * mpol_dup() cpuset_being_rebound check will catch such forks,
>   	 * and rebind their vma mempolicies too.  Because we still hold
> -	 * the global cpuset_rwsem, we know that no other rebind effort
> +	 * the global cpuset_mutex, we know that no other rebind effort
>   	 * will be contending for the global variable cpuset_being_rebound.
>   	 * It's ok if we rebind the same mm twice; mpol_rebind_mm()
>   	 * is idempotent.  Also migrate pages in each mm to new nodes.
> @@ -2019,7 +2018,7 @@ static void update_tasks_nodemask(struct cpuset *cs)
>    *
>    * On legacy hierarchy, effective_mems will be the same with mems_allowed.
>    *
> - * Called with cpuset_rwsem held
> + * Called with cpuset_mutex held
>    */
>   static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
>   {
> @@ -2072,7 +2071,7 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
>    * mempolicies and if the cpuset is marked 'memory_migrate',
>    * migrate the tasks pages to the new memory.
>    *
> - * Call with cpuset_rwsem held. May take callback_lock during call.
> + * Call with cpuset_mutex held. May take callback_lock during call.
>    * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
>    * lock each such tasks mm->mmap_lock, scan its vma's and rebind
>    * their mempolicies to the cpusets new mems_allowed.
> @@ -2164,7 +2163,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val)
>    * @cs: the cpuset in which each task's spread flags needs to be changed
>    *
>    * Iterate through each task of @cs updating its spread flags.  As this
> - * function is called with cpuset_rwsem held, cpuset membership stays
> + * function is called with cpuset_mutex held, cpuset membership stays
>    * stable.
>    */
>   static void update_tasks_flags(struct cpuset *cs)
> @@ -2184,7 +2183,7 @@ static void update_tasks_flags(struct cpuset *cs)
>    * cs:		the cpuset to update
>    * turning_on: 	whether the flag is being set or cleared
>    *
> - * Call with cpuset_rwsem held.
> + * Call with cpuset_mutex held.
>    */
>   
>   static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
> @@ -2234,7 +2233,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
>    * @new_prs: new partition root state
>    * Return: 0 if successful, != 0 if error
>    *
> - * Call with cpuset_rwsem held.
> + * Call with cpuset_mutex held.
>    */
>   static int update_prstate(struct cpuset *cs, int new_prs)
>   {
> @@ -2472,7 +2471,7 @@ static int cpuset_can_attach_check(struct cpuset *cs)
>   	return 0;
>   }
>   
> -/* Called by cgroups to determine if a cpuset is usable; cpuset_rwsem held */
> +/* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
>   static int cpuset_can_attach(struct cgroup_taskset *tset)
>   {
>   	struct cgroup_subsys_state *css;
> @@ -2484,7 +2483,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>   	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
>   	cs = css_cs(css);
>   
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   
>   	/* Check to see if task is allowed in the cpuset */
>   	ret = cpuset_can_attach_check(cs);
> @@ -2506,7 +2505,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>   	 */
>   	cs->attach_in_progress++;
>   out_unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	return ret;
>   }
>   
> @@ -2518,15 +2517,15 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
>   	cgroup_taskset_first(tset, &css);
>   	cs = css_cs(css);
>   
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	cs->attach_in_progress--;
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   }
>   
>   /*
> - * Protected by cpuset_rwsem. cpus_attach is used only by cpuset_attach_task()
> + * Protected by cpuset_mutex. cpus_attach is used only by cpuset_attach_task()
>    * but we can't allocate it dynamically there.  Define it global and
>    * allocate from cpuset_init().
>    */
> @@ -2535,7 +2534,7 @@ static nodemask_t cpuset_attach_nodemask_to;
>   
>   static void cpuset_attach_task(struct cpuset *cs, struct task_struct *task)
>   {
> -	percpu_rwsem_assert_held(&cpuset_rwsem);
> +	lockdep_assert_held(&cpuset_mutex);
>   
>   	if (cs != &top_cpuset)
>   		guarantee_online_cpus(task, cpus_attach);
> @@ -2565,7 +2564,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>   	cs = css_cs(css);
>   
>   	lockdep_assert_cpus_held();	/* see cgroup_attach_lock() */
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	cpus_updated = !cpumask_equal(cs->effective_cpus,
>   				      oldcs->effective_cpus);
>   	mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
> @@ -2626,7 +2625,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
>   
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   }
>   
>   /* The various types of files and directories in a cpuset file system */
> @@ -2658,7 +2657,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
>   	int retval = 0;
>   
>   	cpus_read_lock();
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	if (!is_cpuset_online(cs)) {
>   		retval = -ENODEV;
>   		goto out_unlock;
> @@ -2694,7 +2693,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
>   		break;
>   	}
>   out_unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
>   	return retval;
>   }
> @@ -2707,7 +2706,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
>   	int retval = -ENODEV;
>   
>   	cpus_read_lock();
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	if (!is_cpuset_online(cs))
>   		goto out_unlock;
>   
> @@ -2720,7 +2719,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
>   		break;
>   	}
>   out_unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
>   	return retval;
>   }
> @@ -2753,7 +2752,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
>   	 * operation like this one can lead to a deadlock through kernfs
>   	 * active_ref protection.  Let's break the protection.  Losing the
>   	 * protection is okay as we check whether @cs is online after
> -	 * grabbing cpuset_rwsem anyway.  This only happens on the legacy
> +	 * grabbing cpuset_mutex anyway.  This only happens on the legacy
>   	 * hierarchies.
>   	 */
>   	css_get(&cs->css);
> @@ -2761,7 +2760,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
>   	flush_work(&cpuset_hotplug_work);
>   
>   	cpus_read_lock();
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	if (!is_cpuset_online(cs))
>   		goto out_unlock;
>   
> @@ -2785,7 +2784,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
>   
>   	free_cpuset(trialcs);
>   out_unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
>   	kernfs_unbreak_active_protection(of->kn);
>   	css_put(&cs->css);
> @@ -2933,13 +2932,13 @@ static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf,
>   
>   	css_get(&cs->css);
>   	cpus_read_lock();
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	if (!is_cpuset_online(cs))
>   		goto out_unlock;
>   
>   	retval = update_prstate(cs, val);
>   out_unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
>   	css_put(&cs->css);
>   	return retval ?: nbytes;
> @@ -3156,7 +3155,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
>   		return 0;
>   
>   	cpus_read_lock();
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   
>   	set_bit(CS_ONLINE, &cs->flags);
>   	if (is_spread_page(parent))
> @@ -3207,7 +3206,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
>   	cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
>   	spin_unlock_irq(&callback_lock);
>   out_unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
>   	return 0;
>   }
> @@ -3228,7 +3227,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
>   	struct cpuset *cs = css_cs(css);
>   
>   	cpus_read_lock();
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   
>   	if (is_partition_valid(cs))
>   		update_prstate(cs, 0);
> @@ -3247,7 +3246,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
>   	cpuset_dec();
>   	clear_bit(CS_ONLINE, &cs->flags);
>   
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
>   }
>   
> @@ -3260,7 +3259,7 @@ static void cpuset_css_free(struct cgroup_subsys_state *css)
>   
>   static void cpuset_bind(struct cgroup_subsys_state *root_css)
>   {
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	spin_lock_irq(&callback_lock);
>   
>   	if (is_in_v2_mode()) {
> @@ -3273,7 +3272,7 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)
>   	}
>   
>   	spin_unlock_irq(&callback_lock);
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   }
>   
>   /*
> @@ -3294,7 +3293,7 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
>   		return 0;
>   
>   	lockdep_assert_held(&cgroup_mutex);
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   
>   	/* Check to see if task is allowed in the cpuset */
>   	ret = cpuset_can_attach_check(cs);
> @@ -3315,7 +3314,7 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
>   	 */
>   	cs->attach_in_progress++;
>   out_unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   	return ret;
>   }
>   
> @@ -3331,11 +3330,11 @@ static void cpuset_cancel_fork(struct task_struct *task, struct css_set *cset)
>   	if (same_cs)
>   		return;
>   
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	cs->attach_in_progress--;
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   }
>   
>   /*
> @@ -3363,7 +3362,7 @@ static void cpuset_fork(struct task_struct *task)
>   	}
>   
>   	/* CLONE_INTO_CGROUP */
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
>   	cpuset_attach_task(cs, task);
>   
> @@ -3371,7 +3370,7 @@ static void cpuset_fork(struct task_struct *task)
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
>   
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   }
>   
>   struct cgroup_subsys cpuset_cgrp_subsys = {
> @@ -3472,7 +3471,7 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
>   	is_empty = cpumask_empty(cs->cpus_allowed) ||
>   		   nodes_empty(cs->mems_allowed);
>   
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   
>   	/*
>   	 * Move tasks to the nearest ancestor with execution resources,
> @@ -3482,7 +3481,7 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
>   	if (is_empty)
>   		remove_tasks_in_empty_cpuset(cs);
>   
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   }
>   
>   static void
> @@ -3533,14 +3532,14 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
>   retry:
>   	wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
>   
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   
>   	/*
>   	 * We have raced with task attaching. We wait until attaching
>   	 * is finished, so we won't attach a task to an empty cpuset.
>   	 */
>   	if (cs->attach_in_progress) {
> -		percpu_up_write(&cpuset_rwsem);
> +		mutex_unlock(&cpuset_mutex);
>   		goto retry;
>   	}
>   
> @@ -3637,7 +3636,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
>   					    cpus_updated, mems_updated);
>   
>   unlock:
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   }
>   
>   /**
> @@ -3667,7 +3666,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
>   	if (on_dfl && !alloc_cpumasks(NULL, &tmp))
>   		ptmp = &tmp;
>   
> -	percpu_down_write(&cpuset_rwsem);
> +	mutex_lock(&cpuset_mutex);
>   
>   	/* fetch the available cpus/mems and find out which changed how */
>   	cpumask_copy(&new_cpus, cpu_active_mask);
> @@ -3724,7 +3723,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
>   		update_tasks_nodemask(&top_cpuset);
>   	}
>   
> -	percpu_up_write(&cpuset_rwsem);
> +	mutex_unlock(&cpuset_mutex);
>   
>   	/* if cpus or mems changed, we need to propagate to descendants */
>   	if (cpus_updated || mems_updated) {
> @@ -4155,7 +4154,7 @@ void __cpuset_memory_pressure_bump(void)
>    *  - Used for /proc/<pid>/cpuset.
>    *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
>    *    doesn't really matter if tsk->cpuset changes after we read it,
> - *    and we take cpuset_rwsem, keeping cpuset_attach() from changing it
> + *    and we take cpuset_mutex, keeping cpuset_attach() from changing it
>    *    anyway.
>    */
>   int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 944c3ae39861..d826bec1c522 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7590,6 +7590,7 @@ static int __sched_setscheduler(struct task_struct *p,
>   	int reset_on_fork;
>   	int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
>   	struct rq *rq;
> +	bool cpuset_locked = false;
>   
>   	/* The pi code expects interrupts enabled */
>   	BUG_ON(pi && in_interrupt());
> @@ -7639,8 +7640,14 @@ static int __sched_setscheduler(struct task_struct *p,
>   			return retval;
>   	}
>   
> -	if (pi)
> -		cpuset_read_lock();
> +	/*
> +	 * SCHED_DEADLINE bandwidth accounting relies on stable cpusets
> +	 * information.
> +	 */
> +	if (dl_policy(policy) || dl_policy(p->policy)) {
> +		cpuset_locked = true;
> +		cpuset_lock();
> +	}
>   
>   	/*
>   	 * Make sure no PI-waiters arrive (or leave) while we are
> @@ -7716,8 +7723,8 @@ static int __sched_setscheduler(struct task_struct *p,
>   	if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
>   		policy = oldpolicy = -1;
>   		task_rq_unlock(rq, p, &rf);
> -		if (pi)
> -			cpuset_read_unlock();
> +		if (cpuset_locked)
> +			cpuset_unlock();
>   		goto recheck;
>   	}
>   
> @@ -7784,7 +7791,8 @@ static int __sched_setscheduler(struct task_struct *p,
>   	task_rq_unlock(rq, p, &rf);
>   
>   	if (pi) {
> -		cpuset_read_unlock();
> +		if (cpuset_locked)
> +			cpuset_unlock();
>   		rt_mutex_adjust_pi(p);
>   	}
>   
> @@ -7796,8 +7804,8 @@ static int __sched_setscheduler(struct task_struct *p,
>   
>   unlock:
>   	task_rq_unlock(rq, p, &rf);
> -	if (pi)
> -		cpuset_read_unlock();
> +	if (cpuset_locked)
> +		cpuset_unlock();
>   	return retval;
>   }
>   
Reviewed-by: Waiman Long <longman@redhat.com>

Re: [PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex

[Peter Zijlstra]

On Wed, May 03, 2023 at 09:22:24AM +0200, Juri Lelli wrote:

>  /*
> - * There are two global locks guarding cpuset structures - cpuset_rwsem and
> + * There are two global locks guarding cpuset structures - cpuset_mutex and
>   * callback_lock. We also require taking task_lock() when dereferencing a
>   * task's cpuset pointer. See "The task_lock() exception", at the end of this
> - * comment.  The cpuset code uses only cpuset_rwsem write lock.  Other
> - * kernel subsystems can use cpuset_read_lock()/cpuset_read_unlock() to
> - * prevent change to cpuset structures.
> + * comment.  The cpuset code uses only cpuset_mutex. Other kernel subsystems
> + * can use cpuset_lock()/cpuset_unlock() to prevent change to cpuset
> + * structures.
>   *
>   * A task must hold both locks to modify cpusets.  If a task holds
> - * cpuset_rwsem, it blocks others wanting that rwsem, ensuring that it
> - * is the only task able to also acquire callback_lock and be able to
> - * modify cpusets.  It can perform various checks on the cpuset structure
> - * first, knowing nothing will change.  It can also allocate memory while
> - * just holding cpuset_rwsem.  While it is performing these checks, various
> - * callback routines can briefly acquire callback_lock to query cpusets.
> - * Once it is ready to make the changes, it takes callback_lock, blocking
> - * everyone else.
> + * cpuset_mutex, it blocks others, ensuring that it is the only task able to
> + * also acquire callback_lock and be able to modify cpusets.  It can perform
> + * various checks on the cpuset structure first, knowing nothing will change.
> + * It can also allocate memory while just holding cpuset_mutex.  While it is
> + * performing these checks, various callback routines can briefly acquire
> + * callback_lock to query cpusets.  Once it is ready to make the changes, it
> + * takes callback_lock, blocking everyone else.
>   *
>   * Calls to the kernel memory allocator can not be made while holding
>   * callback_lock, as that would risk double tripping on callback_lock
> @@ -403,16 +402,16 @@ static struct cpuset top_cpuset = {
>   * guidelines for accessing subsystem state in kernel/cgroup.c
>   */
>  
> -DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
> +static DEFINE_MUTEX(cpuset_mutex);

Perhaps extend the comment to state you explicitly want a mutex for PI
etc.. ?

Re: [PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex

[Juri Lelli]

On 04/05/23 08:18, Peter Zijlstra wrote:
> On Wed, May 03, 2023 at 09:22:24AM +0200, Juri Lelli wrote:
> 
> >  /*
> > - * There are two global locks guarding cpuset structures - cpuset_rwsem and
> > + * There are two global locks guarding cpuset structures - cpuset_mutex and
> >   * callback_lock. We also require taking task_lock() when dereferencing a
> >   * task's cpuset pointer. See "The task_lock() exception", at the end of this
> > - * comment.  The cpuset code uses only cpuset_rwsem write lock.  Other
> > - * kernel subsystems can use cpuset_read_lock()/cpuset_read_unlock() to
> > - * prevent change to cpuset structures.
> > + * comment.  The cpuset code uses only cpuset_mutex. Other kernel subsystems
> > + * can use cpuset_lock()/cpuset_unlock() to prevent change to cpuset
> > + * structures.
> >   *
> >   * A task must hold both locks to modify cpusets.  If a task holds
> > - * cpuset_rwsem, it blocks others wanting that rwsem, ensuring that it
> > - * is the only task able to also acquire callback_lock and be able to
> > - * modify cpusets.  It can perform various checks on the cpuset structure
> > - * first, knowing nothing will change.  It can also allocate memory while
> > - * just holding cpuset_rwsem.  While it is performing these checks, various
> > - * callback routines can briefly acquire callback_lock to query cpusets.
> > - * Once it is ready to make the changes, it takes callback_lock, blocking
> > - * everyone else.
> > + * cpuset_mutex, it blocks others, ensuring that it is the only task able to
> > + * also acquire callback_lock and be able to modify cpusets.  It can perform
> > + * various checks on the cpuset structure first, knowing nothing will change.
> > + * It can also allocate memory while just holding cpuset_mutex.  While it is
> > + * performing these checks, various callback routines can briefly acquire
> > + * callback_lock to query cpusets.  Once it is ready to make the changes, it
> > + * takes callback_lock, blocking everyone else.
> >   *
> >   * Calls to the kernel memory allocator can not be made while holding
> >   * callback_lock, as that would risk double tripping on callback_lock
> > @@ -403,16 +402,16 @@ static struct cpuset top_cpuset = {
> >   * guidelines for accessing subsystem state in kernel/cgroup.c
> >   */
> >  
> > -DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
> > +static DEFINE_MUTEX(cpuset_mutex);
> 
> Perhaps extend the comment to state you explicitly want a mutex for PI
> etc.. ?
> 

Sure, can do that.

Thanks!

Re: [PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex

[Peter Zijlstra]

On Wed, May 03, 2023 at 09:22:24AM +0200, Juri Lelli wrote:
> Turns out percpu_cpuset_rwsem - commit 1243dc518c9d ("cgroup/cpuset:
> Convert cpuset_mutex to percpu_rwsem") - wasn't such a brilliant idea,
> as it has been reported to cause slowdowns in workloads that need to
> change cpuset configuration frequently and it is also not implementing
> priority inheritance (which causes troubles with realtime workloads).

What were they doing ? Dynamically adjusting the DL parameters?

Re: [PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex

[Juri Lelli]

On 04/05/23 08:21, Peter Zijlstra wrote:
> On Wed, May 03, 2023 at 09:22:24AM +0200, Juri Lelli wrote:
> > Turns out percpu_cpuset_rwsem - commit 1243dc518c9d ("cgroup/cpuset:
> > Convert cpuset_mutex to percpu_rwsem") - wasn't such a brilliant idea,
> > as it has been reported to cause slowdowns in workloads that need to
> > change cpuset configuration frequently and it is also not implementing
> > priority inheritance (which causes troubles with realtime workloads).
> 
> What were they doing ? Dynamically adjusting the DL parameters?
> 

Yes, calling sched_setattr to adjust params and/or add/remove DL
reservations.

[PATCH v2 3/6] sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets

[Juri Lelli]

Qais reported that iterating over all tasks when rebuilding root domains
for finding out which ones are DEADLINE and need their bandwidth
correctly restored on such root domains can be a costly operation (10+
ms delays on suspend-resume).

To fix the problem keep track of the number of DEADLINE tasks belonging
to each cpuset and then use this information (followup patch) to only
perform the above iteration if DEADLINE tasks are actually present in
the cpuset for which a corresponding root domain is being rebuilt.

Reported-by: Qais Yousef <qyousef@layalina.io>
Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 include/linux/cpuset.h  |  4 ++++
 kernel/cgroup/cgroup.c  |  4 ++++
 kernel/cgroup/cpuset.c  | 25 +++++++++++++++++++++++++
 kernel/sched/deadline.c | 14 ++++++++++++++
 4 files changed, 47 insertions(+)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index f90e6325d707..d629094fac6e 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -71,6 +71,8 @@ extern void cpuset_init_smp(void);
 extern void cpuset_force_rebuild(void);
 extern void cpuset_update_active_cpus(void);
 extern void cpuset_wait_for_hotplug(void);
+extern void inc_dl_tasks_cs(struct task_struct *task);
+extern void dec_dl_tasks_cs(struct task_struct *task);
 extern void cpuset_lock(void);
 extern void cpuset_unlock(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
@@ -189,6 +191,8 @@ static inline void cpuset_update_active_cpus(void)
 
 static inline void cpuset_wait_for_hotplug(void) { }
 
+static inline void inc_dl_tasks_cs(struct task_struct *task) { }
+static inline void dec_dl_tasks_cs(struct task_struct *task) { }
 static inline void cpuset_lock(void) { }
 static inline void cpuset_unlock(void) { }
 
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 625d7483951c..9d809191a54f 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -57,6 +57,7 @@
 #include <linux/file.h>
 #include <linux/fs_parser.h>
 #include <linux/sched/cputime.h>
+#include <linux/sched/deadline.h>
 #include <linux/psi.h>
 #include <net/sock.h>
 
@@ -6683,6 +6684,9 @@ void cgroup_exit(struct task_struct *tsk)
 	list_add_tail(&tsk->cg_list, &cset->dying_tasks);
 	cset->nr_tasks--;
 
+	if (dl_task(tsk))
+		dec_dl_tasks_cs(tsk);
+
 	WARN_ON_ONCE(cgroup_task_frozen(tsk));
 	if (unlikely(!(tsk->flags & PF_KTHREAD) &&
 		     test_bit(CGRP_FREEZE, &task_dfl_cgroup(tsk)->flags)))
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ee66be215fb9..b9f4d5602517 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -193,6 +193,12 @@ struct cpuset {
 	int use_parent_ecpus;
 	int child_ecpus_count;
 
+	/*
+	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
+	 * know when to rebuild associated root domain bandwidth information.
+	 */
+	int nr_deadline_tasks;
+
 	/* Invalid partition error code, not lock protected */
 	enum prs_errcode prs_err;
 
@@ -245,6 +251,20 @@ static inline struct cpuset *parent_cs(struct cpuset *cs)
 	return css_cs(cs->css.parent);
 }
 
+void inc_dl_tasks_cs(struct task_struct *p)
+{
+	struct cpuset *cs = task_cs(p);
+
+	cs->nr_deadline_tasks++;
+}
+
+void dec_dl_tasks_cs(struct task_struct *p)
+{
+	struct cpuset *cs = task_cs(p);
+
+	cs->nr_deadline_tasks--;
+}
+
 /* bits in struct cpuset flags field */
 typedef enum {
 	CS_ONLINE,
@@ -2497,6 +2517,11 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 		ret = security_task_setscheduler(task);
 		if (ret)
 			goto out_unlock;
+
+		if (dl_task(task)) {
+			cs->nr_deadline_tasks++;
+			cpuset_attach_old_cs->nr_deadline_tasks--;
+		}
 	}
 
 	/*
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 5a9a4b81c972..e11de074a6fd 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -16,6 +16,8 @@
  *                    Fabio Checconi <fchecconi@gmail.com>
  */
 
+#include <linux/cpuset.h>
+
 /*
  * Default limits for DL period; on the top end we guard against small util
  * tasks still getting ridiculously long effective runtimes, on the bottom end we
@@ -2596,6 +2598,12 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
 	if (task_on_rq_queued(p) && p->dl.dl_runtime)
 		task_non_contending(p);
 
+	/*
+	 * In case a task is setscheduled out from SCHED_DEADLINE we need to
+	 * keep track of that on its cpuset (for correct bandwidth tracking).
+	 */
+	dec_dl_tasks_cs(p);
+
 	if (!task_on_rq_queued(p)) {
 		/*
 		 * Inactive timer is armed. However, p is leaving DEADLINE and
@@ -2636,6 +2644,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 	if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
 		put_task_struct(p);
 
+	/*
+	 * In case a task is setscheduled to SCHED_DEADLINE we need to keep
+	 * track of that on its cpuset (for correct bandwidth tracking).
+	 */
+	inc_dl_tasks_cs(p);
+
 	/* If p is not queued we will update its parameters at next wakeup. */
 	if (!task_on_rq_queued(p)) {
 		add_rq_bw(&p->dl, &rq->dl);
-- 
2.40.1

Re: [PATCH v2 3/6] sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets

[Waiman Long]

On 5/3/23 03:22, Juri Lelli wrote:
> Qais reported that iterating over all tasks when rebuilding root domains
> for finding out which ones are DEADLINE and need their bandwidth
> correctly restored on such root domains can be a costly operation (10+
> ms delays on suspend-resume).
>
> To fix the problem keep track of the number of DEADLINE tasks belonging
> to each cpuset and then use this information (followup patch) to only
> perform the above iteration if DEADLINE tasks are actually present in
> the cpuset for which a corresponding root domain is being rebuilt.
>
> Reported-by: Qais Yousef <qyousef@layalina.io>
> Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
>   include/linux/cpuset.h  |  4 ++++
>   kernel/cgroup/cgroup.c  |  4 ++++
>   kernel/cgroup/cpuset.c  | 25 +++++++++++++++++++++++++
>   kernel/sched/deadline.c | 14 ++++++++++++++
>   4 files changed, 47 insertions(+)
>
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index f90e6325d707..d629094fac6e 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -71,6 +71,8 @@ extern void cpuset_init_smp(void);
>   extern void cpuset_force_rebuild(void);
>   extern void cpuset_update_active_cpus(void);
>   extern void cpuset_wait_for_hotplug(void);
> +extern void inc_dl_tasks_cs(struct task_struct *task);
> +extern void dec_dl_tasks_cs(struct task_struct *task);
>   extern void cpuset_lock(void);
>   extern void cpuset_unlock(void);
>   extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
> @@ -189,6 +191,8 @@ static inline void cpuset_update_active_cpus(void)
>   
>   static inline void cpuset_wait_for_hotplug(void) { }
>   
> +static inline void inc_dl_tasks_cs(struct task_struct *task) { }
> +static inline void dec_dl_tasks_cs(struct task_struct *task) { }
>   static inline void cpuset_lock(void) { }
>   static inline void cpuset_unlock(void) { }
>   
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 625d7483951c..9d809191a54f 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -57,6 +57,7 @@
>   #include <linux/file.h>
>   #include <linux/fs_parser.h>
>   #include <linux/sched/cputime.h>
> +#include <linux/sched/deadline.h>
>   #include <linux/psi.h>
>   #include <net/sock.h>
>   
> @@ -6683,6 +6684,9 @@ void cgroup_exit(struct task_struct *tsk)
>   	list_add_tail(&tsk->cg_list, &cset->dying_tasks);
>   	cset->nr_tasks--;
>   
> +	if (dl_task(tsk))
> +		dec_dl_tasks_cs(tsk);
> +
>   	WARN_ON_ONCE(cgroup_task_frozen(tsk));
>   	if (unlikely(!(tsk->flags & PF_KTHREAD) &&
>   		     test_bit(CGRP_FREEZE, &task_dfl_cgroup(tsk)->flags)))
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index ee66be215fb9..b9f4d5602517 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -193,6 +193,12 @@ struct cpuset {
>   	int use_parent_ecpus;
>   	int child_ecpus_count;
>   
> +	/*
> +	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
> +	 * know when to rebuild associated root domain bandwidth information.
> +	 */
> +	int nr_deadline_tasks;
> +
>   	/* Invalid partition error code, not lock protected */
>   	enum prs_errcode prs_err;
>   
> @@ -245,6 +251,20 @@ static inline struct cpuset *parent_cs(struct cpuset *cs)
>   	return css_cs(cs->css.parent);
>   }
>   
> +void inc_dl_tasks_cs(struct task_struct *p)
> +{
> +	struct cpuset *cs = task_cs(p);
> +
> +	cs->nr_deadline_tasks++;
> +}
> +
> +void dec_dl_tasks_cs(struct task_struct *p)
> +{
> +	struct cpuset *cs = task_cs(p);
> +
> +	cs->nr_deadline_tasks--;
> +}
> +
>   /* bits in struct cpuset flags field */
>   typedef enum {
>   	CS_ONLINE,
> @@ -2497,6 +2517,11 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>   		ret = security_task_setscheduler(task);
>   		if (ret)
>   			goto out_unlock;
> +
> +		if (dl_task(task)) {
> +			cs->nr_deadline_tasks++;
> +			cpuset_attach_old_cs->nr_deadline_tasks--;
> +		}
>   	}
>   
>   	/*
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 5a9a4b81c972..e11de074a6fd 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -16,6 +16,8 @@
>    *                    Fabio Checconi <fchecconi@gmail.com>
>    */
>   
> +#include <linux/cpuset.h>
> +
>   /*
>    * Default limits for DL period; on the top end we guard against small util
>    * tasks still getting ridiculously long effective runtimes, on the bottom end we
> @@ -2596,6 +2598,12 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
>   	if (task_on_rq_queued(p) && p->dl.dl_runtime)
>   		task_non_contending(p);
>   
> +	/*
> +	 * In case a task is setscheduled out from SCHED_DEADLINE we need to
> +	 * keep track of that on its cpuset (for correct bandwidth tracking).
> +	 */
> +	dec_dl_tasks_cs(p);
> +
>   	if (!task_on_rq_queued(p)) {
>   		/*
>   		 * Inactive timer is armed. However, p is leaving DEADLINE and
> @@ -2636,6 +2644,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
>   	if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
>   		put_task_struct(p);
>   
> +	/*
> +	 * In case a task is setscheduled to SCHED_DEADLINE we need to keep
> +	 * track of that on its cpuset (for correct bandwidth tracking).
> +	 */
> +	inc_dl_tasks_cs(p);
> +
>   	/* If p is not queued we will update its parameters at next wakeup. */
>   	if (!task_on_rq_queued(p)) {
>   		add_rq_bw(&p->dl, &rq->dl);
Reviewed-by: Waiman Long <longman@redhat.com>

[PATCH v2 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present

[Juri Lelli]

update_tasks_root_domain currently iterates over all tasks even if no
DEADLINE task is present on the cpuset/root domain for which bandwidth
accounting is being rebuilt. This has been reported to introduce 10+ ms
delays on suspend-resume operations.

Skip the costly iteration for cpusets that don't contain DEADLINE tasks.

Reported-by: Qais Yousef <qyousef@layalina.io>
Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 kernel/cgroup/cpuset.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index b9f4d5602517..6587df42cb61 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1090,6 +1090,9 @@ static void dl_update_tasks_root_domain(struct cpuset *cs)
 	struct css_task_iter it;
 	struct task_struct *task;
 
+	if (cs->nr_deadline_tasks == 0)
+		return;
+
 	css_task_iter_start(&cs->css, 0, &it);
 
 	while ((task = css_task_iter_next(&it)))
-- 
2.40.1

Re: [PATCH v2 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present

[Waiman Long]

On 5/3/23 03:22, Juri Lelli wrote:
> update_tasks_root_domain currently iterates over all tasks even if no
> DEADLINE task is present on the cpuset/root domain for which bandwidth
> accounting is being rebuilt. This has been reported to introduce 10+ ms
> delays on suspend-resume operations.
>
> Skip the costly iteration for cpusets that don't contain DEADLINE tasks.
>
> Reported-by: Qais Yousef <qyousef@layalina.io>
> Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
>   kernel/cgroup/cpuset.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index b9f4d5602517..6587df42cb61 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1090,6 +1090,9 @@ static void dl_update_tasks_root_domain(struct cpuset *cs)
>   	struct css_task_iter it;
>   	struct task_struct *task;
>   
> +	if (cs->nr_deadline_tasks == 0)
> +		return;
> +
>   	css_task_iter_start(&cs->css, 0, &it);
>   
>   	while ((task = css_task_iter_next(&it)))
Reviewed-by: Waiman Long <longman@redhat.com>

[PATCH v2 5/6] sched/deadline: Create DL BW alloc, free & check overflow interface

[Juri Lelli]

From: Dietmar Eggemann <dietmar.eggemann@arm.com>

Rework the existing dl_cpu_busy() interface which offers DL BW overflow
checking and per-task DL BW allocation.

Add dl_bw_free() as an interface to be able to free DL BW.
It will be used to allow freeing of the DL BW request done during
cpuset_can_attach() in case multiple controllers are attached to the
cgroup next to the cpuset controller and one of the non-cpuset
can_attach() fails.

dl_bw_alloc() (and dl_bw_free()) now take a `u64 dl_bw` parameter
instead of `struct task_struct *p` used in dl_cpu_busy().  This allows
to allocate DL BW for a set of tasks too rater than only for a single
task.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 include/linux/sched.h   |  2 ++
 kernel/sched/core.c     |  4 ++--
 kernel/sched/deadline.c | 53 +++++++++++++++++++++++++++++++----------
 kernel/sched/sched.h    |  2 +-
 4 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index eed5d65b8d1f..0bee06542450 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1853,6 +1853,8 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
 
 extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
 extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
+extern int dl_bw_alloc(int cpu, u64 dl_bw);
+extern void dl_bw_free(int cpu, u64 dl_bw);
 #ifdef CONFIG_SMP
 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d826bec1c522..df659892d7d5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9319,7 +9319,7 @@ int task_can_attach(struct task_struct *p,
 
 		if (unlikely(cpu >= nr_cpu_ids))
 			return -EINVAL;
-		ret = dl_cpu_busy(cpu, p);
+		ret = dl_bw_alloc(cpu, p->dl.dl_bw);
 	}
 
 out:
@@ -9604,7 +9604,7 @@ static void cpuset_cpu_active(void)
 static int cpuset_cpu_inactive(unsigned int cpu)
 {
 	if (!cpuhp_tasks_frozen) {
-		int ret = dl_cpu_busy(cpu, NULL);
+		int ret = dl_bw_check_overflow(cpu);
 
 		if (ret)
 			return ret;
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e11de074a6fd..166c3e6eae61 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -3058,26 +3058,38 @@ int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur,
 	return ret;
 }
 
-int dl_cpu_busy(int cpu, struct task_struct *p)
+enum dl_bw_request {
+	dl_bw_req_check_overflow = 0,
+	dl_bw_req_alloc,
+	dl_bw_req_free
+};
+
+static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw)
 {
-	unsigned long flags, cap;
+	unsigned long flags;
 	struct dl_bw *dl_b;
-	bool overflow;
+	bool overflow = 0;
 
 	rcu_read_lock_sched();
 	dl_b = dl_bw_of(cpu);
 	raw_spin_lock_irqsave(&dl_b->lock, flags);
-	cap = dl_bw_capacity(cpu);
-	overflow = __dl_overflow(dl_b, cap, 0, p ? p->dl.dl_bw : 0);
 
-	if (!overflow && p) {
-		/*
-		 * We reserve space for this task in the destination
-		 * root_domain, as we can't fail after this point.
-		 * We will free resources in the source root_domain
-		 * later on (see set_cpus_allowed_dl()).
-		 */
-		__dl_add(dl_b, p->dl.dl_bw, dl_bw_cpus(cpu));
+	if (req == dl_bw_req_free) {
+		__dl_sub(dl_b, dl_bw, dl_bw_cpus(cpu));
+	} else {
+		unsigned long cap = dl_bw_capacity(cpu);
+
+		overflow = __dl_overflow(dl_b, cap, 0, dl_bw);
+
+		if (req == dl_bw_req_alloc && !overflow) {
+			/*
+			 * We reserve space in the destination
+			 * root_domain, as we can't fail after this point.
+			 * We will free resources in the source root_domain
+			 * later on (see set_cpus_allowed_dl()).
+			 */
+			__dl_add(dl_b, dl_bw, dl_bw_cpus(cpu));
+		}
 	}
 
 	raw_spin_unlock_irqrestore(&dl_b->lock, flags);
@@ -3085,6 +3097,21 @@ int dl_cpu_busy(int cpu, struct task_struct *p)
 
 	return overflow ? -EBUSY : 0;
 }
+
+int dl_bw_check_overflow(int cpu)
+{
+	return dl_bw_manage(dl_bw_req_check_overflow, cpu, 0);
+}
+
+int dl_bw_alloc(int cpu, u64 dl_bw)
+{
+	return dl_bw_manage(dl_bw_req_alloc, cpu, dl_bw);
+}
+
+void dl_bw_free(int cpu, u64 dl_bw)
+{
+	dl_bw_manage(dl_bw_req_free, cpu, dl_bw);
+}
 #endif
 
 #ifdef CONFIG_SCHED_DEBUG
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ec7b3e0a2b20..0ad712811e35 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -330,7 +330,7 @@ extern void __getparam_dl(struct task_struct *p, struct sched_attr *attr);
 extern bool __checkparam_dl(const struct sched_attr *attr);
 extern bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr);
 extern int  dl_cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
-extern int  dl_cpu_busy(int cpu, struct task_struct *p);
+extern int  dl_bw_check_overflow(int cpu);
 
 #ifdef CONFIG_CGROUP_SCHED
 
-- 
2.40.1

Re: [PATCH v2 5/6] sched/deadline: Create DL BW alloc, free & check overflow interface

[Waiman Long]

On 5/3/23 03:22, Juri Lelli wrote:
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
>
> Rework the existing dl_cpu_busy() interface which offers DL BW overflow
> checking and per-task DL BW allocation.
>
> Add dl_bw_free() as an interface to be able to free DL BW.
> It will be used to allow freeing of the DL BW request done during
> cpuset_can_attach() in case multiple controllers are attached to the
> cgroup next to the cpuset controller and one of the non-cpuset
> can_attach() fails.
>
> dl_bw_alloc() (and dl_bw_free()) now take a `u64 dl_bw` parameter
> instead of `struct task_struct *p` used in dl_cpu_busy().  This allows
> to allocate DL BW for a set of tasks too rater than only for a single

Typo: "rater" => "rather".

Cheers,
Longman

Re: [PATCH v2 5/6] sched/deadline: Create DL BW alloc, free & check overflow interface

[Peter Zijlstra]

On Wed, May 03, 2023 at 09:22:27AM +0200, Juri Lelli wrote:
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
> 
> Rework the existing dl_cpu_busy() interface which offers DL BW overflow
> checking and per-task DL BW allocation.
> 
> Add dl_bw_free() as an interface to be able to free DL BW.
> It will be used to allow freeing of the DL BW request done during
> cpuset_can_attach() in case multiple controllers are attached to the
> cgroup next to the cpuset controller and one of the non-cpuset
> can_attach() fails.
> 
> dl_bw_alloc() (and dl_bw_free()) now take a `u64 dl_bw` parameter
> instead of `struct task_struct *p` used in dl_cpu_busy().  This allows
> to allocate DL BW for a set of tasks too rater than only for a single
> task.
> 

Changlog fails the 'why' test.

Re: [PATCH v2 5/6] sched/deadline: Create DL BW alloc, free & check overflow interface

[Juri Lelli]

On 04/05/23 08:23, Peter Zijlstra wrote:
> On Wed, May 03, 2023 at 09:22:27AM +0200, Juri Lelli wrote:
> > From: Dietmar Eggemann <dietmar.eggemann@arm.com>
> > 
> > Rework the existing dl_cpu_busy() interface which offers DL BW overflow
> > checking and per-task DL BW allocation.
> > 
> > Add dl_bw_free() as an interface to be able to free DL BW.
> > It will be used to allow freeing of the DL BW request done during
> > cpuset_can_attach() in case multiple controllers are attached to the
> > cgroup next to the cpuset controller and one of the non-cpuset
> > can_attach() fails.
> > 
> > dl_bw_alloc() (and dl_bw_free()) now take a `u64 dl_bw` parameter
> > instead of `struct task_struct *p` used in dl_cpu_busy().  This allows
> > to allocate DL BW for a set of tasks too rater than only for a single
> > task.
> > 
> 
> Changlog fails the 'why' test.
> 

Dietmar, if you could please add (or rework) the 'why' as a reply to
this email, I can fold in v3.

Thanks!

Re: [PATCH v2 5/6] sched/deadline: Create DL BW alloc, free & check overflow interface

[Dietmar Eggemann]

On 04/05/2023 10:15, Juri Lelli wrote:
> On 04/05/23 08:23, Peter Zijlstra wrote:
>> On Wed, May 03, 2023 at 09:22:27AM +0200, Juri Lelli wrote:
>>> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
>>>
>>> Rework the existing dl_cpu_busy() interface which offers DL BW overflow
>>> checking and per-task DL BW allocation.
>>>
>>> Add dl_bw_free() as an interface to be able to free DL BW.
>>> It will be used to allow freeing of the DL BW request done during
>>> cpuset_can_attach() in case multiple controllers are attached to the
>>> cgroup next to the cpuset controller and one of the non-cpuset
>>> can_attach() fails.
>>>
>>> dl_bw_alloc() (and dl_bw_free()) now take a `u64 dl_bw` parameter
>>> instead of `struct task_struct *p` used in dl_cpu_busy().  This allows
>>> to allocate DL BW for a set of tasks too rater than only for a single
>>> task.
>>>
>>
>> Changlog fails the 'why' test.
>>
> 
> Dietmar, if you could please add (or rework) the 'why' as a reply to
> this email, I can fold in v3.
> 
> Thanks!
> 

-->8--

From 4ce3556723728a606b527bef8813b0fce3ad6e22 Mon Sep 17 00:00:00 2001
From: Dietmar Eggemann <dietmar.eggemann@arm.com>
Date: Wed, 3 May 2023 09:22:27 +0200
Subject: [PATCH] sched/deadline: Create DL BW alloc, free & check overflow
 interface

While moving a set of tasks between exclusive cpusets,
cpuset_can_attach() -> task_can_attach() calls dl_cpu_busy(..., p) for
DL BW overflow checking and per-task DL BW allocation on the destination
root_domain for the DL tasks in this set.

This approach has the issue of not freeing already allocated DL BW in
the following error cases:

(1) The set of tasks includes multiple DL tasks and DL BW overflow
    checking fails for one of the subsequent DL tasks.

(2) Another controller next to the cpuset controller which is attached
    to the same cgroup fails in its can_attach().

To address this problem rework dl_cpu_busy():

(1) Split it into dl_bw_check_overflow() & dl_bw_alloc() and add a
    dedicated dl_bw_free().

(2) dl_bw_alloc() & dl_bw_free() take a `u64 dl_bw` parameter instead of
    a `struct task_struct *p` used in dl_cpu_busy(). This allows to
    allocate DL BW for a set of tasks too rather than only for a single
    task.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 include/linux/sched.h   |  2 ++
 kernel/sched/core.c     |  4 ++--
 kernel/sched/deadline.c | 53 +++++++++++++++++++++++++++++++----------
 kernel/sched/sched.h    |  2 +-
 4 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index eed5d65b8d1f..0bee06542450 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1853,6 +1853,8 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
 
 extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
 extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
+extern int dl_bw_alloc(int cpu, u64 dl_bw);
+extern void dl_bw_free(int cpu, u64 dl_bw);
 #ifdef CONFIG_SMP
 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d826bec1c522..df659892d7d5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9319,7 +9319,7 @@ int task_can_attach(struct task_struct *p,
 
 		if (unlikely(cpu >= nr_cpu_ids))
 			return -EINVAL;
-		ret = dl_cpu_busy(cpu, p);
+		ret = dl_bw_alloc(cpu, p->dl.dl_bw);
 	}
 
 out:
@@ -9604,7 +9604,7 @@ static void cpuset_cpu_active(void)
 static int cpuset_cpu_inactive(unsigned int cpu)
 {
 	if (!cpuhp_tasks_frozen) {
-		int ret = dl_cpu_busy(cpu, NULL);
+		int ret = dl_bw_check_overflow(cpu);
 
 		if (ret)
 			return ret;
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e11de074a6fd..166c3e6eae61 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -3058,26 +3058,38 @@ int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur,
 	return ret;
 }
 
-int dl_cpu_busy(int cpu, struct task_struct *p)
+enum dl_bw_request {
+	dl_bw_req_check_overflow = 0,
+	dl_bw_req_alloc,
+	dl_bw_req_free
+};
+
+static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw)
 {
-	unsigned long flags, cap;
+	unsigned long flags;
 	struct dl_bw *dl_b;
-	bool overflow;
+	bool overflow = 0;
 
 	rcu_read_lock_sched();
 	dl_b = dl_bw_of(cpu);
 	raw_spin_lock_irqsave(&dl_b->lock, flags);
-	cap = dl_bw_capacity(cpu);
-	overflow = __dl_overflow(dl_b, cap, 0, p ? p->dl.dl_bw : 0);
 
-	if (!overflow && p) {
-		/*
-		 * We reserve space for this task in the destination
-		 * root_domain, as we can't fail after this point.
-		 * We will free resources in the source root_domain
-		 * later on (see set_cpus_allowed_dl()).
-		 */
-		__dl_add(dl_b, p->dl.dl_bw, dl_bw_cpus(cpu));
+	if (req == dl_bw_req_free) {
+		__dl_sub(dl_b, dl_bw, dl_bw_cpus(cpu));
+	} else {
+		unsigned long cap = dl_bw_capacity(cpu);
+
+		overflow = __dl_overflow(dl_b, cap, 0, dl_bw);
+
+		if (req == dl_bw_req_alloc && !overflow) {
+			/*
+			 * We reserve space in the destination
+			 * root_domain, as we can't fail after this point.
+			 * We will free resources in the source root_domain
+			 * later on (see set_cpus_allowed_dl()).
+			 */
+			__dl_add(dl_b, dl_bw, dl_bw_cpus(cpu));
+		}
 	}
 
 	raw_spin_unlock_irqrestore(&dl_b->lock, flags);
@@ -3085,6 +3097,21 @@ int dl_cpu_busy(int cpu, struct task_struct *p)
 
 	return overflow ? -EBUSY : 0;
 }
+
+int dl_bw_check_overflow(int cpu)
+{
+	return dl_bw_manage(dl_bw_req_check_overflow, cpu, 0);
+}
+
+int dl_bw_alloc(int cpu, u64 dl_bw)
+{
+	return dl_bw_manage(dl_bw_req_alloc, cpu, dl_bw);
+}
+
+void dl_bw_free(int cpu, u64 dl_bw)
+{
+	dl_bw_manage(dl_bw_req_free, cpu, dl_bw);
+}
 #endif
 
 #ifdef CONFIG_SCHED_DEBUG
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ec7b3e0a2b20..0ad712811e35 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -330,7 +330,7 @@ extern void __getparam_dl(struct task_struct *p, struct sched_attr *attr);
 extern bool __checkparam_dl(const struct sched_attr *attr);
 extern bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr);
 extern int  dl_cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
-extern int  dl_cpu_busy(int cpu, struct task_struct *p);
+extern int  dl_bw_check_overflow(int cpu);
 
 #ifdef CONFIG_CGROUP_SCHED
 
-- 
2.25.1

[PATCH v2 6/6] cgroup/cpuset: Free DL BW in case can_attach() fails

[Juri Lelli]

From: Dietmar Eggemann <dietmar.eggemann@arm.com>

cpuset_can_attach() can fail. Postpone DL BW allocation until all tasks
have been checked. DL BW is not allocated per-task but as a sum over
all DL tasks migrating.

If multiple controllers are attached to the cgroup next to the cpuset
controller a non-cpuset can_attach() can fail. In this case free DL BW
in cpuset_cancel_attach().

Finally, update cpuset DL task count (nr_deadline_tasks) only in
cpuset_attach().

Suggested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 include/linux/sched.h  |  2 +-
 kernel/cgroup/cpuset.c | 53 ++++++++++++++++++++++++++++++++++++++----
 kernel/sched/core.c    | 17 ++------------
 3 files changed, 51 insertions(+), 21 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0bee06542450..2553918f0b61 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1852,7 +1852,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
 }
 
 extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
-extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
+extern int task_can_attach(struct task_struct *p);
 extern int dl_bw_alloc(int cpu, u64 dl_bw);
 extern void dl_bw_free(int cpu, u64 dl_bw);
 #ifdef CONFIG_SMP
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 6587df42cb61..d1073603c96c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -198,6 +198,8 @@ struct cpuset {
 	 * know when to rebuild associated root domain bandwidth information.
 	 */
 	int nr_deadline_tasks;
+	int nr_migrate_dl_tasks;
+	u64 sum_migrate_dl_bw;
 
 	/* Invalid partition error code, not lock protected */
 	enum prs_errcode prs_err;
@@ -2494,16 +2496,23 @@ static int cpuset_can_attach_check(struct cpuset *cs)
 	return 0;
 }
 
+static void reset_migrate_dl_data(struct cpuset *cs)
+{
+	cs->nr_migrate_dl_tasks = 0;
+	cs->sum_migrate_dl_bw = 0;
+}
+
 /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
 static int cpuset_can_attach(struct cgroup_taskset *tset)
 {
 	struct cgroup_subsys_state *css;
-	struct cpuset *cs;
+	struct cpuset *cs, *oldcs;
 	struct task_struct *task;
 	int ret;
 
 	/* used later by cpuset_attach() */
 	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
+	oldcs = cpuset_attach_old_cs;
 	cs = css_cs(css);
 
 	mutex_lock(&cpuset_mutex);
@@ -2514,7 +2523,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 		goto out_unlock;
 
 	cgroup_taskset_for_each(task, css, tset) {
-		ret = task_can_attach(task, cs->effective_cpus);
+		ret = task_can_attach(task);
 		if (ret)
 			goto out_unlock;
 		ret = security_task_setscheduler(task);
@@ -2522,11 +2531,31 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 			goto out_unlock;
 
 		if (dl_task(task)) {
-			cs->nr_deadline_tasks++;
-			cpuset_attach_old_cs->nr_deadline_tasks--;
+			cs->nr_migrate_dl_tasks++;
+			cs->sum_migrate_dl_bw += task->dl.dl_bw;
 		}
 	}
 
+	if (!cs->nr_migrate_dl_tasks)
+		goto out_success;
+
+	if (!cpumask_intersects(oldcs->effective_cpus, cs->effective_cpus)) {
+		int cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
+
+		if (unlikely(cpu >= nr_cpu_ids)) {
+			reset_migrate_dl_data(cs);
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
+		ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
+		if (ret) {
+			reset_migrate_dl_data(cs);
+			goto out_unlock;
+		}
+	}
+
+out_success:
 	/*
 	 * Mark attach is in progress.  This makes validate_change() fail
 	 * changes which zero cpus/mems_allowed.
@@ -2549,6 +2578,14 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 	cs->attach_in_progress--;
 	if (!cs->attach_in_progress)
 		wake_up(&cpuset_attach_wq);
+
+	if (cs->nr_migrate_dl_tasks) {
+		int cpu = cpumask_any(cs->effective_cpus);
+
+		dl_bw_free(cpu, cs->sum_migrate_dl_bw);
+		reset_migrate_dl_data(cs);
+	}
+
 	mutex_unlock(&cpuset_mutex);
 }
 
@@ -2649,6 +2686,12 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 out:
 	cs->old_mems_allowed = cpuset_attach_nodemask_to;
 
+	if (cs->nr_migrate_dl_tasks) {
+		cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks;
+		oldcs->nr_deadline_tasks -= cs->nr_migrate_dl_tasks;
+		reset_migrate_dl_data(cs);
+	}
+
 	cs->attach_in_progress--;
 	if (!cs->attach_in_progress)
 		wake_up(&cpuset_attach_wq);
@@ -3328,7 +3371,7 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
 	if (ret)
 		goto out_unlock;
 
-	ret = task_can_attach(task, cs->effective_cpus);
+	ret = task_can_attach(task);
 	if (ret)
 		goto out_unlock;
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df659892d7d5..ed0d7381b2ec 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9294,8 +9294,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
 	return ret;
 }
 
-int task_can_attach(struct task_struct *p,
-		    const struct cpumask *cs_effective_cpus)
+int task_can_attach(struct task_struct *p)
 {
 	int ret = 0;
 
@@ -9308,21 +9307,9 @@ int task_can_attach(struct task_struct *p,
 	 * success of set_cpus_allowed_ptr() on all attached tasks
 	 * before cpus_mask may be changed.
 	 */
-	if (p->flags & PF_NO_SETAFFINITY) {
+	if (p->flags & PF_NO_SETAFFINITY)
 		ret = -EINVAL;
-		goto out;
-	}
-
-	if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
-					      cs_effective_cpus)) {
-		int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);
 
-		if (unlikely(cpu >= nr_cpu_ids))
-			return -EINVAL;
-		ret = dl_bw_alloc(cpu, p->dl.dl_bw);
-	}
-
-out:
 	return ret;
 }
 
-- 
2.40.1

Re: [PATCH v2 6/6] cgroup/cpuset: Free DL BW in case can_attach() fails

[Waiman Long]

On 5/3/23 03:22, Juri Lelli wrote:
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
>
> cpuset_can_attach() can fail. Postpone DL BW allocation until all tasks
> have been checked. DL BW is not allocated per-task but as a sum over
> all DL tasks migrating.
>
> If multiple controllers are attached to the cgroup next to the cpuset
> controller a non-cpuset can_attach() can fail. In this case free DL BW
> in cpuset_cancel_attach().
>
> Finally, update cpuset DL task count (nr_deadline_tasks) only in
> cpuset_attach().
>
> Suggested-by: Waiman Long <longman@redhat.com>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
>   include/linux/sched.h  |  2 +-
>   kernel/cgroup/cpuset.c | 53 ++++++++++++++++++++++++++++++++++++++----
>   kernel/sched/core.c    | 17 ++------------
>   3 files changed, 51 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 0bee06542450..2553918f0b61 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1852,7 +1852,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
>   }
>   
>   extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
> -extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
> +extern int task_can_attach(struct task_struct *p);
>   extern int dl_bw_alloc(int cpu, u64 dl_bw);
>   extern void dl_bw_free(int cpu, u64 dl_bw);
>   #ifdef CONFIG_SMP
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 6587df42cb61..d1073603c96c 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -198,6 +198,8 @@ struct cpuset {
>   	 * know when to rebuild associated root domain bandwidth information.
>   	 */
>   	int nr_deadline_tasks;
> +	int nr_migrate_dl_tasks;
> +	u64 sum_migrate_dl_bw;
>   
>   	/* Invalid partition error code, not lock protected */
>   	enum prs_errcode prs_err;
> @@ -2494,16 +2496,23 @@ static int cpuset_can_attach_check(struct cpuset *cs)
>   	return 0;
>   }
>   
> +static void reset_migrate_dl_data(struct cpuset *cs)
> +{
> +	cs->nr_migrate_dl_tasks = 0;
> +	cs->sum_migrate_dl_bw = 0;
> +}
> +
>   /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
>   static int cpuset_can_attach(struct cgroup_taskset *tset)
>   {
>   	struct cgroup_subsys_state *css;
> -	struct cpuset *cs;
> +	struct cpuset *cs, *oldcs;
>   	struct task_struct *task;
>   	int ret;
>   
>   	/* used later by cpuset_attach() */
>   	cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
> +	oldcs = cpuset_attach_old_cs;
>   	cs = css_cs(css);
>   
>   	mutex_lock(&cpuset_mutex);
> @@ -2514,7 +2523,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>   		goto out_unlock;
>   
>   	cgroup_taskset_for_each(task, css, tset) {
> -		ret = task_can_attach(task, cs->effective_cpus);
> +		ret = task_can_attach(task);
>   		if (ret)
>   			goto out_unlock;
>   		ret = security_task_setscheduler(task);
> @@ -2522,11 +2531,31 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
>   			goto out_unlock;
>   
>   		if (dl_task(task)) {
> -			cs->nr_deadline_tasks++;
> -			cpuset_attach_old_cs->nr_deadline_tasks--;
> +			cs->nr_migrate_dl_tasks++;
> +			cs->sum_migrate_dl_bw += task->dl.dl_bw;
>   		}
>   	}
>   
> +	if (!cs->nr_migrate_dl_tasks)
> +		goto out_success;
> +
> +	if (!cpumask_intersects(oldcs->effective_cpus, cs->effective_cpus)) {
> +		int cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
> +
> +		if (unlikely(cpu >= nr_cpu_ids)) {
> +			reset_migrate_dl_data(cs);
> +			ret = -EINVAL;
> +			goto out_unlock;
> +		}
> +
> +		ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
> +		if (ret) {
> +			reset_migrate_dl_data(cs);
> +			goto out_unlock;
> +		}
> +	}
> +
> +out_success:
>   	/*
>   	 * Mark attach is in progress.  This makes validate_change() fail
>   	 * changes which zero cpus/mems_allowed.
> @@ -2549,6 +2578,14 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
>   	cs->attach_in_progress--;
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
> +
> +	if (cs->nr_migrate_dl_tasks) {
> +		int cpu = cpumask_any(cs->effective_cpus);
> +
> +		dl_bw_free(cpu, cs->sum_migrate_dl_bw);
> +		reset_migrate_dl_data(cs);
> +	}
> +
>   	mutex_unlock(&cpuset_mutex);
>   }
>   
> @@ -2649,6 +2686,12 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>   out:
>   	cs->old_mems_allowed = cpuset_attach_nodemask_to;
>   
> +	if (cs->nr_migrate_dl_tasks) {
> +		cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks;
> +		oldcs->nr_deadline_tasks -= cs->nr_migrate_dl_tasks;
> +		reset_migrate_dl_data(cs);
> +	}
> +
>   	cs->attach_in_progress--;
>   	if (!cs->attach_in_progress)
>   		wake_up(&cpuset_attach_wq);
> @@ -3328,7 +3371,7 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset)
>   	if (ret)
>   		goto out_unlock;
>   
> -	ret = task_can_attach(task, cs->effective_cpus);
> +	ret = task_can_attach(task);
>   	if (ret)
>   		goto out_unlock;
>   
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index df659892d7d5..ed0d7381b2ec 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9294,8 +9294,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
>   	return ret;
>   }
>   
> -int task_can_attach(struct task_struct *p,
> -		    const struct cpumask *cs_effective_cpus)
> +int task_can_attach(struct task_struct *p)
>   {
>   	int ret = 0;
>   
> @@ -9308,21 +9307,9 @@ int task_can_attach(struct task_struct *p,
>   	 * success of set_cpus_allowed_ptr() on all attached tasks
>   	 * before cpus_mask may be changed.
>   	 */
> -	if (p->flags & PF_NO_SETAFFINITY) {
> +	if (p->flags & PF_NO_SETAFFINITY)
>   		ret = -EINVAL;
> -		goto out;
> -	}
> -
> -	if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
> -					      cs_effective_cpus)) {
> -		int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);
>   
> -		if (unlikely(cpu >= nr_cpu_ids))
> -			return -EINVAL;
> -		ret = dl_bw_alloc(cpu, p->dl.dl_bw);
> -	}
> -
> -out:
>   	return ret;
>   }
>   
Reviewed-by: Waiman Long <longman@redhat.com>

Re: [PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

[Peter Zijlstra]

On Wed, May 03, 2023 at 09:22:22AM +0200, Juri Lelli wrote:

> Dietmar Eggemann (2):
>   sched/deadline: Create DL BW alloc, free & check overflow interface
>   cgroup/cpuset: Free DL BW in case can_attach() fails
> 
> Juri Lelli (4):
>   cgroup/cpuset: Rename functions dealing with DEADLINE accounting
>   sched/cpuset: Bring back cpuset_mutex
>   sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets
>   cgroup/cpuset: Iterate only if DEADLINE tasks are present
> 
>  include/linux/cpuset.h  |  12 +-
>  include/linux/sched.h   |   4 +-
>  kernel/cgroup/cgroup.c  |   4 +
>  kernel/cgroup/cpuset.c  | 242 ++++++++++++++++++++++++++--------------
>  kernel/sched/core.c     |  41 +++----
>  kernel/sched/deadline.c |  67 ++++++++---
>  kernel/sched/sched.h    |   2 +-
>  7 files changed, 244 insertions(+), 128 deletions(-)

Aside from a few niggles, these look fine to me. Who were you expecting
to merge these, tj or me?

Re: [PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

[Juri Lelli]

On 04/05/23 08:25, Peter Zijlstra wrote:
> On Wed, May 03, 2023 at 09:22:22AM +0200, Juri Lelli wrote:
> 
> > Dietmar Eggemann (2):
> >   sched/deadline: Create DL BW alloc, free & check overflow interface
> >   cgroup/cpuset: Free DL BW in case can_attach() fails
> > 
> > Juri Lelli (4):
> >   cgroup/cpuset: Rename functions dealing with DEADLINE accounting
> >   sched/cpuset: Bring back cpuset_mutex
> >   sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets
> >   cgroup/cpuset: Iterate only if DEADLINE tasks are present
> > 
> >  include/linux/cpuset.h  |  12 +-
> >  include/linux/sched.h   |   4 +-
> >  kernel/cgroup/cgroup.c  |   4 +
> >  kernel/cgroup/cpuset.c  | 242 ++++++++++++++++++++++++++--------------
> >  kernel/sched/core.c     |  41 +++----
> >  kernel/sched/deadline.c |  67 ++++++++---
> >  kernel/sched/sched.h    |   2 +-
> >  7 files changed, 244 insertions(+), 128 deletions(-)
> 
> Aside from a few niggles, these look fine to me. Who were you expecting
> to merge these, tj or me?

Thanks for reviewing!

Not entirely sure, it's kind of split, but maybe the cgroup changes are
predominant (cpuset_mutex is probably contributing the most). So, maybe
tj? Assuming this looks good to him as well of course. :)

Thanks!

Re: [PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

[Tejun Heo]

On Thu, May 04, 2023 at 10:17:41AM +0200, Juri Lelli wrote:
> On 04/05/23 08:25, Peter Zijlstra wrote:
> > On Wed, May 03, 2023 at 09:22:22AM +0200, Juri Lelli wrote:
> > 
> > > Dietmar Eggemann (2):
> > >   sched/deadline: Create DL BW alloc, free & check overflow interface
> > >   cgroup/cpuset: Free DL BW in case can_attach() fails
> > > 
> > > Juri Lelli (4):
> > >   cgroup/cpuset: Rename functions dealing with DEADLINE accounting
> > >   sched/cpuset: Bring back cpuset_mutex
> > >   sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets
> > >   cgroup/cpuset: Iterate only if DEADLINE tasks are present
> > > 
> > >  include/linux/cpuset.h  |  12 +-
> > >  include/linux/sched.h   |   4 +-
> > >  kernel/cgroup/cgroup.c  |   4 +
> > >  kernel/cgroup/cpuset.c  | 242 ++++++++++++++++++++++++++--------------
> > >  kernel/sched/core.c     |  41 +++----
> > >  kernel/sched/deadline.c |  67 ++++++++---
> > >  kernel/sched/sched.h    |   2 +-
> > >  7 files changed, 244 insertions(+), 128 deletions(-)
> > 
> > Aside from a few niggles, these look fine to me. Who were you expecting
> > to merge these, tj or me?
> 
> Thanks for reviewing!
> 
> Not entirely sure, it's kind of split, but maybe the cgroup changes are
> predominant (cpuset_mutex is probably contributing the most). So, maybe
> tj? Assuming this looks good to him as well of course. :)

Yeah, they all look sane to me and both Waiman and Peter seem okay with
them. If you post an updated version with the minor suggestions applied,
I'll route the series through the cgroup tree.

Thanks.

-- 
tejun

Re: [PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration

[Juri Lelli]

Hi,

On 05/05/23 09:31, Tejun Heo wrote:
> On Thu, May 04, 2023 at 10:17:41AM +0200, Juri Lelli wrote:
> > On 04/05/23 08:25, Peter Zijlstra wrote:
> > > On Wed, May 03, 2023 at 09:22:22AM +0200, Juri Lelli wrote:
> > > 
> > > > Dietmar Eggemann (2):
> > > >   sched/deadline: Create DL BW alloc, free & check overflow interface
> > > >   cgroup/cpuset: Free DL BW in case can_attach() fails
> > > > 
> > > > Juri Lelli (4):
> > > >   cgroup/cpuset: Rename functions dealing with DEADLINE accounting
> > > >   sched/cpuset: Bring back cpuset_mutex
> > > >   sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets
> > > >   cgroup/cpuset: Iterate only if DEADLINE tasks are present
> > > > 
> > > >  include/linux/cpuset.h  |  12 +-
> > > >  include/linux/sched.h   |   4 +-
> > > >  kernel/cgroup/cgroup.c  |   4 +
> > > >  kernel/cgroup/cpuset.c  | 242 ++++++++++++++++++++++++++--------------
> > > >  kernel/sched/core.c     |  41 +++----
> > > >  kernel/sched/deadline.c |  67 ++++++++---
> > > >  kernel/sched/sched.h    |   2 +-
> > > >  7 files changed, 244 insertions(+), 128 deletions(-)
> > > 
> > > Aside from a few niggles, these look fine to me. Who were you expecting
> > > to merge these, tj or me?
> > 
> > Thanks for reviewing!
> > 
> > Not entirely sure, it's kind of split, but maybe the cgroup changes are
> > predominant (cpuset_mutex is probably contributing the most). So, maybe
> > tj? Assuming this looks good to him as well of course. :)
> 
> Yeah, they all look sane to me and both Waiman and Peter seem okay with
> them. If you post an updated version with the minor suggestions applied,
> I'll route the series through the cgroup tree.

Thanks for reviewing and eventually taking care of the series. v3 just
posted (20230508075854.17215-1-juri.lelli@redhat.com).

Best,
Juri