cpuset: Cleanup cpuset_cpus_allowed_fallback() use in select_fallback_rq()

select_fallback_rq() only needs to recheck for an allowed CPU if the
affinity mask of the task has changed since the last check.

Return a 'bool' from cpuset_cpus_allowed_fallback() to indicate whether
the affinity mask was updated, and use this to elide the allowed check
when the mask has been left alone.

No functional change.

Suggested-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lore.kernel.org/r/20210730112443.23245-5-will@kernel.org

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 414a8e694413ec286dc76021e7788bfb2d5d39db..d2b9c41c8edf5e8f552cf0fee5fe5bb9414fb090 100644 (file)
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -59,7 +59,7 @@ extern void cpuset_wait_for_hotplug(void);
 extern void cpuset_read_lock(void);
 extern void cpuset_read_unlock(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
-extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
+extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
@@ -188,8 +188,9 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,
        cpumask_copy(mask, task_cpu_possible_mask(p));
 }
 
-static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
+static inline bool cpuset_cpus_allowed_fallback(struct task_struct *p)
 {
+       return false;
 }
 
 static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 391813245cb25d83ef8a3a2fd4f82f1a2e117630..6500cbe0ce16ef75b36dcee6897e7e6474de07ab 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3327,17 +3327,22 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
  * which will not contain a sane cpumask during cases such as cpu hotplugging.
  * This is the absolute last resort for the scheduler and it is only used if
  * _every_ other avenue has been traveled.
+ *
+ * Returns true if the affinity of @tsk was changed, false otherwise.
  **/
 
-void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
+bool cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
        const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
        const struct cpumask *cs_mask;
+       bool changed = false;
 
        rcu_read_lock();
        cs_mask = task_cs(tsk)->cpus_allowed;
-       if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask))
+       if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask)) {
                do_set_cpus_allowed(tsk, cs_mask);
+               changed = true;
+       }
        rcu_read_unlock();
 
        /*
@@ -3357,6 +3362,7 @@ void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
         * select_fallback_rq() will fix things ups and set cpu_possible_mask
         * if required.
         */
+       return changed;
 }
 
 void __init cpuset_init_current_mems_allowed(void)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6f31267c4bebed480273ca48062f9b54689b5b5b..b9d4bae922a8e9887f8f7f5140a6f639d64a2bba 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3141,8 +3141,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
                /* No more Mr. Nice Guy. */
                switch (state) {
                case cpuset:
-                       if (IS_ENABLED(CONFIG_CPUSETS)) {
-                               cpuset_cpus_allowed_fallback(p);
+                       if (cpuset_cpus_allowed_fallback(p)) {
                                state = possible;
                                break;
                        }