[PATCH v9 08/20] cpuset: Cleanup cpuset_cpus_allowed_fallback() use in select_fallback_rq()

Will Deacon
2021-06-08T18:04:05Z

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>
---
include/linux/cpuset.h | 5 +++--
kernel/cgroup/cpuset.c | 10 ++++++++--
kernel/sched/core.c | 3 +--
3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 414a8e694413..d2b9c41c8edf 100644
--- 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 4e7c271e3800..a6bab2259f98 100644
--- 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 *cs_mask;
+ bool changed = false;
const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);

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 0c1b6f1a6c91..9e75cb3fbc9c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2779,8 +2779,7 @@ 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;
}
--
2.32.0.rc1.229.g3e70b5a671-goog