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sched/mmcid: Prevent pointless work in mm_update_cpus_allowed()

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mm_update_cpus_allowed() is not required to be invoked for affinity changes
due to migrate_disable() and migrate_enable().

migrate_disable() restricts the task temporarily to a CPU on which the task
was already allowed to run, so nothing changes. migrate_enable() restores
the actual task affinity mask.

If that mask changed between migrate_disable() and migrate_enable() then
that change was already accounted for.

Move the invocation to the proper place to avoid that.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251119172549.385208276@linutronix.de
This commit is contained in:
Thomas Gleixner
2025-11-19 18:26:55 +01:00
committed by Peter Zijlstra
parent b08ef5fc8f
commit 0d032a43eb
1 changed files with 8 additions and 3 deletions
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11
kernel/sched/core.c
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@@ -2684,6 +2684,7 @@ void set_cpus_allowed_common(struct task_struct *p, struct affinity_context *ctx
cpumask_copy(&p->cpus_mask, ctx->new_mask);
p->nr_cpus_allowed = cpumask_weight(ctx->new_mask);
mm_update_cpus_allowed(p->mm, ctx->new_mask);
/*
* Swap in a new user_cpus_ptr if SCA_USER flag set
@@ -2730,7 +2731,6 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
put_prev_task(rq, p);
p->sched_class->set_cpus_allowed(p, ctx);
mm_update_cpus_allowed(p->mm, ctx->new_mask);
if (queued)
enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
@@ -10376,12 +10376,17 @@ void call_trace_sched_update_nr_running(struct rq *rq, int count)
*/
static inline void mm_update_cpus_allowed(struct mm_struct *mm, const struct cpumask *affmsk)
{
struct cpumask *mm_allowed = mm_cpus_allowed(mm);
struct cpumask *mm_allowed;
if (!mm)
return;
/* The mm_cpus_allowed is the union of each thread allowed CPUs masks. */
/*
* mm::mm_cid::mm_cpus_allowed is the superset of each threads
* allowed CPUs mask which means it can only grow.
*/
guard(raw_spinlock)(&mm->mm_cid.lock);
mm_allowed = mm_cpus_allowed(mm);
cpumask_or(mm_allowed, mm_allowed, affmsk);
WRITE_ONCE(mm->mm_cid.nr_cpus_allowed, cpumask_weight(mm_allowed));
}