Commit 0d032a43 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

sched/mmcid: Prevent pointless work in mm_update_cpus_allowed() 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251119172549.385208276@linutronix.de
parent b08ef5fc

kernel/sched/core.c

+8 −3
Original line number Diff line number Diff line
@@ -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));

}