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Commit a15b12ac authored by Kirill Tkhai's avatar Kirill Tkhai Committed by Ingo Molnar
Browse files

sched: Do not stop cpu in set_cpus_allowed_ptr() if task is not running 



If a task is queued but not running on it rq, we can simply migrate
it without migration thread and switching of context.

Signed-off-by: default avatarKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1410519814.3569.7.camel@tkhai


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1ba93d42

kernel/sched/core.c

+32 −15
Original line number Diff line number Diff line
@@ -4629,6 +4629,33 @@ void init_idle(struct task_struct *idle, int cpu) 
}



#ifdef CONFIG_SMP

/*

 * move_queued_task - move a queued task to new rq.

 *

 * Returns (locked) new rq. Old rq's lock is released.

 */

static struct rq *move_queued_task(struct task_struct *p, int new_cpu)

{

	struct rq *rq = task_rq(p);



	lockdep_assert_held(&rq->lock);



	dequeue_task(rq, p, 0);

	p->on_rq = TASK_ON_RQ_MIGRATING;

	set_task_cpu(p, new_cpu);

	raw_spin_unlock(&rq->lock);



	rq = cpu_rq(new_cpu);



	raw_spin_lock(&rq->lock);

	BUG_ON(task_cpu(p) != new_cpu);

	p->on_rq = TASK_ON_RQ_QUEUED;

	enqueue_task(rq, p, 0);

	check_preempt_curr(rq, p, 0);



	return rq;

}



void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)

{

	if (p->sched_class && p->sched_class->set_cpus_allowed)
@@ -4685,14 +4712,15 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask) 
		goto out;



	dest_cpu = cpumask_any_and(cpu_active_mask, new_mask);

	if (task_on_rq_queued(p) || p->state == TASK_WAKING) {

	if (task_running(rq, p) || p->state == TASK_WAKING) {

		struct migration_arg arg = { p, dest_cpu };

		/* Need help from migration thread: drop lock and wait. */

		task_rq_unlock(rq, p, &flags);

		stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);

		tlb_migrate_finish(p->mm);

		return 0;

	}

	} else if (task_on_rq_queued(p))

		rq = move_queued_task(p, dest_cpu);

out:

	task_rq_unlock(rq, p, &flags);
@@ -4735,19 +4763,8 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) 
	 * If we're not on a rq, the next wake-up will ensure we're

	 * placed properly.

	 */

	if (task_on_rq_queued(p)) {

		dequeue_task(rq, p, 0);

		p->on_rq = TASK_ON_RQ_MIGRATING;

		set_task_cpu(p, dest_cpu);

		raw_spin_unlock(&rq->lock);



		rq = cpu_rq(dest_cpu);

		raw_spin_lock(&rq->lock);

		BUG_ON(task_rq(p) != rq);

		p->on_rq = TASK_ON_RQ_QUEUED;

		enqueue_task(rq, p, 0);

		check_preempt_curr(rq, p, 0);

	}

	if (task_on_rq_queued(p))

		rq = move_queued_task(p, dest_cpu);

done:

	ret = 1;

fail: