Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit bf89a304 authored by Cheng Chao's avatar Cheng Chao Committed by Ingo Molnar
Browse files

stop_machine: Avoid a sleep and wakeup in stop_one_cpu() 



In case @cpu == smp_proccessor_id(), we can avoid a sleep+wakeup
cycle by doing a preemption.

Callers such as sched_exec() can benefit from this change.

Signed-off-by: default avatarCheng Chao <cs.os.kernel@gmail.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: chris@chris-wilson.co.uk
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/1473818510-6779-1-git-send-email-cs.os.kernel@gmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 0b847357

kernel/sched/core.c

+6 −2
Original line number Diff line number Diff line
@@ -1063,8 +1063,12 @@ static int migration_cpu_stop(void *data) 
	 * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because

	 * we're holding p->pi_lock.

	 */

	if (task_rq(p) == rq && task_on_rq_queued(p))

	if (task_rq(p) == rq) {

		if (task_on_rq_queued(p))

			rq = __migrate_task(rq, p, arg->dest_cpu);

		else

			p->wake_cpu = arg->dest_cpu;

	}

	raw_spin_unlock(&rq->lock);

	raw_spin_unlock(&p->pi_lock);

kernel/stop_machine.c

+5 −0
Original line number Diff line number Diff line
@@ -126,6 +126,11 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) 
	cpu_stop_init_done(&done, 1);

	if (!cpu_stop_queue_work(cpu, &work))

		return -ENOENT;

	/*

	 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup

	 * cycle by doing a preemption:

	 */

	cond_resched();

	wait_for_completion(&done.completion);

	return done.ret;

}