stop_machine: Avoid a sleep and wakeup in stop_one_cpu() (bf89a304) · Commits · 戴 / test

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:

Cheng Chao <cs.os.kernel@gmail.com> Signed-off-by:

Peter 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:

Ingo Molnar <mingo@kernel.org>

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;
		}

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