sched: Update the clock of runqueue select_task_rq() selected (f5dc3753) · Commits · 戴 / test

In try_to_wake_up(), we update the runqueue clock, but select_task_rq() may select a different runqueue than the one we updated, leaving the new runqueue's clock stale for a bit. This patch cures occasional huge latencies reported by latencytop when coming out of idle on a mostly idle NO_HZ box. Signed-off-by:

Mike Galbraith <efault@gmx.de> Signed-off-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1255070103.7639.30.camel@marge.simson.net> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/sched.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -2311,7 +2311,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
		{
		int cpu, orig_cpu, this_cpu, success = 0;
		unsigned long flags;
		struct rq *rq;
		struct rq rq, orig_rq;

		if (!sched_feat(SYNC_WAKEUPS))
		wake_flags &= ~WF_SYNC;
		@@ -2319,7 +2319,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
		this_cpu = get_cpu();

		smp_wmb();
		rq = task_rq_lock(p, &flags);
		rq = orig_rq = task_rq_lock(p, &flags);
		update_rq_clock(rq);
		if (!(p->state & state))
		goto out;
		@@ -2350,6 +2350,10 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
		set_task_cpu(p, cpu);

		rq = task_rq_lock(p, &flags);

		if (rq != orig_rq)
		update_rq_clock(rq);

		WARN_ON(p->state != TASK_WAKING);
		cpu = task_cpu(p);

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