Commit f01114cb authored May 31, 2011 by Peter Zijlstra Committed by Ingo Molnar May 31, 2011

sched: Fix cross-cpu clock sync on remote wakeups



Markus reported that commit 317f3941 ("sched: Move the second half
of ttwu() to the remote cpu") caused some accounting funnies on his AMD
Phenom II X4, such as weird 'top' results.

It turns out that this is due to non-synced TSC and the queued remote
wakeups stopped coupeling the two relevant cpu clocks, which leads to
wakeups seeing time jumps, which in turn lead to skewed runtime stats.

Add an explicit call to sched_clock_cpu() to couple the per-cpu clocks
to restore the normal flow of time.

Reported-and-tested-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1306835745.2353.3.camel@twins


Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 1e1b6c51

kernel/sched.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -2600,6 +2600,7 @@ static void ttwu_queue(struct task_struct *p, int cpu)

		#if defined(CONFIG_SMP)
		if (sched_feat(TTWU_QUEUE) && cpu != smp_processor_id()) {
		sched_clock_cpu(cpu); /* sync clocks x-cpu */
		ttwu_queue_remote(p, cpu);
		return;
		}

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