Commit cadefd3d authored Feb 27, 2014 by Peter Zijlstra Committed by Ingo Molnar Apr 18, 2014

sched: Make scale_rt_power() deal with backward clocks



Mike reported that, while unlikely, its entirely possible for
scale_rt_power() to see the time go backwards. This yields rather
'interesting' results.

So like all other sites that deal with clocks; make this one ignore
backward clock movement too.

Reported-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140227094035.GZ9987@twins.programming.kicks-ass.net


Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent a1d9a323

kernel/sched/fair.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -5564,6 +5564,7 @@ static unsigned long scale_rt_power(int cpu)
		{
		struct rq *rq = cpu_rq(cpu);
		u64 total, available, age_stamp, avg;
		s64 delta;

		/*
		* Since we're reading these variables without serialization make sure
		@@ -5572,7 +5573,11 @@ static unsigned long scale_rt_power(int cpu)
		age_stamp = ACCESS_ONCE(rq->age_stamp);
		avg = ACCESS_ONCE(rq->rt_avg);

		total = sched_avg_period() + (rq_clock(rq) - age_stamp);
		delta = rq_clock(rq) - age_stamp;
		if (unlikely(delta < 0))
		delta = 0;

		total = sched_avg_period() + delta;

		if (unlikely(total < avg)) {
		/* Ensures that power won't end up being negative */