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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>
This commit is contained in:
Peter Zijlstra 2014-02-27 10:40:35 +01:00 committed by Ingo Molnar
parent a1d9a3231e
commit cadefd3d6c
1 changed files with 6 additions and 1 deletions
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7
kernel/sched/fair.c
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@ -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 */