Commit bb0bd044 authored Apr 10, 2017 by Peter Zijlstra Committed by Ingo Molnar Apr 14, 2017

sched/fair: Increase PELT accuracy for small tasks



We truncate (and loose) the lower 10 bits of runtime in
___update_load_avg(), this means there's a consistent bias to
under-account tasks. This is esp. significant for small tasks.

Cure this by only forwarding last_update_time to the point we've
actually accounted for, leaving the remainder for the next time.

Reported-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 3841cdc3

kernel/sched/fair.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -2915,7 +2915,8 @@ ___update_load_avg(u64 now, int cpu, struct sched_avg *sa,
		delta >>= 10;
		if (!delta)
		return 0;
		sa->last_update_time = now;

		sa->last_update_time += delta << 10;

		/*
		* Now we know we crossed measurement unit boundaries. The *_avg

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