From bb0bd044e65c2bf0f26b29613fcc441dfdeedf14 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 10 Apr 2017 13:20:45 +0200 Subject: 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 Signed-off-by: Peter Zijlstra (Intel) Acked-by: Morten Rasmussen Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/sched/fair.c') diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d43e9ac9c3c5..1e3b99a9ab69 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -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 -- cgit v1.2.3-55-g7522