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Date: Wed, 19 Apr 2017 18:44:16 +0200 From: Vincent Guittot <vincent.guittot@...aro.org> To: peterz@...radead.org, mingo@...nel.org, linux-kernel@...r.kernel.org Cc: dietmar.eggemann@....com, Morten.Rasmussen@....com, yuyang.du@...el.com, pjt@...gle.com, bsegall@...gle.com, Vincent Guittot <vincent.guittot@...aro.org> Subject: [PATCH 1/2] sched/cfs: make util/load_avg more stable In the current implementation of load/util_avg, we assume that the ongoing time segment has fully elapsed, and util/load_sum is divided by LOAD_AVG_MAX, even if part of the time segment still remains. As a consequence, this remaining part is considered as idle time and generates unexpected variations of util_avg of a busy CPU in the range ]1002..1024[ whereas util_avg should stay at 1023. In order to keep the metric stable, we should not consider the ongoing time segment when computing load/util_avg but only the segments that have already fully elapsed. Suggested-by: Peter Zijlstra <peterz@...radead.org> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org> --- Sorry some unexpected characters appeared in the commit message of previous version kernel/sched/fair.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3f83a35..f74da94 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3017,12 +3017,15 @@ ___update_load_avg(u64 now, int cpu, struct sched_avg *sa, /* * Step 2: update *_avg. */ - sa->load_avg = div_u64(sa->load_sum, LOAD_AVG_MAX); + sa->load_avg = div_u64((sa->load_sum - sa->period_contrib * weight), + (LOAD_AVG_MAX - 1024)); if (cfs_rq) { cfs_rq->runnable_load_avg = - div_u64(cfs_rq->runnable_load_sum, LOAD_AVG_MAX); + div_u64((cfs_rq->runnable_load_sum - sa->period_contrib * weight), + (LOAD_AVG_MAX - 1024)); } - sa->util_avg = sa->util_sum / LOAD_AVG_MAX; + sa->util_avg = (sa->util_sum - (running * sa->period_contrib << SCHED_CAPACITY_SHIFT)) / + (LOAD_AVG_MAX - 1024); return 1; } -- 2.7.4
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