From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S968150AbdDSRLR (ORCPT ); Wed, 19 Apr 2017 13:11:17 -0400 Received: from mail-wr0-f170.google.com ([209.85.128.170]:34789 "EHLO mail-wr0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966619AbdDSQpX (ORCPT ); Wed, 19 Apr 2017 12:45:23 -0400 From: Vincent Guittot To: peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org Cc: dietmar.eggemann@arm.com, Morten.Rasmussen@arm.com, yuyang.du@intel.com, pjt@google.com, bsegall@google.com, Vincent Guittot Subject: [PATCH 1/2] sched/cfs: make util/load_avg more stable Date: Wed, 19 Apr 2017 18:44:16 +0200 Message-Id: <1492620257-30109-2-git-send-email-vincent.guittot@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1492620257-30109-1-git-send-email-vincent.guittot@linaro.org> References: <1492619370-29246-1-git-send-email-vincent.guittot@linaro.org> <1492620257-30109-1-git-send-email-vincent.guittot@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Signed-off-by: Vincent Guittot --- 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