From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6DBB9C61DF7 for ; Thu, 23 Nov 2023 13:13:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345399AbjKWNMd (ORCPT ); Thu, 23 Nov 2023 08:12:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345425AbjKWNM2 (ORCPT ); Thu, 23 Nov 2023 08:12:28 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 0FB83D64; Thu, 23 Nov 2023 05:12:31 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id F1C871042; Thu, 23 Nov 2023 05:13:16 -0800 (PST) Received: from [10.57.4.190] (unknown [10.57.4.190]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 25DA43F6C4; Thu, 23 Nov 2023 05:12:28 -0800 (PST) Message-ID: <3a381307-81a2-40ab-a2bf-f899e3fd7c80@arm.com> Date: Thu, 23 Nov 2023 13:13:27 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched/pelt: avoid underestimate of task utilization Content-Language: en-US To: Vincent Guittot References: <20231122140119.472110-1-vincent.guittot@linaro.org> Cc: mingo@redhat.com, peterz@infradead.org, rafael@kernel.org, qyousef@layalina.io, mgorman@suse.de, bsegall@google.com, rostedt@goodmis.org, linux-pm@vger.kernel.org, dietmar.eggemann@arm.com, juri.lelli@redhat.com, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, viresh.kumar@linaro.org From: Lukasz Luba In-Reply-To: <20231122140119.472110-1-vincent.guittot@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/22/23 14:01, Vincent Guittot wrote: > It has been reported that thread's util_est can significantly decrease as > a result of sharing the CPU with other threads. The use case can be easily > reproduced with a periodic task TA that runs 1ms and sleeps 100us. > When the task is alone on the CPU, its max utilization and its util_est is > around 888. If another similar task starts to run on the same CPU, TA will > have to share the CPU runtime and its maximum utilization will decrease > around half the CPU capacity (512) then TA's util_est will follow this new > maximum trend which is only the result of sharing the CPU with others > tasks. Such situation can be detected with runnable_avg wich is close or > equal to util_avg when TA is alone but increases above util_avg when TA > shares the CPU with other threads and wait on the runqueue. > > Signed-off-by: Vincent Guittot > --- > > This patch implements what I mentioned in [1]. I have been able to > reproduce such pattern with rt-app. > > [1] https://lore.kernel.org/lkml/CAKfTPtDd-HhF-YiNTtL9i5k0PfJbF819Yxu4YquzfXgwi7voyw@mail.gmail.com/#t Thanks Vincet for looking at it! I didn't have to to come back to this issue. > > kernel/sched/fair.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 07f555857698..eeb505d28905 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4774,6 +4774,11 @@ static inline unsigned long task_util(struct task_struct *p) > return READ_ONCE(p->se.avg.util_avg); > } > > +static inline unsigned long task_runnable(struct task_struct *p) > +{ > + return READ_ONCE(p->se.avg.runnable_avg); > +} > + > static inline unsigned long _task_util_est(struct task_struct *p) > { > struct util_est ue = READ_ONCE(p->se.avg.util_est); > @@ -4892,6 +4897,14 @@ static inline void util_est_update(struct cfs_rq *cfs_rq, > if (task_util(p) > arch_scale_cpu_capacity(cpu_of(rq_of(cfs_rq)))) > return; > > + /* > + * To avoid underestimate of task utilization, skip updates of ewma if > + * we cannot grant that thread got all CPU time it wanted. > + */ > + if ((ue.enqueued + UTIL_EST_MARGIN) < task_runnable(p)) > + goto done; > + > + > /* > * Update Task's estimated utilization > * That looks reasonable to do. I cannot test it right now on my pixel6. It should do the trick to the task util that we need in bigger apps than rt-app as well. Reviewed-by: Lukasz luba