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 404FFC433EF for ; Thu, 14 Jul 2022 12:33:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239291AbiGNMdu (ORCPT ); Thu, 14 Jul 2022 08:33:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51778 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231209AbiGNMdr (ORCPT ); Thu, 14 Jul 2022 08:33:47 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4677E2BDF for ; Thu, 14 Jul 2022 05:33:39 -0700 (PDT) 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 80CFA1CE2; Thu, 14 Jul 2022 05:33:39 -0700 (PDT) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D45E33F792; Thu, 14 Jul 2022 05:33:37 -0700 (PDT) Message-ID: <27f0675e-8ac3-2200-749f-7290a256e3d9@arm.com> Date: Thu, 14 Jul 2022 14:33:21 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH v2 09/10] sched/fair: stop load tracking when task switched_from_fair() Content-Language: en-US To: Chengming Zhou , mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, rostedt@goodmis.org, bsegall@google.com, vschneid@redhat.com Cc: linux-kernel@vger.kernel.org References: <20220713040430.25778-1-zhouchengming@bytedance.com> <20220713040430.25778-10-zhouchengming@bytedance.com> From: Dietmar Eggemann In-Reply-To: <20220713040430.25778-10-zhouchengming@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/07/2022 06:04, Chengming Zhou wrote: > The same reason as the previous commit, if we don't reset the > sched_avg last_update_time to 0, after a while in switched_to_fair(): > > switched_to_fair > attach_task_cfs_rq > attach_entity_cfs_rq > update_load_avg > __update_load_avg_se(now, cfs_rq, se) > > The delta (now - sa->last_update_time) will wrongly contribute/decay > sched_avg depends on the task running/runnable status at that time. IMHO, a queued !fair task when switching back to fair will already be enqueued (attached) as a fair task in __sched_setscheduler() prior to the check_class_changed() call. I can't see how this will work with your proposed change in using last_update_time=0 for fair->!fair->fair class changes? > This patch reset it's sched_avg last_update_time to 0, stop load > tracking for !fair task, later in switched_to_fair() -> > update_load_avg(), we can use its saved sched_avg. > > Signed-off-by: Chengming Zhou > --- > kernel/sched/fair.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 50f65a2ede32..576028f5a09e 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -11552,6 +11552,11 @@ static void attach_task_cfs_rq(struct task_struct *p) > static void switched_from_fair(struct rq *rq, struct task_struct *p) > { > detach_task_cfs_rq(p); > + > +#ifdef CONFIG_SMP > + /* Stop load tracking for !fair task */ > + p->se.avg.last_update_time = 0; > +#endif > } > > static void switched_to_fair(struct rq *rq, struct task_struct *p)