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 6D5E0C433EF for ; Fri, 15 Jul 2022 05:08:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229498AbiGOFId (ORCPT ); Fri, 15 Jul 2022 01:08:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229441AbiGOFI3 (ORCPT ); Fri, 15 Jul 2022 01:08:29 -0400 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2EC2178DE9 for ; Thu, 14 Jul 2022 22:08:28 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=cruzzhao@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0VJNsa4y_1657861703; Received: from 30.97.49.8(mailfrom:cruzzhao@linux.alibaba.com fp:SMTPD_---0VJNsa4y_1657861703) by smtp.aliyun-inc.com; Fri, 15 Jul 2022 13:08:24 +0800 Message-ID: <4107a52c-131e-d683-898d-cdd2c2448137@linux.alibaba.com> Date: Fri, 15 Jul 2022 13:08:23 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH 1/3] sched/core: Fix the bug that task won't enqueue into core tree when update cookie Content-Language: en-US To: Peter Zijlstra Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org References: <1656403045-100840-1-git-send-email-CruzZhao@linux.alibaba.com> <1656403045-100840-2-git-send-email-CruzZhao@linux.alibaba.com> From: cruzzhao In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022/7/4 下午4:53, Peter Zijlstra 写道: > Subject: sched/core: Fix the bug that task won't enqueue into core tree when update cookie > From: Cruz Zhao > Date: Tue, 28 Jun 2022 15:57:23 +0800 > > From: Cruz Zhao > > In function sched_core_update_cookie(), a task will enqueue into the > core tree only when it enqueued before, that is, if an uncookied task > is cookied, it will not enqueue into the core tree until it enqueue > again, which will result in unnecessary force idle. > > Here follows the scenario: > CPU x and CPU y are a pair of SMT siblings. > 1. Start task a running on CPU x without sleeping, and task b and > task c running on CPU y without sleeping. > 2. We create a cookie and share it to task a and task b, and then > we create another cookie and share it to task c. > 3. Simpling core_forceidle_sum of task a and b from /proc/PID/sched > > And we will find out that core_forceidle_sum of task a takes 30% > time of the sampling period, which shouldn't happen as task a and b > have the same cookie. > > Then we migrate task a to CPU x', migrate task b and c to CPU y', where > CPU x' and CPU y' are a pair of SMT siblings, and sampling again, we > will found out that core_forceidle_sum of task a and b are almost zero. > > To solve this problem, we enqueue the task into the core tree if it's > on rq. > > Fixes: 6e33cad0af49("sched: Trivial core scheduling cookie management") > Signed-off-by: Cruz Zhao > Signed-off-by: Peter Zijlstra (Intel) > Link: https://lkml.kernel.org/r/1656403045-100840-2-git-send-email-CruzZhao@linux.alibaba.com > --- > kernel/sched/core_sched.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > --- a/kernel/sched/core_sched.c > +++ b/kernel/sched/core_sched.c > @@ -56,7 +56,6 @@ static unsigned long sched_core_update_c > unsigned long old_cookie; > struct rq_flags rf; > struct rq *rq; > - bool enqueued; > > rq = task_rq_lock(p, &rf); > > @@ -68,14 +67,16 @@ static unsigned long sched_core_update_c > */ > SCHED_WARN_ON((p->core_cookie || cookie) && !sched_core_enabled(rq)); > > - enqueued = sched_core_enqueued(p); > - if (enqueued) > + if (sched_core_enqueued(p)) > sched_core_dequeue(rq, p, DEQUEUE_SAVE); > > old_cookie = p->core_cookie; > p->core_cookie = cookie; > > - if (enqueued) > + /* > + * Consider the cases: !prev_cookie and !cookie. > + */ > + if (cookie && task_on_rq_queued(p)) > sched_core_enqueue(rq, p); > > /* LGTM.