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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3602AC433FF for ; Fri, 2 Aug 2019 14:27:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F94A20679 for ; Fri, 2 Aug 2019 14:27:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394887AbfHBO1W (ORCPT ); Fri, 2 Aug 2019 10:27:22 -0400 Received: from foss.arm.com ([217.140.110.172]:52790 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726667AbfHBO1V (ORCPT ); Fri, 2 Aug 2019 10:27:21 -0400 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 1D47C1570; Fri, 2 Aug 2019 07:27:21 -0700 (PDT) Received: from [10.1.194.37] (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CC2593F575; Fri, 2 Aug 2019 07:27:19 -0700 (PDT) Subject: Re: [PATCH v3] sched/fair: use utilization to select misfit task To: Vincent Guittot , linux-kernel@vger.kernel.org, mingo@redhat.com, peterz@infradead.org Cc: pauld@redhat.com, srikar@linux.vnet.ibm.com, quentin.perret@arm.com, dietmar.eggemann@arm.com, Morten.Rasmussen@arm.com, Thomas Gleixner References: <1564670424-26023-9-git-send-email-vincent.guittot@linaro.org> <1564750572-20251-1-git-send-email-vincent.guittot@linaro.org> From: Valentin Schneider Message-ID: Date: Fri, 2 Aug 2019 15:27:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <1564750572-20251-1-git-send-email-vincent.guittot@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/08/2019 13:56, Vincent Guittot wrote: > utilization is used to detect a misfit task but the load is then used to > select the task on the CPU which can lead to select a small task with > high weight instead of the task that triggered the misfit migration. > > Signed-off-by: Vincent Guittot > --- > Keep tracking load instead of utilization but check that > task doesn't fit CPU's capacity when selecting the task to detach as > suggested by Valentin > I find that one much better :) The very same fix could be applied regardless of the rework, so FWIW (providing the changelog gets a bit clearer - maybe squash the comment in it): Acked-by: Valentin Schneider One more thing though: we actually face the same problem in active balance, i.e. the misfit task could sleep/get preempted before the CPU stopper actually runs, and that latter would migrate $random. I was thinking of passing the lb_env to stop_one_cpu_nowait() - we'd have to rebuild it in active_load_balance_cpu_stop() anyway, but we could copy things like env.migration_type so that we remember that we should be picking a misfit task and have a similar detach guard. Sadly, the lb_env struct is on load_balance()'s stack, and that's a nowait call :/ Peter/Thomas, would there be much hate in adding some sort of flags field to struct cpu_stop_work? Or if you see a better alternative, I'm all ears. > kernel/sched/fair.c | 12 +++--------- > 1 file changed, 3 insertions(+), 9 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 53e64a7..8496118 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -7487,15 +7487,9 @@ static int detach_tasks(struct lb_env *env) > break; > > case migrate_misfit: > - load = task_h_load(p); > - > - /* > - * utilization of misfit task might decrease a bit > - * since it has been recorded. Be conservative in the > - * condition. > - */ > - if (load < env->imbalance) > - goto next; > + /* This is not a misfit task */ > + if (task_fits_capacity(p, capacity_of(env->src_cpu))) > + goto next; > > env->imbalance = 0; > break; >