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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 6D5A2C433E6 for ; Wed, 3 Feb 2021 15:20:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1616064F8C for ; Wed, 3 Feb 2021 15:20:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234430AbhBCPUs (ORCPT ); Wed, 3 Feb 2021 10:20:48 -0500 Received: from foss.arm.com ([217.140.110.172]:41994 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234283AbhBCPSI (ORCPT ); Wed, 3 Feb 2021 10:18:08 -0500 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 C399C12FC; Wed, 3 Feb 2021 07:17:22 -0800 (PST) Received: from e107158-lin (e107158-lin.cambridge.arm.com [10.1.194.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 71E3F3F73B; Wed, 3 Feb 2021 07:17:21 -0800 (PST) Date: Wed, 3 Feb 2021 15:17:18 +0000 From: Qais Yousef To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Morten Rasmussen , Quentin Perret , Pavan Kondeti , Rik van Riel Subject: Re: [PATCH 8/8] sched/fair: Relax task_hot() for misfit tasks Message-ID: <20210203151718.fg5idcfqbdqhkrah@e107158-lin> References: <20210128183141.28097-1-valentin.schneider@arm.com> <20210128183141.28097-9-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210128183141.28097-9-valentin.schneider@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/28/21 18:31, Valentin Schneider wrote: > Misfit tasks can and will be preempted by the stopper to migrate them over > to a higher-capacity CPU. However, when runnable but not current misfit > tasks are scanned by the load balancer (i.e. detach_tasks()), the > task_hot() ratelimiting logic may prevent us from enqueuing said task onto > a higher-capacity CPU. > > Align detach_tasks() with the active-balance logic and let it pick a > cache-hot misfit task when the destination CPU can provide a capacity > uplift. Good catch. > > Signed-off-by: Valentin Schneider > --- > kernel/sched/fair.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index cba9f97d9beb..c2351b87824f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -7484,6 +7484,17 @@ static int task_hot(struct task_struct *p, struct lb_env *env) > if (env->sd->flags & SD_SHARE_CPUCAPACITY) > return 0; > > + /* > + * On a (sane) asymmetric CPU capacity system, the increase in compute > + * capacity should offset any potential performance hit caused by a > + * migration. > + */ > + if (sd_has_asym_cpucapacity(env->sd) && > + env->idle != CPU_NOT_IDLE && > + !task_fits_capacity(p, capacity_of(env->src_cpu)) && Note for a very busy task that is running on the biggest cpu this will always return true. > + cpu_capacity_greater(env->dst_cpu, env->src_cpu)) But this will save us from triggering unnecessary migration. We could swap them and optimize for this particular case, but tbh this is the type of micro optimization that is hard to know whether it makes a real difference or not.. Anyways, this looks good to me. Reviewed-by: Qais Yousef Thanks -- Qais Yousef > + return 0; > + > /* > * Buddy candidates are cache hot: > */ > -- > 2.27.0 >