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 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 CE44EC4332E for ; Tue, 19 Jan 2021 12:35:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 89DFF22E00 for ; Tue, 19 Jan 2021 12:35:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393093AbhASMce (ORCPT ); Tue, 19 Jan 2021 07:32:34 -0500 Received: from foss.arm.com ([217.140.110.172]:54870 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404319AbhASMZa (ORCPT ); Tue, 19 Jan 2021 07:25:30 -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 31A2A1396; Tue, 19 Jan 2021 04:24:44 -0800 (PST) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 322033F719; Tue, 19 Jan 2021 04:24:43 -0800 (PST) From: Valentin Schneider To: Qais Yousef , "Peter Zijlstra \(Intel\)" , Dietmar Eggemann , Vincent Guittot Cc: linux-kernel@vger.kernel.org, Morten Rasmussen , Qais Yousef Subject: Re: [PATCH] sched/eas: Don't update misfit status if the task is pinned In-Reply-To: <20210119120755.2425264-1-qais.yousef@arm.com> References: <20210119120755.2425264-1-qais.yousef@arm.com> User-Agent: Notmuch/0.21 (http://notmuchmail.org) Emacs/26.3 (x86_64-pc-linux-gnu) Date: Tue, 19 Jan 2021 12:24:38 +0000 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Nit: Topic should probably be sched/fair - not many other than us loonies talk about EAS, and misfit stuff doesn't require an energy model, only CPU capacity asymmetry. On 19/01/21 12:07, Qais Yousef wrote: > If the task is pinned to a cpu, setting the misfit status means that > we'll unnecessarily continuously attempt to migrate the task but fail. > > This continuous failure will cause the balance_interval to increase to > a high value, and eventually cause unnecessary significant delays in > balancing the system when real imbalance happens. > > Caught while testing uclamp where rt-app calibration loop was pinned to > cpu 0, shortly after which we spawn another task with high util_clamp > value. The task was failing to migrate after over 40ms of runtime due to > balance_interval unnecessary expanded to a very high value from the > calibration loop. > > Not done here, but it could be useful to extend the check for pinning to > verify that the affinity of the task has a cpu that fits. We could end > up in a similar situation otherwise. > > Fixes: 3b1baa6496e6 ("sched/fair: Add 'group_misfit_task' load-balance type") > Signed-off-by: Qais Yousef Acked-by: Valentin Schneider Thanks! > --- > kernel/sched/fair.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 197a51473e0c..9379a481dd8c 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4060,7 +4060,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq) > if (!static_branch_unlikely(&sched_asym_cpucapacity)) > return; > > - if (!p) { > + if (!p || p->nr_cpus_allowed == 1) { > rq->misfit_task_load = 0; > return; > } > -- > 2.25.1