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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 B10E2C433E0 for ; Tue, 19 Jan 2021 12:21:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7F1AF23104 for ; Tue, 19 Jan 2021 12:21:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392600AbhASMRX (ORCPT ); Tue, 19 Jan 2021 07:17:23 -0500 Received: from foss.arm.com ([217.140.110.172]:53906 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389776AbhASMI7 (ORCPT ); Tue, 19 Jan 2021 07:08:59 -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 14E96113E; Tue, 19 Jan 2021 04:08:13 -0800 (PST) Received: from e107158-lin.cambridge.arm.com (unknown [10.1.194.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 148A13F719; Tue, 19 Jan 2021 04:08:11 -0800 (PST) From: Qais Yousef To: "Peter Zijlstra (Intel)" , Dietmar Eggemann , Vincent Guittot Cc: linux-kernel@vger.kernel.org, Valentin Schneider , Morten Rasmussen , Qais Yousef Subject: [PATCH] sched/eas: Don't update misfit status if the task is pinned Date: Tue, 19 Jan 2021 12:07:55 +0000 Message-Id: <20210119120755.2425264-1-qais.yousef@arm.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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