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,URIBL_BLOCKED,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 F0CF9C433E6 for ; Fri, 19 Feb 2021 13:05:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAF2164EC7 for ; Fri, 19 Feb 2021 13:05:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230283AbhBSNFh (ORCPT ); Fri, 19 Feb 2021 08:05:37 -0500 Received: from foss.arm.com ([217.140.110.172]:35956 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230235AbhBSNEH (ORCPT ); Fri, 19 Feb 2021 08:04:07 -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 494421435; Fri, 19 Feb 2021 05:02:43 -0800 (PST) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id B6B963F73B; Fri, 19 Feb 2021 05:02:41 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Qais Yousef , Peter Zijlstra , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Morten Rasmussen , Quentin Perret , Pavan Kondeti , Rik van Riel , Lingutla Chandrasekhar Subject: [PATCH v2 7/7] sched/fair: Relax task_hot() for misfit tasks Date: Fri, 19 Feb 2021 13:00:03 +0000 Message-Id: <20210219130003.2890-8-valentin.schneider@arm.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210219130003.2890-1-valentin.schneider@arm.com> References: <20210219130003.2890-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Consider the following topology: DIE [ ] MC [ ][ ] 0 1 2 3 capacity_orig_of(x \in {0-1}) < capacity_orig_of(x \in {2-3}) w/ CPUs 2-3 idle and CPUs 0-1 running CPU hogs (util_avg=1024). When CPU2 goes through load_balance() (via periodic / NOHZ balance), it should pull one CPU hog from either CPU0 or CPU1 (this is misfit task upmigration). However, should a e.g. pcpu kworker awake on CPU0 just before this load_balance() happens and preempt the CPU hog running there, we would have, for the [0-1] group at CPU2's DIE level: o sgs->sum_nr_running > sgs->group_weight o sgs->group_capacity * 100 < sgs->group_util * imbalance_pct IOW, this group is group_overloaded. Considering CPU0 is picked by find_busiest_queue(), we would then visit the preempted CPU hog in detach_tasks(). However, given it has just been preempted by this pcpu kworker, task_hot() will prevent it from being detached. We then leave load_balance() without having done anything. Long story short, preempted misfit tasks are affected by task_hot(), while currently running misfit tasks are intentionally preempted by the stopper task to migrate them over to 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. Reviewed-by: Qais Yousef 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 ee172b384e29..554430fd249c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7448,6 +7448,17 @@ 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)) && + cpu_capacity_greater(env->dst_cpu, env->src_cpu)) + return 0; + /* * Buddy candidates are cache hot: */ -- 2.27.0