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 0CA25C433E0 for ; Tue, 19 Jan 2021 08:37:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BAE9523134 for ; Tue, 19 Jan 2021 08:37:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731381AbhASIhI (ORCPT ); Tue, 19 Jan 2021 03:37:08 -0500 Received: from foss.arm.com ([217.140.110.172]:44504 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731279AbhASIgr (ORCPT ); Tue, 19 Jan 2021 03:36:47 -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 57C5031B; Tue, 19 Jan 2021 00:35:55 -0800 (PST) Received: from e125579.fritz.box (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 67B5D3F66E; Tue, 19 Jan 2021 00:35:53 -0800 (PST) From: Dietmar Eggemann To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Daniel Bristot de Oliveira Cc: linux-kernel@vger.kernel.org, Vincent Guittot , Steven Rostedt , Quentin Perret , Valentin Schneider Subject: [PATCH] sched/deadline: Reduce rq lock contention in dl_add_task_root_domain() Date: Tue, 19 Jan 2021 09:35:42 +0100 Message-Id: <20210119083542.19856-1-dietmar.eggemann@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 dl_add_task_root_domain() is called during sched domain rebuild: rebuild_sched_domains_locked() partition_and_rebuild_sched_domains() rebuild_root_domains() for all top_cpuset descendants: update_tasks_root_domain() for all tasks of cpuset: dl_add_task_root_domain() Change it so that only the task pi lock is taken to check if the task has a SCHED_DEADLINE (DL) policy. In case that p is a DL task take the rq lock as well to be able to safely de-reference root domain's DL bandwidth structure. Most of the tasks will have another policy (namely SCHED_NORMAL) and can now bail without taking the rq lock. One thing to note here: Even in case that there aren't any DL user tasks, a slow frequency switching system with cpufreq gov schedutil has a DL task (sugov) per frequency domain running which participates in DL bandwidth management. Reviewed-by: Quentin Perret Signed-off-by: Dietmar Eggemann --- The use case in which this makes a noticeable difference is Android's 'CPU pause' power management feature. It uses CPU hotplug control to clear a CPU from active state to force all threads which are not per-cpu kthreads away from this CPU. Making DL bandwidth management faster during sched domain rebuild helps to reduce the time to pause/un-pause a CPU. kernel/sched/deadline.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 5421782fe897..c7b1a63a053b 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2409,9 +2409,13 @@ void dl_add_task_root_domain(struct task_struct *p) struct rq *rq; struct dl_bw *dl_b; - rq = task_rq_lock(p, &rf); - if (!dl_task(p)) - goto unlock; + raw_spin_lock_irqsave(&p->pi_lock, rf.flags); + if (!dl_task(p)) { + raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags); + return; + } + + rq = __task_rq_lock(p, &rf); dl_b = &rq->rd->dl_bw; raw_spin_lock(&dl_b->lock); @@ -2420,7 +2424,6 @@ void dl_add_task_root_domain(struct task_struct *p) raw_spin_unlock(&dl_b->lock); -unlock: task_rq_unlock(rq, p, &rf); } -- 2.25.1