From patchwork Mon Jul 12 06:06:33 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 475772 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=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 4C5CCC11F6A for ; Mon, 12 Jul 2021 07:10:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A549613C9 for ; Mon, 12 Jul 2021 07:10:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238818AbhGLHNo (ORCPT ); Mon, 12 Jul 2021 03:13:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:46854 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245383AbhGLHMR (ORCPT ); Mon, 12 Jul 2021 03:12:17 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CE2EC60C40; Mon, 12 Jul 2021 07:09:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626073768; bh=ZEf5bbSSXo3CDVXgfzGXaIxQqQTFuxtf50ZzYxxmL6c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oGZ5zQmiJ4sVarWUonuWVndiIvY50yUMdjTY+HtxGEE2C0pBwW0n9joiYDgmuofJs uC6lCcqurYaeIPxOx0T8D6eBGqC0B/rSRz9WHBg5yk4830Z84DpWCFdcfqJpsh/OBS ELwbDJ70AH32JJx3HSWXT2KlFOKKUFlpM4a/FkmY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vincent Donnefort , "Peter Zijlstra (Intel)" , Vincent Guittot , Sasha Levin Subject: [PATCH 5.12 310/700] sched/rt: Fix RT utilization tracking during policy change Date: Mon, 12 Jul 2021 08:06:33 +0200 Message-Id: <20210712061009.353140419@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210712060924.797321836@linuxfoundation.org> References: <20210712060924.797321836@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Vincent Donnefort [ Upstream commit fecfcbc288e9f4923f40fd23ca78a6acdc7fdf6c ] RT keeps track of the utilization on a per-rq basis with the structure avg_rt. This utilization is updated during task_tick_rt(), put_prev_task_rt() and set_next_task_rt(). However, when the current running task changes its policy, set_next_task_rt() which would usually take care of updating the utilization when the rq starts running RT tasks, will not see a such change, leaving the avg_rt structure outdated. When that very same task will be dequeued later, put_prev_task_rt() will then update the utilization, based on a wrong last_update_time, leading to a huge spike in the RT utilization signal. The signal would eventually recover from this issue after few ms. Even if no RT tasks are run, avg_rt is also updated in __update_blocked_others(). But as the CPU capacity depends partly on the avg_rt, this issue has nonetheless a significant impact on the scheduler. Fix this issue by ensuring a load update when a running task changes its policy to RT. Fixes: 371bf427 ("sched/rt: Add rt_rq utilization tracking") Signed-off-by: Vincent Donnefort Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Link: https://lore.kernel.org/r/1624271872-211872-2-git-send-email-vincent.donnefort@arm.com Signed-off-by: Sasha Levin --- kernel/sched/rt.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 8f720b71d13d..e617287052d5 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2331,13 +2331,20 @@ void __init init_sched_rt_class(void) static void switched_to_rt(struct rq *rq, struct task_struct *p) { /* - * If we are already running, then there's nothing - * that needs to be done. But if we are not running - * we may need to preempt the current running task. - * If that current running task is also an RT task + * If we are running, update the avg_rt tracking, as the running time + * will now on be accounted into the latter. + */ + if (task_current(rq, p)) { + update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0); + return; + } + + /* + * If we are not running we may need to preempt the current + * running task. If that current running task is also an RT task * then see if we can move to another run queue. */ - if (task_on_rq_queued(p) && rq->curr != p) { + if (task_on_rq_queued(p)) { #ifdef CONFIG_SMP if (p->nr_cpus_allowed > 1 && rq->rt.overloaded) rt_queue_push_tasks(rq);