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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 D7FB5C2BA83 for ; Fri, 14 Feb 2020 16:40:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B7A702187F for ; Fri, 14 Feb 2020 16:40:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390609AbgBNQkI (ORCPT ); Fri, 14 Feb 2020 11:40:08 -0500 Received: from foss.arm.com ([217.140.110.172]:39292 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405845AbgBNQkD (ORCPT ); Fri, 14 Feb 2020 11:40:03 -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 9A8C1113E; Fri, 14 Feb 2020 08:40:02 -0800 (PST) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 30CC23F6CF; Fri, 14 Feb 2020 08:40:01 -0800 (PST) From: Qais Yousef To: Ingo Molnar , Peter Zijlstra , Steven Rostedt , Pavan Kondeti , Dietmar Eggemann Cc: Juri Lelli , Vincent Guittot , Ben Segall , Mel Gorman , linux-kernel@vger.kernel.org, Qais Yousef Subject: [PATCH 3/3] sched/rt: fix pushing unfit tasks to a better CPU Date: Fri, 14 Feb 2020 16:39:49 +0000 Message-Id: <20200214163949.27850-4-qais.yousef@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200214163949.27850-1-qais.yousef@arm.com> References: <20200214163949.27850-1-qais.yousef@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If a task was running on unfit CPU we could ignore migrating if the priority level of the new fitting CPU is the *same* as the unfit one. Add an extra check to select_task_rq_rt() to allow the push in case: * old_cpu.highest_priority == new_cpu.highest_priority * task_fits(p, new_cpu) Signed-off-by: Qais Yousef --- I was seeing some delays in migrating a task to a big CPU sometimes although it was free, and I think this fixes it. TBH, I fail to see how the check of p->prio < cpu_rq(target)->rt.highest_prio.curr is necessary as find_lowest_rq() surely implies the above condition by definition? Unless we're fighting a race condition here where the rt_rq priority has changed between the time we selected the lowest_rq and taking the decision to migrate, then this makes sense. kernel/sched/rt.c | 34 +++++++++++++++++++++++++--------- 1 file changed, 25 insertions(+), 9 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 0c8bac134d3a..5ea235f2cfe8 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1430,7 +1430,7 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) { struct task_struct *curr; struct rq *rq; - bool test; + bool test, fit; /* For anything but wake ups, just return the task_cpu */ if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK) @@ -1471,16 +1471,32 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) unlikely(rt_task(curr)) && (curr->nr_cpus_allowed < 2 || curr->prio <= p->prio); - if (test || !rt_task_fits_capacity(p, cpu)) { + fit = rt_task_fits_capacity(p, cpu); + + if (test || !fit) { int target = find_lowest_rq(p); - /* - * Don't bother moving it if the destination CPU is - * not running a lower priority task. - */ - if (target != -1 && - p->prio < cpu_rq(target)->rt.highest_prio.curr) - cpu = target; + if (target != -1) { + /* + * Don't bother moving it if the destination CPU is + * not running a lower priority task. + */ + if (p->prio < cpu_rq(target)->rt.highest_prio.curr) { + + cpu = target; + + } else if (p->prio == cpu_rq(target)->rt.highest_prio.curr) { + + /* + * If the priority is the same and the new CPU + * is a better fit, then move, otherwise don't + * bother here either. + */ + fit = rt_task_fits_capacity(p, target); + if (fit) + cpu = target; + } + } } rcu_read_unlock(); -- 2.17.1