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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_SANE_1 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 D417FC433E0 for ; Tue, 16 Jun 2020 06:09:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 91C422082F for ; Tue, 16 Jun 2020 06:09:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726972AbgFPGJp (ORCPT ); Tue, 16 Jun 2020 02:09:45 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:56204 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725775AbgFPGJo (ORCPT ); Tue, 16 Jun 2020 02:09:44 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=rocking@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0U.l9R21_1592287779; Received: from IT-C02ZG85SLVDL.local(mailfrom:rocking@linux.alibaba.com fp:SMTPD_---0U.l9R21_1592287779) by smtp.aliyun-inc.com(127.0.0.1); Tue, 16 Jun 2020 14:09:40 +0800 Subject: Re: [PATCH] sched/fair: Optimize dequeue_task_fair() To: Vincent Guittot Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , linux-kernel References: <6f2f195aea48bc50187dfb064aa530ba132be01b.1592230286.git.rocking@linux.alibaba.com> From: Peng Wang Message-ID: <60d6eec1-4406-655c-c329-fc1c915a7721@linux.alibaba.com> Date: Tue, 16 Jun 2020 14:09:39 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/15/20 11:09 PM, Vincent Guittot wrote: > On Mon, 15 Jun 2020 at 16:20, Peng Wang wrote: >> >> While looking at enqueue_task_fair and dequeue_task_fair, it occurred >> to me that dequeue_task_fair can also be optimized as Vincent described >> in commit 7d148be69e3a ("sched/fair: Optimize enqueue_task_fair()"). > > good point > >> >> dequeue_throttle label can ensure se not to be NULL, and se is >> always NULL when reaching root level. >> >> Signed-off-by: Peng Wang >> --- >> kernel/sched/fair.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index cbcb2f7..e6be952 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -5614,10 +5614,10 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) >> >> } >> >> -dequeue_throttle: >> - if (!se) >> - sub_nr_running(rq, 1); >> + /* At this point se is NULL and we are at root level*/ >> + sub_nr_running(rq, 1); >> >> +dequeue_throttle: >> /* balance early to pull high priority tasks */ >> if (unlikely(!was_sched_idle && sched_idle_rq(rq))) >> rq->next_balance = jiffies; > > You can move the label here because sched_idle_rq() uses > rq->nr-running and rq->cfs.idle_h_nr_running so they will not change > if we jump to the label before reaching root level Yes, then we can also skip the early balance check. > >> -- >> 2.9.5 >>