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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 2126BC43603 for ; Fri, 13 Dec 2019 09:57:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F3F6024658 for ; Fri, 13 Dec 2019 09:57:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726595AbfLMJ51 (ORCPT ); Fri, 13 Dec 2019 04:57:27 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:46132 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725747AbfLMJ50 (ORCPT ); Fri, 13 Dec 2019 04:57:26 -0500 Received: from DGGEMS403-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id ED9E138D1922D1532078; Fri, 13 Dec 2019 17:57:23 +0800 (CST) Received: from [127.0.0.1] (10.133.217.236) by DGGEMS403-HUB.china.huawei.com (10.3.19.203) with Microsoft SMTP Server id 14.3.439.0; Fri, 13 Dec 2019 17:57:17 +0800 Subject: Re: [PATCH] sched/fair: Optimize select_idle_cpu To: Peter Zijlstra CC: , , , , , , , , , "chengjian (D)" References: <20191212144102.181510-1-cj.chengjian@huawei.com> <20191212152406.GB2827@hirez.programming.kicks-ass.net> From: "chengjian (D)" Message-ID: Date: Fri, 13 Dec 2019 17:57:15 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20191212152406.GB2827@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.133.217.236] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/12/12 23:24, Peter Zijlstra wrote: > On Thu, Dec 12, 2019 at 10:41:02PM +0800, Cheng Jian wrote: > >> Fixes: 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > The 'funny' thing is that select_idle_core() actually does the right > thing. > > Copying that should work: > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e97a01..416d574dcebf 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5828,6 +5837,7 @@ static inline int select_idle_smt(struct task_struct *p, int target) > */ > static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target) > { > + struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask); > struct sched_domain *this_sd; > u64 avg_cost, avg_idle; > u64 time, cost; > @@ -5859,11 +5869,11 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t > > time = cpu_clock(this); > > - for_each_cpu_wrap(cpu, sched_domain_span(sd), target) { > + cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); > + > + for_each_cpu_wrap(cpu, cpus, target) { > if (!--nr) > return si_cpu; > - if (!cpumask_test_cpu(cpu, p->cpus_ptr)) > - continue; > if (available_idle_cpu(cpu)) > break; > if (si_cpu == -1 && sched_idle_cpu(cpu)) > > . in select_idle_smt() /*  * Scan the local SMT mask for idle CPUs.  */ static int select_idle_smt(struct task_struct *p, int target) {     int cpu, si_cpu = -1;     if (!static_branch_likely(&sched_smt_present))         return -1;     for_each_cpu(cpu, cpu_smt_mask(target)) {         if (!cpumask_test_cpu(cpu, p->cpus_ptr))             continue;         if (available_idle_cpu(cpu))             return cpu;         if (si_cpu == -1 && sched_idle_cpu(cpu))             si_cpu = cpu;     }     return si_cpu; } Why don't we do the same thing in this function, although cpu_smt_present () often has few CPUs. it is better to determine the 'p->cpus_ptr' first.