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, URIBL_BLOCKED,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 7D803C34991 for ; Fri, 13 Dec 2019 20:36:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE131246A2 for ; Fri, 13 Dec 2019 20:36:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726863AbfLMLsX (ORCPT ); Fri, 13 Dec 2019 06:48:23 -0500 Received: from foss.arm.com ([217.140.110.172]:56292 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725980AbfLMLsW (ORCPT ); Fri, 13 Dec 2019 06:48:22 -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 5ED401045; Fri, 13 Dec 2019 03:48:22 -0800 (PST) Received: from [10.1.194.37] (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0AD1B3F718; Fri, 13 Dec 2019 03:48:20 -0800 (PST) Subject: Re: [PATCH v2] sched/fair: Optimize select_idle_cpu To: Cheng Jian , mingo@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org Cc: chenwandun@huawei.com, xiexiuqi@huawei.com, liwei391@huawei.com, huawei.libin@huawei.com, bobo.shaobowang@huawei.com, juri.lelli@redhat.com, vincent.guittot@linaro.org References: <20191213024530.28052-1-cj.chengjian@huawei.com> From: Valentin Schneider Message-ID: Date: Fri, 13 Dec 2019 11:48:20 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191213024530.28052-1-cj.chengjian@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/12/2019 02:45, Cheng Jian wrote: > select_idle_cpu() will scan the LLC domain for idle CPUs, > it's always expensive. so the next commit : > > 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > > introduces a way to limit how many CPUs we scan. > > But it consume some CPUs out of 'nr' that are not allowed > for the task and thus waste our attempts. The function > always return nr_cpumask_bits, and we can't find a CPU > which our task is allowed to run. > > Cpumask may be too big, similar to select_idle_core(), use > per_cpu_ptr 'select_idle_mask' to prevent stack overflow. > > Fixes: 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > Signed-off-by: Cheng Jian Reviewed-by: Valentin Schneider > --- > kernel/sched/fair.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e97a01..d48244388ce9 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5828,6 +5828,7 @@ 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 +5860,11 @@ 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)) >