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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 EC83AC43603 for ; Fri, 13 Dec 2019 08:37:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C07192465E for ; Fri, 13 Dec 2019 08:37:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="VH7XmMTY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726592AbfLMIhl (ORCPT ); Fri, 13 Dec 2019 03:37:41 -0500 Received: from mail-lf1-f66.google.com ([209.85.167.66]:35794 "EHLO mail-lf1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725818AbfLMIhl (ORCPT ); Fri, 13 Dec 2019 03:37:41 -0500 Received: by mail-lf1-f66.google.com with SMTP id 15so1350843lfr.2 for ; Fri, 13 Dec 2019 00:37:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=IViYxUVtxhmy+DhoYbq41mJ5frzvzah03nv9ueXSwIM=; b=VH7XmMTYa7gkUtI0dk0K3xQG+rHb2TE89MdDnwaMmu/omPIeRmBQT7R00hlMq46Vop n/L7FWABeXBTjQHxUhlvc3iobGa8yZ3q34qp+H9FTf8HLq36L37n4C/BjbMXVEQsKxcH qq8KUavWNUAneUOUX31KLR0ZjLlgFCKGPMRPHnhWbqNaY9cXTQjAYj50EF5ZRpZbmPpK /4X2wO+R+/qBv5J0kAXLzlCOg5Afx6y6VmzNEIzBMLDGTFYbbrTZDcuFFACi/1dq7HE1 Vevyj4b4HzDEbN8cwGI2xILgLmVjGeKKFYPrA3BMNWgR08JCBFHnwcyUDYFATs1rjXn2 yL7A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=IViYxUVtxhmy+DhoYbq41mJ5frzvzah03nv9ueXSwIM=; b=Pl2rlXGx1R4FRvyMOPZgty6xQNtVwT1Pw8FnaBuoWpCkzxMaKCffm236ejGxGtahY9 OTCqc/u0NTsM5+zv+0lYI1cMe/LjGICiNaC54UmyxNHST6XzcZdT69TjjYqfj41LLsfJ I0RHW2yp0JYibaQr4XQxO5e2sNcvkSmxZMq/N2PS71pJ+HZIGO8i/93xwKe+tl1jkcvB +49DzwMGYC4yrxBiQeJ6pm+rH3p2FNkcXST7KmzQVp2dVzIhVLYSGMFo3TaEHbj5Cye+ WvZuuwK/tWugrhduHvU4FoYuSjSFzb0poohYWVj4RyjE+dR8B2ede29spco14ps4Qz+g tbqA== X-Gm-Message-State: APjAAAUK0AMD0sLQZtBE0pF3gcq+DYAYLDZiJdCf98Wwo5pj+ESiqzTj 6jSMtCShHLDHWNMTYCzq+BhCc8D7i4l4VZ7HXY4GOw== X-Google-Smtp-Source: APXvYqz6KzhzKX65oJt06EFCN7iEWegIfKRRv5k7uFFbbaYlDeM5+NLKuOtf+MEbqH6/PWvxcsi1B/JW7yfDPu2sQEk= X-Received: by 2002:ac2:43a7:: with SMTP id t7mr7603624lfl.125.1576226259104; Fri, 13 Dec 2019 00:37:39 -0800 (PST) MIME-Version: 1.0 References: <20191213024530.28052-1-cj.chengjian@huawei.com> In-Reply-To: <20191213024530.28052-1-cj.chengjian@huawei.com> From: Vincent Guittot Date: Fri, 13 Dec 2019 09:37:27 +0100 Message-ID: Subject: Re: [PATCH v2] sched/fair: Optimize select_idle_cpu To: Cheng Jian Cc: Ingo Molnar , Peter Zijlstra , linux-kernel , chenwandun@huawei.com, Xie XiuQi , liwei391@huawei.com, huawei.libin@huawei.com, bobo.shaobowang@huawei.com, Juri Lelli Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 13 Dec 2019 at 03:48, 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: Vincent Guittot > --- > 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)) > -- > 2.20.1 >