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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 5B48AC43142 for ; Thu, 2 Aug 2018 16:21:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1D1322152E for ; Thu, 2 Aug 2018 16:21:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1D1322152E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729982AbeHBSNb (ORCPT ); Thu, 2 Aug 2018 14:13:31 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:60310 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726221AbeHBSNb (ORCPT ); Thu, 2 Aug 2018 14:13:31 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 086DE80D; Thu, 2 Aug 2018 09:21:40 -0700 (PDT) Received: from queper01-lin (queper01-lin.emea.arm.com [10.4.13.27]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 12FF83F5D0; Thu, 2 Aug 2018 09:21:35 -0700 (PDT) Date: Thu, 2 Aug 2018 17:21:34 +0100 From: Quentin Perret To: Peter Zijlstra Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, gregkh@linuxfoundation.org, mingo@redhat.com, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, patrick.bellasi@arm.com, valentin.schneider@arm.com, vincent.guittot@linaro.org, thara.gopinath@linaro.org, viresh.kumar@linaro.org, tkjos@google.com, joel@joelfernandes.org, smuckle@google.com, adharmap@quicinc.com, skannan@quicinc.com, pkondeti@codeaurora.org, juri.lelli@redhat.com, edubezval@gmail.com, srinivas.pandruvada@linux.intel.com, currojerez@riseup.net, javi.merino@kernel.org Subject: Re: [PATCH v5 12/14] sched/fair: Select an energy-efficient CPU on task wake-up Message-ID: <20180802162132.7ur5poka5m7r2io2@queper01-lin> References: <20180724122521.22109-1-quentin.perret@arm.com> <20180724122521.22109-13-quentin.perret@arm.com> <20180802135426.GX2476@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180802135426.GX2476@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 02 Aug 2018 at 15:54:26 (+0200), Peter Zijlstra wrote: > On Tue, Jul 24, 2018 at 01:25:19PM +0100, Quentin Perret wrote: > > @@ -6385,18 +6492,26 @@ static int > > select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags) > > { > > struct sched_domain *tmp, *sd = NULL; > > + struct freq_domain *fd; > > int cpu = smp_processor_id(); > > int new_cpu = prev_cpu; > > - int want_affine = 0; > > + int want_affine = 0, want_energy = 0; > > int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING); > > > > + rcu_read_lock(); > > if (sd_flag & SD_BALANCE_WAKE) { > > record_wakee(p); > > - want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) > > - && cpumask_test_cpu(cpu, &p->cpus_allowed); > > + fd = rd_freq_domain(cpu_rq(cpu)->rd); > > + want_energy = fd && !READ_ONCE(cpu_rq(cpu)->rd->overutilized); > > + want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) && > > + cpumask_test_cpu(cpu, &p->cpus_allowed); > > + } > > + > > + if (want_energy) { > > + new_cpu = find_energy_efficient_cpu(p, prev_cpu, fd); > > + goto unlock; > > } > > > > And I suppose you rely on the compiler to optimize that for the static > key inside rd_freq_domain()... Does it do a good job of that? I does for sure when CONFIG_ENERGY_MODEL=n since rd_freq_domain() is stubbed to false, but that's an easy one ;-) > > That is, would not something like: > > > rcu_read_lock(); > if (sd_flag & SD_BALANCE_WAKE) { > record_wakee(p); > > if (static_branch_unlikely(&sched_energy_present)) { > struct root_domain *rd = cpu_rq(cpu)->rd; > struct freq_domain *fd = rd_freq_domain(rd); > > if (fd && !READ_ONCE(rd->overutilized)) { > new_cpu = find_energy_efficient_cpu(p, prev_cpu, fd); > goto unlock; > } > } > > /* ... */ > } > > > Be far more clear ? It is clearer. Having the static key check in rd_freq_domain() makes the change to find_busiest_group() smaller, but I can totally change it with something like the above. I'll do that in v6. Thanks, Quentin