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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 412BDECDFB3 for ; Sun, 15 Jul 2018 23:34:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2EDD20840 for ; Sun, 15 Jul 2018 23:34:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F2EDD20840 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.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 S1728343AbeGOX7H (ORCPT ); Sun, 15 Jul 2018 19:59:07 -0400 Received: from terminus.zytor.com ([198.137.202.136]:54559 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727007AbeGOX7G (ORCPT ); Sun, 15 Jul 2018 19:59:06 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id w6FNYAeb922192 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sun, 15 Jul 2018 16:34:10 -0700 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id w6FNYAum922189; Sun, 15 Jul 2018 16:34:10 -0700 Date: Sun, 15 Jul 2018 16:34:10 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Peter Zijlstra Message-ID: Cc: hpa@zytor.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, viresh.kumar@linaro.org Reply-To: mingo@kernel.org, torvalds@linux-foundation.org, peterz@infradead.org, hpa@zytor.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, viresh.kumar@linaro.org, vincent.guittot@linaro.org In-Reply-To: <20180705123617.GM2458@hirez.programming.kicks-ass.net> References: <20180705123617.GM2458@hirez.programming.kicks-ass.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/cpufreq: Clarify sugov_get_util() Git-Commit-ID: 45f5519ec55e75af3565dd737586d3b041834f71 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 45f5519ec55e75af3565dd737586d3b041834f71 Gitweb: https://git.kernel.org/tip/45f5519ec55e75af3565dd737586d3b041834f71 Author: Peter Zijlstra AuthorDate: Thu, 5 Jul 2018 14:36:17 +0200 Committer: Ingo Molnar CommitDate: Mon, 16 Jul 2018 00:16:29 +0200 sched/cpufreq: Clarify sugov_get_util() Add a few comments to (hopefully) clarifying some of the magic in sugov_get_util(). Signed-off-by: Peter Zijlstra (Intel) Acked-by: Viresh Kumar Cc: Linus Torvalds Cc: Morten.Rasmussen@arm.com Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Vincent Guittot Cc: claudio@evidence.eu.com Cc: daniel.lezcano@linaro.org Cc: dietmar.eggemann@arm.com Cc: joel@joelfernandes.org Cc: juri.lelli@redhat.com Cc: luca.abeni@santannapisa.it Cc: patrick.bellasi@arm.com Cc: quentin.perret@arm.com Cc: rjw@rjwysocki.net Cc: valentin.schneider@arm.com Link: http://lkml.kernel.org/r/20180705123617.GM2458@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/sched/cpufreq_schedutil.c | 75 +++++++++++++++++++++++++++++----------- 1 file changed, 54 insertions(+), 21 deletions(-) diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index c9622b3f183d..97dcd4472a0e 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -177,6 +177,26 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, return cpufreq_driver_resolve_freq(policy, freq); } +/* + * This function computes an effective utilization for the given CPU, to be + * used for frequency selection given the linear relation: f = u * f_max. + * + * The scheduler tracks the following metrics: + * + * cpu_util_{cfs,rt,dl,irq}() + * cpu_bw_dl() + * + * Where the cfs,rt and dl util numbers are tracked with the same metric and + * synchronized windows and are thus directly comparable. + * + * The cfs,rt,dl utilization are the running times measured with rq->clock_task + * which excludes things like IRQ and steal-time. These latter are then accrued + * in the irq utilization. + * + * The DL bandwidth number otoh is not a measured metric but a value computed + * based on the task model parameters and gives the minimal utilization + * required to meet deadlines. + */ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu) { struct rq *rq = cpu_rq(sg_cpu->cpu); @@ -188,47 +208,60 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu) if (rt_rq_is_runnable(&rq->rt)) return max; + /* + * Early check to see if IRQ/steal time saturates the CPU, can be + * because of inaccuracies in how we track these -- see + * update_irq_load_avg(). + */ irq = cpu_util_irq(rq); - if (unlikely(irq >= max)) return max; - /* Sum rq utilization */ + /* + * Because the time spend on RT/DL tasks is visible as 'lost' time to + * CFS tasks and we use the same metric to track the effective + * utilization (PELT windows are synchronized) we can directly add them + * to obtain the CPU's actual utilization. + */ util = cpu_util_cfs(rq); util += cpu_util_rt(rq); /* - * Interrupt time is not seen by RQS utilization so we can compare - * them with the CPU capacity + * We do not make cpu_util_dl() a permanent part of this sum because we + * want to use cpu_bw_dl() later on, but we need to check if the + * CFS+RT+DL sum is saturated (ie. no idle time) such that we select + * f_max when there is no idle time. + * + * NOTE: numerical errors or stop class might cause us to not quite hit + * saturation when we should -- something for later. */ if ((util + cpu_util_dl(rq)) >= max) return max; /* - * As there is still idle time on the CPU, we need to compute the - * utilization level of the CPU. + * There is still idle time; further improve the number by using the + * irq metric. Because IRQ/steal time is hidden from the task clock we + * need to scale the task numbers: * + * 1 - irq + * U' = irq + ------- * U + * max + */ + util *= (max - irq); + util /= max; + util += irq; + + /* * Bandwidth required by DEADLINE must always be granted while, for * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism * to gracefully reduce the frequency when no tasks show up for longer * periods of time. * - * Ideally we would like to set util_dl as min/guaranteed freq and - * util_cfs + util_dl as requested freq. However, cpufreq is not yet - * ready for such an interface. So, we only do the latter for now. + * Ideally we would like to set bw_dl as min/guaranteed freq and util + + * bw_dl as requested freq. However, cpufreq is not yet ready for such + * an interface. So, we only do the latter for now. */ - - /* Weight RQS utilization to normal context window */ - util *= (max - irq); - util /= max; - - /* Add interrupt utilization */ - util += irq; - - /* Add DL bandwidth requirement */ - util += sg_cpu->bw_dl; - - return min(max, util); + return min(max, util + sg_cpu->bw_dl); } /**