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=-15.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 809B5C433DB for ; Thu, 25 Feb 2021 11:46:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 36E5A64F13 for ; Thu, 25 Feb 2021 11:46:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234308AbhBYLqT (ORCPT ); Thu, 25 Feb 2021 06:46:19 -0500 Received: from foss.arm.com ([217.140.110.172]:55586 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229561AbhBYLqQ (ORCPT ); Thu, 25 Feb 2021 06:46:16 -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 BAF5AD6E; Thu, 25 Feb 2021 03:45:30 -0800 (PST) Received: from [192.168.1.15] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3EA653F73D; Thu, 25 Feb 2021 03:45:29 -0800 (PST) Subject: Re: [PATCH v2 1/2] sched/fair: Fix task utilization accountability in compute_energy() To: vincent.donnefort@arm.com, peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, qperret@google.com, patrick.bellasi@matbug.net, valentin.schneider@arm.com References: <20210225083612.1113823-1-vincent.donnefort@arm.com> <20210225083612.1113823-2-vincent.donnefort@arm.com> From: Dietmar Eggemann Message-ID: Date: Thu, 25 Feb 2021 12:45:06 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210225083612.1113823-2-vincent.donnefort@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/02/2021 09:36, vincent.donnefort@arm.com wrote: > From: Vincent Donnefort [...] > cpu_util_next() estimates the CPU utilization that would happen if the > task was placed on dst_cpu as follows: > > max(cpu_util + task_util, cpu_util_est + _task_util_est) > > The task contribution to the energy delta can then be either: > > (1) _task_util_est, on a mostly idle CPU, where cpu_util is close to 0 > and _task_util_est > cpu_util. > (2) task_util, on a mostly busy CPU, where cpu_util > _task_util_est. > > (cpu_util_est doesn't appear here. It is 0 when a CPU is idle and > otherwise must be small enough so that feec() takes the CPU as a > potential target for the task placement) I still don't quite get the reasoning for (2) why task_util is used as task contribution. So we use 'cpu_util + task_util' instead of 'cpu_util_est + _task_util_est' in (2). I.e. since _task_util_est is always >= task_util during wakeup, cpu_util must be > cpu_util_est (by more than _task_util_est - task_util). I can see it for a CPU whose cpu_util has a fair amount of contributions from blocked tasks which cpu_util_est wouldn't have. [...] > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 7043bb0f2621..146ac9fec4b6 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6573,8 +6573,24 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd) > * its pd list and will not be accounted by compute_energy(). > */ > for_each_cpu_and(cpu, pd_mask, cpu_online_mask) { > - unsigned long cpu_util, util_cfs = cpu_util_next(cpu, p, dst_cpu); > - struct task_struct *tsk = cpu == dst_cpu ? p : NULL; > + unsigned long util_freq = cpu_util_next(cpu, p, dst_cpu); > + unsigned long cpu_util, util_running = util_freq; > + struct task_struct *tsk = NULL; > + > + /* > + * When @p is placed on @cpu: > + * > + * util_running = max(cpu_util, cpu_util_est) + > + * max(task_util, _task_util_est) > + * > + * while cpu_util_next is: max(cpu_util + task_util, > + * cpu_util_est + _task_util_est) > + */ Nit pick: s/on @cpu/on @dst_cpu ? s/while cpu_util_next is/while cpu_util_next(cpu, p, cpu) would be If dst_cpu != cpu (including dst_cpu == -1) task_util and _task_util_est are not added to util resp. util_est. Not sure if this is clear from the source code here? [...] Reviewed-by: Dietmar Eggemann