From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752128AbeEQTK1 (ORCPT ); Thu, 17 May 2018 15:10:27 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:58150 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751530AbeEQTKZ (ORCPT ); Thu, 17 May 2018 15:10:25 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 0FFCC601D7 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=skannan@codeaurora.org Message-ID: <5AFDD39E.6040203@codeaurora.org> Date: Thu, 17 May 2018 12:10:22 -0700 From: Saravana Kannan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Joel Fernandes CC: Quentin Perret , Dietmar Eggemann , Viresh Kumar , linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , linux-pm@vger.kernel.org, Pavan Kondeti , "Rafael J . Wysocki" , Juri Lelli , Joel Fernandes , Patrick Bellasi Subject: Re: [PATCH] Revert "cpufreq: schedutil: Don't restrict kthread to related_cpus unnecessarily" References: <20180508073340.13114-1-dietmar.eggemann@arm.com> <20180508082242.bre6sjfvefhz6xc3@vireshk-i7> <8cf21b1a-ca6e-fed7-43c5-94c66ff5986b@arm.com> <20180508094237.GA3752@e108498-lin.cambridge.arm.com> <20180513051933.GA64158@joelaf.mtv.corp.google.com> In-Reply-To: <20180513051933.GA64158@joelaf.mtv.corp.google.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/12/2018 10:19 PM, Joel Fernandes wrote: > On Tue, May 08, 2018 at 10:42:37AM +0100, Quentin Perret wrote: >> On Tuesday 08 May 2018 at 11:09:57 (+0200), Dietmar Eggemann wrote: >>> On 05/08/2018 10:22 AM, Viresh Kumar wrote: >>>> On 08-05-18, 08:33, Dietmar Eggemann wrote: >>>>> This reverts commit e2cabe48c20efb174ce0c01190f8b9c5f3ea1d13. >>>>> >>>>> Lifting the restriction that the sugov kthread is bound to the >>>>> policy->related_cpus for a system with a slow switching cpufreq driver, >>>>> which is able to perform DVFS from any cpu (e.g. cpufreq-dt), is not >>>>> only not beneficial it also harms Enery-Aware Scheduling (EAS) on >>>>> systems with asymmetric cpu capacities (e.g. Arm big.LITTLE). >>>>> >>>>> The sugov kthread which does the update for the little cpus could >>>>> potentially run on a big cpu. It could prevent that the big cluster goes >>>>> into deeper idle states although all the tasks are running on the little >>>>> cluster. >>>> >>>> I think the original patch did the right thing, but that doesn't suit >>>> everybody as you explained. >>>> >>>> I wouldn't really revert the patch but fix my platform's cpufreq >>>> driver to set dvfs_possible_from_any_cpu = false, so that other >>>> platforms can still benefit from the original commit. >>> >>> This would make sure that the kthreads are bound to the correct set of cpus >>> for platforms with those cpufreq drivers (cpufreq-dt (h960), scmi-cpufreq, >>> scpi-cpufreq) but it will also change the logic (e.g. >>> sugov_should_update_freq() -> cpufreq_can_do_remote_dvfs()). >>> >>> I'm still struggling to understand when a driver/platform should set >>> dvfs_possible_from_any_cpu to true and what the actual benefit would be. >> >> I assume it might be beneficial to have the kthread moving around freely >> in some cases, but since it is a SCHED_DEADLINE task now it can't really >> migrate anywhere anyway. So I'm not sure either if this commits still makes >> sense now. Or is there another use case for this ? > > The usecase I guess is, as Dietmar was saying, that it makes sense for > kthread to update its own cluster and not disturb other clusters or random > CPUs. I agree with this point. I agree with Viresh. Also, why exactly did we make it deadline instead of RT? Was RT not getting scheduled quick enough? Is it because Android creates a lot of RT threads? -Saravana -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project