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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,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 B5A3EC433F5 for ; Tue, 4 Sep 2018 10:59:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 547EC2077C for ; Tue, 4 Sep 2018 10:59:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 547EC2077C 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 S1727406AbeIDPXz (ORCPT ); Tue, 4 Sep 2018 11:23:55 -0400 Received: from foss.arm.com ([217.140.101.70]:40686 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727024AbeIDPXz (ORCPT ); Tue, 4 Sep 2018 11:23:55 -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 1A6197A9; Tue, 4 Sep 2018 03:59:17 -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 255B33F5BC; Tue, 4 Sep 2018 03:59:13 -0700 (PDT) Date: Tue, 4 Sep 2018 11:59:08 +0100 From: Quentin Perret To: peterz@infradead.org, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Cc: 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@codeaurora.org, skannan@codeaurora.org, 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 v6 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil Message-ID: <20180904105906.t5i7twyyt2omc45b@queper01-lin> References: <20180820094420.26590-1-quentin.perret@arm.com> <20180820094420.26590-14-quentin.perret@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180820094420.26590-14-quentin.perret@arm.com> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday 20 Aug 2018 at 10:44:19 (+0100), Quentin Perret wrote: > Energy Aware Scheduling (EAS) is designed with the assumption that > frequencies of CPUs follow their utilization value. When using a CPUFreq > governor other than schedutil, the chances of this assumption being true > are small, if any. When schedutil is being used, EAS' predictions are at > least consistent with the frequency requests. Although those requests > have no guarantees to be honored by the hardware, they should at least > guide DVFS in the right direction and provide some hope in regards to the > EAS model being accurate. > > To make sure EAS is only used in a sane configuration, create a strong > dependency on schedutil being used. Since having sugov compiled-in does > not provide that guarantee, extend the existing CPUFreq policy notifier > with a new case on governor changes. That allows the scheduler to > register a callback on this notifier to rebuild the scheduling domains > when governors are changed, and enable/disable EAS accordingly. > > cc: Ingo Molnar > cc: Peter Zijlstra > Signed-off-by: Quentin Perret > > --- > This patch could probably be squashed into another one, but I kept it > separate to ease the review. Also, it's probably optional as not having > it will not 'break' things per se. > > I went for the smallest possible solution I could find, which has the > good side of being simple, but it's definitely not the only one. > > Another possibility would be to hook things in sugov_start() and > sugov_stop(), but that requires some more work. In this case, it > wouldn't be possible to just re-build the sched_domains() from there, > because when sugov_stop() is called, the 'governor' field of the policy > hasn't been updated yet, so the condition (if gov == schedutil) in > build_freq_domains() doesn't work. > > To workaround the issue we'll need to find a way to pass a cpumask to > the topology code to specifically say 'sugov has been stopped on these > CPUs'. That would mean more code to handle that, but that would also > mean we don't have to mess around with the CPUFreq notifiers ... > > Not sure what's best, so all feedback is more than welcome. Hi, Does anybody have concerns with this patch ? Is it a reasonable option to use the CPUFreq notifiers in this case ? If there is anything I can do to ease the review please let me know. Also, is there any hope that the 12 first patches could make it in 4.20 on their own ? Or is it already too late ? Thanks, Quentin