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,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 43DC4C64EBC for ; Thu, 4 Oct 2018 11:58:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F3E4621473 for ; Thu, 4 Oct 2018 11:58:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F3E4621473 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 S1727486AbeJDSvo (ORCPT ); Thu, 4 Oct 2018 14:51:44 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:35310 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727256AbeJDSvo (ORCPT ); Thu, 4 Oct 2018 14:51:44 -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 E43AE7A9; Thu, 4 Oct 2018 04:58:46 -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 C73793F5A0; Thu, 4 Oct 2018 04:58:42 -0700 (PDT) Date: Thu, 4 Oct 2018 12:58:41 +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@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 v7 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil Message-ID: <20181004115839.c5g2fsehszbvwoqq@queper01-lin> References: <20180912091309.7551-1-quentin.perret@arm.com> <20180912091309.7551-14-quentin.perret@arm.com> <20181004105023.GE19252@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181004105023.GE19252@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 04 Oct 2018 at 12:50:23 (+0200), Peter Zijlstra wrote: > On Wed, Sep 12, 2018 at 10:13:08AM +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, make CPUFreq call a scheduler function on > > on governor changes hence letting it rebuild the scheduling domains, > > check the governors of the online CPUs, and enable/disable EAS > > accordingly. > > So this patch disables EAS when we change cpufreq gov. How about we > force select schedutil and disallow changing it when EAS is enabled? > > Instead of silently disabling EAS when we frob the governor? By doing it this way I think we have a better integration with things like that exclusive cpusets. In the end, EAS is enabled in a per-root_domain basis. So, say you have two root domains, A and B. EAS is enabled on A and disabled on B (because it doesn't have SD_ASYM_CPUCAPACITY or something). Should you be forced to use sugov on the CPUs of B to run EAS on A ? If there is a cpufreq policy covering only the CPUs of B, I'd say probably no. Now I get the argument that this is happening silently as-is, so we can do better. How about we put a message in dmesg we EAS gets disabled in case of governor changes ? Also, I'm currently working on a doc patch for EAS ATM (to be posted soon), so I can (and will) make it very clear there that you _must_ use sugov to use EAS. Would that work ? Thanks, Quentin