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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 93884C2BB55 for ; Thu, 16 Apr 2020 17:23:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7974221924 for ; Thu, 16 Apr 2020 17:23:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390197AbgDPRXj (ORCPT ); Thu, 16 Apr 2020 13:23:39 -0400 Received: from foss.arm.com ([217.140.110.172]:38442 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388338AbgDPRXg (ORCPT ); Thu, 16 Apr 2020 13:23:36 -0400 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 1E25830E; Thu, 16 Apr 2020 10:23:36 -0700 (PDT) Received: from [192.168.1.19] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 616E03F73D; Thu, 16 Apr 2020 10:23:33 -0700 (PDT) Subject: Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice To: Joel Fernandes , Qais Yousef Cc: Peter Zijlstra , Patrick Bellasi , Subhra Mazumdar , linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de, steven.sistare@oracle.com, dhaval.giani@oracle.com, daniel.lezcano@linaro.org, vincent.guittot@linaro.org, viresh.kumar@linaro.org, tim.c.chen@linux.intel.com, mgorman@techsingularity.net, parth@linux.ibm.com References: <20190830174944.21741-1-subhra.mazumdar@oracle.com> <20190830174944.21741-2-subhra.mazumdar@oracle.com> <20190905083127.GA2332@hirez.programming.kicks-ass.net> <87r24v2i14.fsf@arm.com> <20190905104616.GD2332@hirez.programming.kicks-ass.net> <20190905111346.2w6kuqrdvaqvgilu@e107158-lin.cambridge.arm.com> <20190905113002.GK2349@hirez.programming.kicks-ass.net> <20190905114725.ehi5ea6qg3rychlz@e107158-lin.cambridge.arm.com> <20200416000235.GA211099@google.com> From: Dietmar Eggemann Message-ID: <730928f8-b48b-ea3a-149a-18932eb18c90@arm.com> Date: Thu, 16 Apr 2020 19:23:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200416000235.GA211099@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Joel, On 16.04.20 02:02, Joel Fernandes wrote: > On Thu, Sep 05, 2019 at 12:47:26PM +0100, Qais Yousef wrote: >> On 09/05/19 13:30, Peter Zijlstra wrote: >>> On Thu, Sep 05, 2019 at 12:13:47PM +0100, Qais Yousef wrote: >>>> On 09/05/19 12:46, Peter Zijlstra wrote: >>> >>>>> This is important because we want to be able to bias towards less >>>>> importance to (tail) latency as well as more importantance to (tail) >>>>> latency. >>>>> >>>>> Specifically, Oracle wants to sacrifice (some) latency for throughput. >>>>> Facebook OTOH seems to want to sacrifice (some) throughput for latency. >>>> >>>> Another use case I'm considering is using latency-nice to prefer an idle CPU if >>>> latency-nice is set otherwise go for the most energy efficient CPU. >>>> >>>> Ie: sacrifice (some) energy for latency. >>>> >>>> The way I see interpreting latency-nice here as a binary switch. But >>>> maybe we can use the range to select what (some) energy to sacrifice >>>> mean here. Hmmm. >>> >>> It cannot be binary, per definition is must be ternary, that is, <0, ==0 >>> and >0 (or middle value if you're of that persuasion). >> >> I meant I want to use it as a binary. >> >>> >>> In your case, I'm thinking you mean >0, we want to lower the latency. >> >> Yes. As long as there's an easy way to say: does this task care about latency >> or not I'm good. > > Qais, Peter, all, > > For ChromeOS (my team), we are planning to use the upstream uclamp mechanism > instead of the out-of-tree schedtune mechanism to provide EAS with the > latency-sensitivity (binary/ternary) hint. ChromeOS is thankfully quite a bit > upstream focussed :) > > However, uclamp is missing an attribute to provide this biasing to EAS as we > know. > > What was the consensus on adding a per-task attribute to uclamp for providing > this? Happy to collaborate on this front. We're planning to have a session about this topic (latency-nice attribute per task group) during the virtual Pisa OSPM summit retis.sssup.it/ospm-summit in May this year. There are two presentations/discussions planned: "Introducing Latency Nice for Scheduler Hints and Optimizing Scheduler Task Wakeup" and "The latency nice use case for Energy-Aware-Scheduling (EAS) in Android Common Kernel (ACK)" We'll probably merge those two into one presentation/discussion. So far we have Parth's per-task implementation https://lore.kernel.org/lkml/20200228090755.22829-1-parth@linux.ibm.com What's missing is the per-taskgroup implementation, at least from the standpoint of ACK. The (mainline) EAS use-case for latency nice is already in ACK (android-5.4): https://android.googlesource.com/kernel/common/+/760b82c9b88d2c8125abfc5f732cc3cd460b2a54