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 0E750C433F5 for ; Thu, 30 Aug 2018 09:57:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AB2392073D for ; Thu, 30 Aug 2018 09:57:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB2392073D 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 S1728245AbeH3N7O (ORCPT ); Thu, 30 Aug 2018 09:59:14 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:38686 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728082AbeH3N7O (ORCPT ); Thu, 30 Aug 2018 09:59:14 -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 25A797A9; Thu, 30 Aug 2018 02:57:54 -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 30BE93F721; Thu, 30 Aug 2018 02:57:50 -0700 (PDT) Date: Thu, 30 Aug 2018 10:57:45 +0100 From: Quentin Perret To: Patrick Bellasi Cc: peterz@infradead.org, 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, 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 07/14] sched/topology: Introduce sched_energy_present static key Message-ID: <20180830095723.4qqbpft7gpbtgkhd@queper01-lin> References: <20180820094420.26590-1-quentin.perret@arm.com> <20180820094420.26590-8-quentin.perret@arm.com> <20180829165058.GR2960@e110439-lin> <20180829172004.afbe2oukprvptqs2@queper01-lin> <20180830092329.GS2960@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180830092329.GS2960@e110439-lin> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Patrick, On Thursday 30 Aug 2018 at 10:23:29 (+0100), Patrick Bellasi wrote: > Yes, dunno if it's just me but perhaps a bit of rephrasing could help. Ok, so what about something a little bit more explicit like: /* * The complexity of the Energy Model is defined as: * * C = nr_pd * (nr_cpus + nr_cs) * * with parameters defined as: * - nr_pd: the number of performance domains * - nr_cpus: the number of CPUs * - nr_cs: the sum of the number of capacity states of all performance * domains (for example, on a system with 2 performance domains, * with 10 capacity states each, nr_cs = 2 * 10 = 20). * * It is generally not a good idea to use such a model in the wake-up path on * very complex platforms because of the associated scheduling overheads. The * arbitrary constraint below prevents that. It makes EAS usable up to 16 CPUs * with per-CPU DVFS and less than 8 capacity states each, for example. */ > Alternatively, why not having this comment and check after patches > 11 and 12 ? Oh, you don't like it here ? What's wrong with it :-) ? > Right... I was totally confused by the idea that we don't > run EAS if we just have 1 CPU per PD... my bad! > > Although on those systems, since we don't have idle costs, should not > be a spreading strategy always the best from an energy efficiency > standpoint ? Even with per-CPU DVFS, if you have big and little CPUs it matters _where_ you execute a task, and you'll still need an Energy Model to make good decisions in a generic way. But yes, there is definitely some room for improvement for those platforms. That's something we could improve later on top of this series I suppose. Thanks for looking at the patches ! Quentin