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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 F4119C433B4 for ; Thu, 15 Apr 2021 15:17:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CBBDA6115C for ; Thu, 15 Apr 2021 15:17:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235319AbhDOPR7 (ORCPT ); Thu, 15 Apr 2021 11:17:59 -0400 Received: from foss.arm.com ([217.140.110.172]:48866 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236724AbhDOPPN (ORCPT ); Thu, 15 Apr 2021 11:15:13 -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 22208106F; Thu, 15 Apr 2021 08:14:50 -0700 (PDT) Received: from e120877-lin.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DEF823FA35; Thu, 15 Apr 2021 08:14:48 -0700 (PDT) Date: Thu, 15 Apr 2021 16:14:46 +0100 From: Vincent Donnefort To: Quentin Perret Cc: peterz@infradead.org, rjw@rjwysocki.net, viresh.kumar@linaro.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, ionela.voinescu@arm.com, lukasz.luba@arm.com, dietmar.eggemann@arm.com Subject: Re: [PATCH] PM / EM: Inefficient OPPs detection Message-ID: <20210415151446.GC391924@e120877-lin.cambridge.arm.com> References: <1617901829-381963-1-git-send-email-vincent.donnefort@arm.com> <1617901829-381963-2-git-send-email-vincent.donnefort@arm.com> <20210415143453.GB391924@e120877-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 15, 2021 at 02:59:54PM +0000, Quentin Perret wrote: > On Thursday 15 Apr 2021 at 15:34:53 (+0100), Vincent Donnefort wrote: > > On Thu, Apr 15, 2021 at 01:16:35PM +0000, Quentin Perret wrote: > > > On Thursday 08 Apr 2021 at 18:10:29 (+0100), Vincent Donnefort wrote: > > > > --- a/kernel/sched/cpufreq_schedutil.c > > > > +++ b/kernel/sched/cpufreq_schedutil.c > > > > @@ -10,6 +10,7 @@ > > > > > > > > #include "sched.h" > > > > > > > > +#include > > > > #include > > > > #include > > > > > > > > @@ -164,6 +165,9 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, > > > > > > > > freq = map_util_freq(util, freq, max); > > > > > > > > + /* Avoid inefficient performance states */ > > > > + freq = em_pd_get_efficient_freq(em_cpu_get(policy->cpu), freq); > > > > > > I remember this was discussed when Douglas sent his patches some time > > > ago, but I still find it sad we index the EM table here but still > > > re-index the cpufreq frequency table later :/ > > > > > > Yes in your case this lookup is very inexpensive, but still. EAS relies > > > on the EM's table matching cpufreq's accurately, so this second lookup > > > still feels rather unnecessary ... > > > > To get only a single lookup, we would need to bring the inefficiency knowledge > > directly to the cpufreq framework. But it has its own limitations: > > > > The cpufreq driver can have its own resolve_freq() callback, which means that > > not all the drivers would benefit from that feature. > > > > The cpufreq_table can be ordered and accessed in several ways which brings > > many combinations that would need to be supported, ending-up with something > > much more intrusive. (We can though decide to limit the feature to the low to > > high access that schedutil needs). > > > > As the EM needs schedutil to exist anyway, it seemed to be the right place for > > this code. It allows any cpufreq driver to benefit from the feature, simplify a > > potential extension for a usage by devfreq devices and as a bonus it speeds-up > > energy computing, allowing a more complex Energy Model. > > I was thinking of something a bit simpler. cpufreq_driver_resolve_freq > appears to be used only from schedutil (why is it even then?), so we > could just pull it into cpufreq_schedutil.c and just plain skip the call > to cpufreq_frequency_table_target if the target freq has been indexed in > the EM table -- it should already be matching a real OPP. > > Thoughts? > Quentin Can try that for a V2. That means em_pd_get_efficient_freq() would have to know about policy clamping (but I don't think that's an issue) and probably we still have to do the frequency resolution if the driver declared the resolve_freq callback? -- Vincent