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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 C0CEDC43142 for ; Fri, 22 Jun 2018 07:59:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A91823E84 for ; Fri, 22 Jun 2018 07:59:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7A91823E84 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 S932885AbeFVH66 (ORCPT ); Fri, 22 Jun 2018 03:58:58 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:59314 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751085AbeFVH65 (ORCPT ); Fri, 22 Jun 2018 03:58:57 -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 47CE71435; Fri, 22 Jun 2018 00:58:57 -0700 (PDT) Received: from e108498-lin.cambridge.arm.com (e108498-lin.cambridge.arm.com [10.1.211.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DC0663F557; Fri, 22 Jun 2018 00:58:54 -0700 (PDT) Date: Fri, 22 Jun 2018 08:58:53 +0100 From: Quentin Perret To: Peter Zijlstra Cc: Vincent Guittot , mingo@kernel.org, linux-kernel@vger.kernel.org, rjw@rjwysocki.net, juri.lelli@redhat.com, dietmar.eggemann@arm.com, Morten.Rasmussen@arm.com, viresh.kumar@linaro.org, valentin.schneider@arm.com, patrick.bellasi@arm.com, joel@joelfernandes.org, daniel.lezcano@linaro.org, Ingo Molnar Subject: Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking Message-ID: <20180622075853.GC23168@e108498-lin.cambridge.arm.com> References: <1528459794-13066-1-git-send-email-vincent.guittot@linaro.org> <1528459794-13066-5-git-send-email-vincent.guittot@linaro.org> <20180621184524.GB27616@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180621184524.GB27616@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.8.3 (2017-05-23) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On Thursday 21 Jun 2018 at 20:45:24 (+0200), Peter Zijlstra wrote: > On Fri, Jun 08, 2018 at 02:09:47PM +0200, Vincent Guittot wrote: > > static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu) > > { > > struct rq *rq = cpu_rq(sg_cpu->cpu); > > + unsigned long util; > > > > if (rq->rt.rt_nr_running) > > return sg_cpu->max; > > > > + util = sg_cpu->util_dl; > > + util += sg_cpu->util_cfs; > > + util += sg_cpu->util_rt; > > + > > /* > > * Utilization required by DEADLINE must always be granted while, for > > * FAIR, we use blocked utilization of IDLE CPUs as a mechanism to > > @@ -197,7 +204,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu) > > * util_cfs + util_dl as requested freq. However, cpufreq is not yet > > * ready for such an interface. So, we only do the latter for now. > > */ > > - return min(sg_cpu->max, (sg_cpu->util_dl + sg_cpu->util_cfs)); > > + return min(sg_cpu->max, util); > > } > > So this (and the dl etc. equivalents) result in exactly the problems > complained about last time, no? > > What I proposed was something along the lines of: > > util = 1024 * sg_cpu->util_cfs; > util /= (1024 - (sg_cpu->util_rt + sg_cpu->util_dl + ...)); > > return min(sg_cpu->max, util + sg_cpu->bw_dl); > > Where we, instead of directly adding the various util signals. > > I now see an email from Quentin asking if these things are not in fact > the same, but no, they are not. The difference is that the above only > affects the CFS signal and will re-normalize the utilization of an > 'always' running task back to 1 by compensating for the stolen capacity. > > But it will not, like these here patches, affect the OPP selection of > other classes. If there is no CFS utilization (or very little), then the > renormalization will not matter, and the existing DL bandwidth > compuation will be unaffected. Right, thinking more carefully about this re-scaling, the two things are indeed not the same, but I'm still not sure if this is what we want. Say we have 50% of the capacity stolen by RT, and a 25% CFS task running. If we re-scale, we'll end up with a 50% request for CFS (util==512 for your code above). But if we want to see a little bit of idle time in the system, we should really request an OPP for 75%+ of capacity no ? Or am I missing something ? And also, I think Juri had concerns when we use the util_dl (as a PELT signal) for OPP selection since that kills the benefit of DL for long running DL tasks. Or can we assume that DL tasks with very long runtime/periods are a corner case we can ignore ? Thanks, Quentin