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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 6183AC433E0 for ; Mon, 25 Jan 2021 18:15:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 156A622B3F for ; Mon, 25 Jan 2021 18:15:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731367AbhAYSOu (ORCPT ); Mon, 25 Jan 2021 13:14:50 -0500 Received: from foss.arm.com ([217.140.110.172]:54048 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731296AbhAYRyn (ORCPT ); Mon, 25 Jan 2021 12:54:43 -0500 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 A29DA1063; Mon, 25 Jan 2021 09:53:57 -0800 (PST) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6845F3F66E; Mon, 25 Jan 2021 09:53:55 -0800 (PST) Subject: Re: [PATCH] sched/fair: Rate limit calls to update_blocked_averages() for NOHZ To: Vincent Guittot Cc: Joel Fernandes , linux-kernel , Paul McKenney , Frederic Weisbecker , Qais Yousef , Ben Segall , Daniel Bristot de Oliveira , Ingo Molnar , Juri Lelli , Mel Gorman , Peter Zijlstra , Steven Rostedt References: <20210122154600.1722680-1-joel@joelfernandes.org> <2cd5683f-eea3-e661-7dd0-c617c836896f@arm.com> From: Dietmar Eggemann Message-ID: <8db5ebd3-4e5c-cd7e-e0cb-dc86c3cafb5c@arm.com> Date: Mon, 25 Jan 2021 18:53:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/01/2021 18:30, Vincent Guittot wrote: > On Mon, 25 Jan 2021 at 11:45, Dietmar Eggemann wrote: >> >> On 22/01/2021 20:10, Joel Fernandes wrote: >>> Hi Vincent, >>> >>> Thanks for reply. Please see the replies below: >>> >>> On Fri, Jan 22, 2021 at 05:56:22PM +0100, Vincent Guittot wrote: >>>> On Fri, 22 Jan 2021 at 16:46, Joel Fernandes (Google) >>>> wrote: [...] >> If I understood you correctly, you want to avoid these frequent calls >> to update_blocked_averages() here to further avoid invoking sched_util >> via update_blocked_averages() -> cpufreq_update_util() (since 'decayed' >> is set) very often in your setup. > > So It's not clear if the problem that joel wants to raise, is about: > - the running time of update_blocked_averages > - the running time of the cpufreq_update_util which is called because > utilization has decayed during the update of blocked load > - the wake up latency because of newly_idle lb Pretty much so. IIRC his interest is driven by the fact that he saw much less activity in newly_idle lb and therefore cpufreq_update_util on a system with the same kernel and userspace but with less CPUs (i.e. also smaller frequency domains) and less cgroups (with blocked load) and started wondering why. I assume that since he understands this environment now much better, he should be able to come up with better test numbers to show if there is a performance issue on his 2+6 DynamIQ system and if yes, where exactly in this code path.