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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 95A18C4363A for ; Wed, 21 Oct 2020 18:18:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 438122242E for ; Wed, 21 Oct 2020 18:18:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2503977AbgJUSSg (ORCPT ); Wed, 21 Oct 2020 14:18:36 -0400 Received: from cloudserver094114.home.pl ([79.96.170.134]:54296 "EHLO cloudserver094114.home.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2443059AbgJUSSg (ORCPT ); Wed, 21 Oct 2020 14:18:36 -0400 X-Greylist: delayed 394 seconds by postgrey-1.27 at vger.kernel.org; Wed, 21 Oct 2020 14:18:35 EDT Received: from 89-77-60-66.dynamic.chello.pl (89.77.60.66) (HELO kreacher.localnet) by serwer1319399.home.pl (79.96.170.134) with SMTP (IdeaSmtpServer 0.83.491) id eea5634c258530cd; Wed, 21 Oct 2020 20:18:33 +0200 From: "Rafael J. Wysocki" To: Peter Zijlstra Cc: Julia Lawall , Mel Gorman , Ingo Molnar , kernel-janitors@vger.kernel.org, Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira , linux-kernel@vger.kernel.org, Valentin Schneider , Gilles Muller , viresh.kumar@linaro.org, srinivas.pandruvada@linux.intel.com Subject: Re: [PATCH] sched/fair: check for idle core Date: Wed, 21 Oct 2020 20:18:32 +0200 Message-ID: <2595824.rfLgtAVNJm@kreacher> In-Reply-To: <20201021125203.GG2628@hirez.programming.kicks-ass.net> References: <1603211879-1064-1-git-send-email-Julia.Lawall@inria.fr> <20201021125203.GG2628@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday, October 21, 2020 2:52:03 PM CEST Peter Zijlstra wrote: > On Wed, Oct 21, 2020 at 02:42:20PM +0200, Julia Lawall wrote: > > > > > > On Wed, 21 Oct 2020, Peter Zijlstra wrote: > > > > > On Wed, Oct 21, 2020 at 01:56:55PM +0200, Julia Lawall wrote: > > > > Prior to 5.8, my machine was using intel_pstate and had few background > > > > tasks. Thus the problem wasn't visible in practice. Starting with 5.8 > > > > the kernel decided that intel_cpufreq would be more appropriate, which > > > > introduced kworkers every 0.004 seconds on all cores. > > > > > > That still doesn't make any sense. Are you running the legacy on-demand > > > thing or something? > > > > > > Rafael, Srinivas, Viresh, how come it defaults to that? > > > > The relevant commits are 33aa46f252c7, and 39a188b88332 that fixes a small > > bug. I have a Intel(R) Xeon(R) CPU E7-8870 v4 @ 2.10GHz that does not > > have the HWP feature, even though the cores seemed to be able to change > > their frequencies at the hardware level. > > That just makes intel_pstate not prefer active mode. With the clear > intent that it should then go use schedutil, but somehow it looks like > you landed on ondemand, which is absolutely atrocious. Probably, the "default governor" setting was inherited from the old config. It didn't matter when the active mode was used by default, because it only recognizes the "powersave" and "performance" settings (and "ondemand" causes it to fall back to "powersave" IIRC). Cheers!