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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 F212FC388F7 for ; Thu, 22 Oct 2020 16:29:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8EF392463F for ; Thu, 22 Oct 2020 16:29:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2901785AbgJVQ3s (ORCPT ); Thu, 22 Oct 2020 12:29:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:50076 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2901774AbgJVQ3s (ORCPT ); Thu, 22 Oct 2020 12:29:48 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D823AAC48; Thu, 22 Oct 2020 16:29:46 +0000 (UTC) Date: Thu, 22 Oct 2020 17:29:43 +0100 From: Mel Gorman To: Peter Zijlstra Cc: "Rafael J. Wysocki" , Giovanni Gherdovich , Viresh Kumar , Julia Lawall , 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 , srinivas.pandruvada@linux.intel.com, Linux PM , Len Brown Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core Message-ID: <20201022162943.GL32041@suse.de> References: <1603211879-1064-1-git-send-email-Julia.Lawall@inria.fr> <34115486.YmRjPRKJaA@kreacher> <20201022120213.GG2611@hirez.programming.kicks-ass.net> <1790766.jaFeG3T87Z@kreacher> <20201022122949.GW2628@hirez.programming.kicks-ass.net> <20201022145250.GK32041@suse.de> <20201022152514.GJ2611@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20201022152514.GJ2611@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 22, 2020 at 05:25:14PM +0200, Peter Zijlstra wrote: > On Thu, Oct 22, 2020 at 03:52:50PM +0100, Mel Gorman wrote: > > > There are some questions > > currently on whether schedutil is good enough when HWP is not available. > > Srinivas and Rafael will know better, but Intel does run a lot of tests > and IIRC it was found that schedutil was on-par for !HWP. That was the > basis for commit: > > 33aa46f252c7 ("cpufreq: intel_pstate: Use passive mode by default without HWP") > > But now it turns out that commit results in running intel_pstate-passive > on ondemand, which is quite horrible. > I know Intel ran a lot of tests, no question about it and no fingers are being pointed. I know I've had enough bugs patches tested with a battery of tests on various machines and still ended up with bug reports :) > > There was some evidence (I don't have the data, Giovanni was looking into > > it) that HWP was a requirement to make schedutil work well. > > That seems to be the question; Rafael just said the opposite. > > > For distros, switching to schedutil by default would be nice because > > frequency selection state would follow the task instead of being per-cpu > > and we could stop worrying about different HWP implementations but it's > > s/HWP/cpufreq-governors/ ? But yes. > I've seen cases where HWP had variable behaviour between CPU generations. It was hard to quantify and/or figure out because HWP is a black box. > > not at the point where the switch is advisable. I would expect hard data > > before switching the default and still would strongly advise having a > > period of time where we can fall back when someone inevitably finds a > > new corner case or exception. > > Which is why I advocated to make it 'difficult' to use the old ones and > only later remove them. > That's fair. -- Mel Gorman SUSE Labs