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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 A49B2C4360C for ; Fri, 4 Oct 2019 08:24:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7417C21848 for ; Fri, 4 Oct 2019 08:24:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730917AbfJDIYR (ORCPT ); Fri, 4 Oct 2019 04:24:17 -0400 Received: from mx2.suse.de ([195.135.220.15]:49644 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727721AbfJDIYR (ORCPT ); Fri, 4 Oct 2019 04:24:17 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 503B9AC8B; Fri, 4 Oct 2019 08:24:15 +0000 (UTC) Message-ID: <1570177786.30086.1.camel@suse.cz> Subject: Re: [PATCH v2 2/2] cpufreq: intel_pstate: Conditional frequency invariant accounting From: Giovanni Gherdovich To: Srinivas Pandruvada , "Rafael J. Wysocki" Cc: Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Borislav Petkov , Len Brown , x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Mel Gorman , Matt Fleming , Viresh Kumar , Juri Lelli , Paul Turner , Vincent Guittot , Quentin Perret , Dietmar Eggemann , Doug Smythies Date: Fri, 04 Oct 2019 10:29:46 +0200 In-Reply-To: <5d6d601d2647644238fc51621407061e1c29320d.camel@linux.intel.com> References: <20191002122926.385-1-ggherdovich@suse.cz> <20191002122926.385-3-ggherdovich@suse.cz> <13106850.QMtCbivBLn@kreacher> <5d6d601d2647644238fc51621407061e1c29320d.camel@linux.intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2019-10-03 at 20:31 -0700, Srinivas Pandruvada wrote: > On Thu, 2019-10-03 at 20:05 +0200, Rafael J. Wysocki wrote: > > On Wednesday, October 2, 2019 2:29:26 PM CEST Giovanni Gherdovich > > wrote: > > > From: Srinivas Pandruvada > > > > > > intel_pstate has two operating modes: active and passive. In "active" > > > mode, the in-built scaling governor is used and in "passive" mode, the > > > driver can be used with any governor like "schedutil". In "active" mode > > > the utilization values from schedutil is not used and there is a > > > requirement from high performance computing use cases, not to readas > > > well any APERF/MPERF MSRs. > > > > Well, this isn't quite convincing. > > > > In particular, I don't see why the "don't read APERF/MPERF MSRs" argument > > applies *only* to intel_pstate in the "active" mode. What about > > intel_pstate in the "passive" mode combined with the "performance" > > governor? Or any other governor different from "schedutil" for that > > matter? > > > > And what about acpi_cpufreq combined with any governor different from > > "schedutil"? > > > > Scale invariance is not really needed in all of those cases right now > > AFAICS, or is it? > > Correct. This is just part of the patch to disable in active mode > (particularly in HWP and performance mode). > > But this patch is 2 years old. The folks who wanted this, disable > intel-pstate and use userspace governor with acpi-cpufreq. So may be > better to address those cases too. I disagree with "scale invariance is needed only by the schedutil governor"; the two other users are the CPU's estimated utilization in the wakeup path, via cpu_util_without(), as well as the load-balance path, via cpu_util() which is used by update_sg_lb_stats(). Also remember that scale invariance is applied to both PELT signals util_avg and load_avg; schedutil uses the former but not the latter. I understand Srinivas patch to disable MSR accesses during the tick as a band-aid solution to address a specific use case he cares about, but I don't think that extending this approach to any non-schedutil governor is a good idea -- you'd be killing load balancing in the process. Giovanni