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_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 465A9C2D0DB for ; Thu, 30 Jan 2020 15:33:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A82A2083E for ; Thu, 30 Jan 2020 15:33:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727368AbgA3Pda (ORCPT ); Thu, 30 Jan 2020 10:33:30 -0500 Received: from foss.arm.com ([217.140.110.172]:54476 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726948AbgA3Pd2 (ORCPT ); Thu, 30 Jan 2020 10:33:28 -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 838EB31B; Thu, 30 Jan 2020 07:33:27 -0800 (PST) Received: from localhost (unknown [10.1.198.81]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 24FC23F68E; Thu, 30 Jan 2020 07:33:27 -0800 (PST) Date: Thu, 30 Jan 2020 15:33:25 +0000 From: Ionela Voinescu To: Peter Zijlstra Cc: catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, maz@kernel.org, suzuki.poulose@arm.com, sudeep.holla@arm.com, dietmar.eggemann@arm.com, mingo@redhat.com, ggherdovich@suse.cz, vincent.guittot@linaro.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Juri Lelli Subject: Re: [PATCH v2 5/6] TEMP: sched: add interface for counter-based frequency invariance Message-ID: <20200130153325.GA5208@arm.com> References: <20191218182607.21607-1-ionela.voinescu@arm.com> <20191218182607.21607-6-ionela.voinescu@arm.com> <20200129193741.GU14914@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200129193741.GU14914@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 29 Jan 2020 at 20:37:41 (+0100), Peter Zijlstra wrote: > On Wed, Dec 18, 2019 at 06:26:06PM +0000, Ionela Voinescu wrote: > > To be noted that this patch is a temporary one. It introduces the > > interface added by the patches at [1] to allow update of the frequency > > invariance scale factor based on counters. If [1] is merged there is > > not need for this patch. > > > > For platforms that support counters (x86 - APERF/MPERF, arm64 - AMU > > counters) the frequency invariance correction factor can be obtained > > using a core counter and a fixed counter to get information on the > > performance (frequency based only) obtained in a period of time. This > > will more accurately reflect the actual current frequency of the CPU, > > compared with the alternative implementation that reflects the request > > of a performance level from the OS through the cpufreq framework > > (arch_set_freq_scale). > > > > Therefore, introduce an interface - arch_scale_freq_tick, to be > > implemented by each architecture and called for each CPU on the tick > > to update the scale factor based on the delta in the counter values, > > if counter support is present on the CPU. > > > > Either because reading counters is expensive or because reading > > counters from remote CPUs is not possible or is expensive, only > > update the counter based frequency scale factor on the tick for > > now. A tick based update will definitely be necessary either due to > > it being the only point of update for certain architectures or in > > order to cache the counter values for a particular CPU, if a > > further update from that CPU is not possible. > > > > [1] > > https://lore.kernel.org/lkml/20191113124654.18122-1-ggherdovich@suse.cz/ > > FWIW, those patches just landed in tip/sched/core Thanks, Peter, I'll drop this one next time around. Ionela.