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 0DBECC433E0 for ; Wed, 17 Feb 2021 11:59:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B75C86024A for ; Wed, 17 Feb 2021 11:59:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232392AbhBQL67 (ORCPT ); Wed, 17 Feb 2021 06:58:59 -0500 Received: from foss.arm.com ([217.140.110.172]:57400 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232111AbhBQL6P (ORCPT ); Wed, 17 Feb 2021 06:58:15 -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 854FB31B; Wed, 17 Feb 2021 03:57:28 -0800 (PST) Received: from localhost (unknown [10.1.195.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 24BD23F694; Wed, 17 Feb 2021 03:57:28 -0800 (PST) Date: Wed, 17 Feb 2021 11:57:26 +0000 From: Ionela Voinescu To: Viresh Kumar Cc: Rafael Wysocki , Catalin Marinas , Will Deacon , Vincent Guittot , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, Sudeep Holla , Greg Kroah-Hartman Subject: Re: [PATCH V3 1/2] topology: Allow multiple entities to provide sched_freq_tick() callback Message-ID: <20210217115726.GA25441@arm.com> References: <20210203114521.GA6380@arm.com> <20210205091424.3od3tme3f7mh7ebp@vireshk-i7> <20210217002422.GA17422@arm.com> <20210217042558.o4anjdkayzgqny55@vireshk-i7> <20210217113011.GA22176@arm.com> <20210217114027.ashqh67hrfk4hwib@vireshk-i7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210217114027.ashqh67hrfk4hwib@vireshk-i7> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 17 Feb 2021 at 17:10:27 (+0530), Viresh Kumar wrote: > On 17-02-21, 11:30, Ionela Voinescu wrote: > > The problem is not topology_scale_freq_invariant() but whether a scale > > factor is set for some CPUs. > > > > Scenario (test system above): > > - "AMUs" are only supported for [1-2], > > - cpufreq_supports_freq_invariance() -> false > > > > What should happen: > > - topology_scale_freq_invariant() -> false (passed) > > - all CPUs should have their freq_scale unmodified (1024) - (failed) > > because only 2 out of 6 CPUs have a method of setting a scale factor > > > > What does happen: > > - arch_set_freq_tick() -> topology_set_freq_tick() will set a scale > > factor for [1-2] based on AMUs. This should not happen. We will end > > up with invariant signals for bigs and signals that are not freq > > invariant for littles. > > Another case. cpufreq is included as a module and AMU is implemented > partially. > > - first time cpufreq driver is inserted, we set up everything and > freq_scale gets updated on ticks. > > - remove cpufreq driver, we are back in same situation. > Yes, but the littles (lacking AMUs) would have had a scale factor set through arch_set_freq_scale() which will correspond to the last frequency change through the cpufreq driver. When removing the driver, it's unlikely that the frequency of littles will change (no driver). - topology_scale_freq_invariant() will still return true. - littles would still have a scale factor set which is likely accurate - bigs will continue updating the scale factor through AMUs. See a very useful comment someone added recently :) : """ + /* + * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU + * counters don't have any dependency on cpufreq driver once we have + * initialized AMU support and enabled invariance. The AMU counters will + * keep on working just fine in the absence of the cpufreq driver, and + * for the CPUs for which there are no counters available, the last set + * value of freq_scale will remain valid as that is the frequency those + * CPUs are running at. + */ """ > We can't control it that way.. Or we add another call layer in middle > before the tick-handler gets called for AMU, which will check if we > are fully invariant or not ? > I would avoid additional work done on the tick, especially for a scenario which is unlikely. If you think this case is worth supporting, it might be best to do it at CPUFREQ_REMOVE_POLICY event. Thanks, Ionela. > -- > viresh