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=-5.3 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 37F9EC433E0 for ; Fri, 19 Feb 2021 09:45:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E4E1D64EC0 for ; Fri, 19 Feb 2021 09:45:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230152AbhBSJpl (ORCPT ); Fri, 19 Feb 2021 04:45:41 -0500 Received: from foss.arm.com ([217.140.110.172]:60446 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229766AbhBSJp3 (ORCPT ); Fri, 19 Feb 2021 04:45:29 -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 CA595D6E; Fri, 19 Feb 2021 01:44:42 -0800 (PST) Received: from localhost (unknown [10.1.195.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 686C13F694; Fri, 19 Feb 2021 01:44:42 -0800 (PST) Date: Fri, 19 Feb 2021 09:44:40 +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: <20210219094440.GA29843@arm.com> References: <20210203114521.GA6380@arm.com> <20210205091424.3od3tme3f7mh7ebp@vireshk-i7> <20210217002422.GA17422@arm.com> <20210218093304.3mt3o7kbeymn5ofl@vireshk-i7> <20210218163635.GA23622@arm.com> <20210219045823.beeijwaymd63prk7@vireshk-i7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210219045823.beeijwaymd63prk7@vireshk-i7> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 19 Feb 2021 at 10:28:23 (+0530), Viresh Kumar wrote: > On 18-02-21, 16:36, Ionela Voinescu wrote: > > Yes, we don't care if there is no cpufreq driver, as the use of AMUs won't > > get initialised either. But we do care if there is a cpufreq driver that > > does not support frequency invariance, which is the example above. > > > > The intention with the patches that made cpufreq based invariance generic > > a while back was for it to be present, seamlessly, for as many drivers as > > possible, as a less than accurate invariance default method is still > > better than nothing. > > Right. > > > So only a few drivers today don't support cpufreq based FI > > Only two AFAICT, both x86, and the AMU stuff doesn't conflict with > them. > > drivers/cpufreq/intel_pstate.c > drivers/cpufreq/longrun.c > > > but it's not a guarantee that it will stay this way. > > What do you mean by "no guarantee" here ? > > The very core routines (cpufreq_freq_transition_end() and > cpufreq_driver_fast_switch()) of the cpufreq core call > arch_set_freq_scale() today and this isn't going to change anytime > soon. If something gets changed there someone will need to see other > parts of the kernel which may get broken with that. > Yes, but it won't really be straightforward to notice this breakage if that happens, so in my opinion it was worth to keep that condition. > I don't see any need of complicating other parts of the kernel like, > amu or cppc code for that. They should be kept simple and they should > assume cpufreq invariance will be supported as it is today. > Fair enough! It is a corner case after all. Thanks, Ionela. > -- > viresh