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 9EC16C432C3 for ; Wed, 27 Nov 2019 14:58:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A2DD2080F for ; Wed, 27 Nov 2019 14:58:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726558AbfK0O6z (ORCPT ); Wed, 27 Nov 2019 09:58:55 -0500 Received: from foss.arm.com ([217.140.110.172]:48630 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726537AbfK0O6z (ORCPT ); Wed, 27 Nov 2019 09:58:55 -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 A22E430E; Wed, 27 Nov 2019 06:58:52 -0800 (PST) Received: from [192.168.0.9] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 268D63F68E; Wed, 27 Nov 2019 06:58:51 -0800 (PST) Subject: Re: [PATCH] cpufreq: vexpress-spc: Fix wrong alternation of policy->related_cpus during CPU hp To: Sudeep Holla , Viresh Kumar Cc: "Rafael J . Wysocki" , Liviu Dudau , Lorenzo Pieralisi , Morten Rasmussen , Lukasz Luba , linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20191127114801.23837-1-dietmar.eggemann@arm.com> <20191127120816.GC29301@bogus> <20191127121402.vd3tul4gmqm6qtyb@vireshk-i7> <20191127133200.GE29301@bogus> From: Dietmar Eggemann Message-ID: Date: Wed, 27 Nov 2019 15:58:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: <20191127133200.GE29301@bogus> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 27/11/2019 14:32, Sudeep Holla wrote: > On Wed, Nov 27, 2019 at 05:44:02PM +0530, Viresh Kumar wrote: >> On 27-11-19, 12:08, Sudeep Holla wrote: >>> On Wed, Nov 27, 2019 at 12:48:01PM +0100, Dietmar Eggemann wrote: [...] >>> Unlike DT based drivers, it not easy to get the fixed cpumask unless we >>> add some mechanism to extract it based on clks/OPP added. I prefer >>> this simple solution instead. >> >> I will call this a work-around for the problem and not really the >> solution, though I won't necessarily oppose it. There are cases which >> will break even with this solution. >> > > I agree and that's the reason I spoke out my thought aloud here :) > >> - Boot board with cpufreq driver as module. >> - Offline all CPUs except CPU0. >> - insert cpufreq driver. >> - online all CPUs. >> > > Indeed, not just boot anytime since it's a module :) > >> Now there is no guarantee that the last online will get the mask >> properly, if I have understood the problem well :) >> > > Yes > >> But yeah, who does this kind of messy work anyway :) >> > > I won't bet on that ;) > >> FWIW, we need a proper way (may be from architecture code) to find >> list of all CPUs that share clock line. >> > > Yes but there's no architectural way. I need to revise and see tc2_pm.c > to check if we can do any magic there. I'm fine with finding a better solution to return a fixed topology core cpumask or calling this patch a workaround. AFAICS, only TC2 is affected. ("arm: Fix topology setup in case of CPU hotplug for CONFIG_SCHED_MC") is needed for other systems as well in case we have commit ca74b316df96 ("arm: Use common cpu_topology structure and functions."). We probably don't want to revert commit ca74b316df96? We do CPU hp stress tests in our EAS mainline integration test suite https://developer.arm.com/tools-and-software/open-source-software/linux-kernel/energy-aware-scheduling/eas-mainline-development and there is where we initially encountered this issue on TC2.