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,NICE_REPLY_A,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 5C232C55178 for ; Fri, 6 Nov 2020 10:38:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 10CA620702 for ; Fri, 6 Nov 2020 10:38:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727156AbgKFKiN (ORCPT ); Fri, 6 Nov 2020 05:38:13 -0500 Received: from foss.arm.com ([217.140.110.172]:34668 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727094AbgKFKh6 (ORCPT ); Fri, 6 Nov 2020 05:37:58 -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 B57BA147A; Fri, 6 Nov 2020 02:37:56 -0800 (PST) Received: from [10.57.14.85] (unknown [10.57.14.85]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6AE973F719; Fri, 6 Nov 2020 02:37:53 -0800 (PST) Subject: Re: [PATCH v3 3/3] [RFC] CPUFreq: Add support for cpu-perf-dependencies To: Viresh Kumar , Nicola Mazzucato Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, devicetree@vger.kernel.org, sudeep.holla@arm.com, rjw@rjwysocki.net, vireshk@kernel.org, robh+dt@kernel.org, sboyd@kernel.org, nm@ti.com, daniel.lezcano@linaro.org, morten.rasmussen@arm.com, chris.redpath@arm.com References: <20201102120115.29993-1-nicola.mazzucato@arm.com> <20201102120115.29993-4-nicola.mazzucato@arm.com> <20201106092020.za3oxg7gutzc3y2b@vireshk-i7> From: Lukasz Luba Message-ID: <0a334a73-45ef-58ff-7dfd-9df6f4ff290a@arm.com> Date: Fri, 6 Nov 2020 10:37:51 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20201106092020.za3oxg7gutzc3y2b@vireshk-i7> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Viresh, On 11/6/20 9:20 AM, Viresh Kumar wrote: > On 02-11-20, 12:01, Nicola Mazzucato wrote: >> This is a continuation of the previous v2, where we focused mostly on the >> dt binding. >> >> I am seeking some feedback/comments on the following two approaches. >> >> Intro: >> We have seen that in a system where performance control and hardware >> description do not match (i.e. per-cpu), we still need the information of >> how the v/f lines are shared among the cpus. We call this information >> "performance dependencies". >> We got this info through the opp-shared (the previous 2 patches aim for >> that). >> >> Problem: >> How do we share such info (retrieved from a cpufreq driver) to other >> consumers that rely on it? I have two proposals. > > I haven't really stop thinking about what and how we should solve > this, but I have few concerns first. > >> 2) drivers/thermal/cpufreq_cooling: Replace related_cpus with dependent_cpus > > I am not sure if I understand completely on how this is going to be > modified/work. > > The only use of related_cpus in the cooling driver is in the helper > cdev->get_requested_power(), where we need to find the total power > being consumed by devices controlled by the cooling device. Right ? > > Now the cooling devices today are very closely related to the cpufreq > policy, the registration function itself takes a cpufreq policy as an > argument. > > Consider that you have an octa-core platform and all the CPUs are > dependent on each other. With your suggested changes and hw control, > we will have different cpufreq policies for each CPU. And so we will > have a cooling device, cdev, for each CPU as well. When the IPA > governor calls cdev->get_requested_power(), why should we ever bother > to traverse the list of dependent_cpus and not related_cpus only ? > > Otherwise the same CPU will have its load contributed to the power of > 8 cooling devices. > Good question. How about a different interface for those cpufreq drivers? That new registration API would allow to specify the cpumask. Or rely on EM cpumask: em_span_cpus(em) Currently we have two ways to register cooling device: 1. when the cpufreq driver set a flag CPUFREQ_IS_COOLING_DEV, the core will register cooling device 2. cpufreq driver can explicitly call the registration function: cpufreq_cooling_register() with 'policy' as argument That would need substantial change to the cpufreq cooling code, from policy oriented to custom driver's cpumask (like EM registration). Regards, Lukasz