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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 61599C433F5 for ; Wed, 9 Mar 2022 15:37:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232166AbiCIPiy (ORCPT ); Wed, 9 Mar 2022 10:38:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52408 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229796AbiCIPix (ORCPT ); Wed, 9 Mar 2022 10:38:53 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 19D272191; Wed, 9 Mar 2022 07:37:52 -0800 (PST) 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 C04111688; Wed, 9 Mar 2022 07:37:51 -0800 (PST) Received: from localhost (ionvoi01-desktop.cambridge.arm.com [10.1.196.65]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 644153F7F5; Wed, 9 Mar 2022 07:37:51 -0800 (PST) Date: Wed, 9 Mar 2022 15:37:49 +0000 From: Ionela Voinescu To: Yicong Yang Cc: Sudeep Holla , "Rafael J . Wysocki" , Thomas Gleixner , Ingo Molnar , Giovanni Gherdovich , Catalin Marinas , Will Deacon , Valentin Schneider , Dietmar Eggemann , Sean Kelley , yangyicong@hisilicon.com, Pierre Gondois , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 2/3] arch_topology: obtain cpu capacity using information from CPPC Message-ID: References: <20220302180913.13229-1-ionela.voinescu@arm.com> <20220302180913.13229-3-ionela.voinescu@arm.com> <4283eacf-6eab-b2f5-07f2-d19fad134277@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4283eacf-6eab-b2f5-07f2-d19fad134277@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Hi Yicong, On Wednesday 09 Mar 2022 at 18:21:30 (+0800), Yicong Yang wrote: > Hi Ionela, > > On 2022/3/3 2:09, Ionela Voinescu wrote: > > Define topology_init_cpu_capacity_cppc() to use highest performance > > values from _CPC objects to obtain and set maximum capacity information > > for each CPU. acpi_cppc_processor_probe() is a good point at which to > > trigger the initialization of CPU (u-arch) capacity values, as at this > > point the highest performance values can be obtained from each CPU's > > _CPC objects. Architectures can therefore use this functionality > > through arch_init_invariance_cppc(). > > > > The performance scale used by CPPC is a unified scale for all CPUs in > > the system. Therefore, by obtaining the raw highest performance values > > from the _CPC objects, and normalizing them on the [0, 1024] capacity > > scale, used by the task scheduler, we obtain the CPU capacity of each > > CPU. > > > > So we're going to use highest performance rather than nominal performance, > and I checked the discussion in v2 [1]. Maybe we should also document this > in sched-capacity.rst that where scheduler get the capacity from on ACPI > based system? Currently we only have DT part but after this patch it's > also supported on ACPI based system. > It's a very good point. I'll send a separate patch for this with added information in "3.1 CPU capacity" in sched-capacity.rst. I'll send this separate and not with the rebase that Rafael requested to avoid confusing things. > Out of curiosity, since we have raw capacity now on ACPI system, seems we > are able to scale the capacity with freq_factor now? looked into > register_cpufreq_notifier(). > The freq_factor is only used for DT systems where one provides "capacity-dmips-mhz" in DT. This entry actually represents DMIPS/MHz. So the freq_factor, set to: per_cpu(freq_factor, cpu) = policy->cpuinfo.max_freq / 1000; is used to obtain the performance at the maximum frequency, basically DMIPS = (Dhrystone) million instructions per second, by multiplying this raw value from DT with the freq_factor. After this, all these value for each CPU type are normalized on a scale [0, 1024], resulting in what we call CPU capacity. For ACPI systems freq_factor will have the default value of 1 when we call topology_normalize_cpu_scale(), as the performance value obtained from _CPC is already representative for the highest frequency of the CPU and not performance/Hz as we get from DT. Therefore, we are not and should not use a freq_factor here. Hopefully I understood your question correctly. Thanks, Ionela. > [1] https://lore.kernel.org/lkml/Yh5OAsYVBWWko+CH@arm.com/ > > Thanks, > Yicong