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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A008BC64E7A for ; Tue, 1 Dec 2020 17:26:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 52FE82168B for ; Tue, 1 Dec 2020 17:26:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387998AbgLAR0f (ORCPT ); Tue, 1 Dec 2020 12:26:35 -0500 Received: from foss.arm.com ([217.140.110.172]:46826 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387494AbgLAR0f (ORCPT ); Tue, 1 Dec 2020 12:26:35 -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 F30D8101E; Tue, 1 Dec 2020 09:25:49 -0800 (PST) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 51BAA3F575; Tue, 1 Dec 2020 09:25:48 -0800 (PST) References: <1fa9994395764ba19cfe6240d8b3c1ce390e8f82.1605770951.git.viresh.kumar@linaro.org> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Viresh Kumar Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Amit Daniel Kachhap , Daniel Lezcano , Javi Merino , Zhang Rui , Amit Kucheria , linux-kernel@vger.kernel.org, Quentin Perret , Lukasz Luba , linux-pm@vger.kernel.org Subject: Re: [PATCH V3 2/2] thermal: cpufreq_cooling: Reuse sched_cpu_util() for SMP platforms In-reply-to: <1fa9994395764ba19cfe6240d8b3c1ce390e8f82.1605770951.git.viresh.kumar@linaro.org> Date: Tue, 01 Dec 2020 17:25:46 +0000 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Hi Viresh, On 19/11/20 07:38, Viresh Kumar wrote: > As can be clearly seen, the load and requested_power numbers are simply > incorrect in the idle time based approach and the numbers collected from > CPU's utilization are much closer to the reality. > PELT time-scaling can make the util signals behave strangely from an external PoV. For instance, on a big.LITTLE system, the rq util of a LITTLE CPU may suddenly drop if it was stuck on a too-low OPP for some time and eventually reached the "right" OPP (i.e. got idle time). Also, as Peter pointed out in [1], task migrations can easily confuse an external observer that considers util to be "an image of the recent past". This will need testing on asymmetric CPU capacity systems, IMO. [1]: https://lore.kernel.org/r/20201120075527.GB2414@hirez.programming.kicks-ass.net