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 405CAC5DF60 for ; Tue, 5 Nov 2019 21:29:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E717121929 for ; Tue, 5 Nov 2019 21:29:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729977AbfKEV3E (ORCPT ); Tue, 5 Nov 2019 16:29:04 -0500 Received: from foss.arm.com ([217.140.110.172]:54224 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729680AbfKEV3D (ORCPT ); Tue, 5 Nov 2019 16:29:03 -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 DE9D930E; Tue, 5 Nov 2019 13:29:02 -0800 (PST) Received: from localhost (e108754-lin.cambridge.arm.com [10.1.199.68]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7ED5C3F6C4; Tue, 5 Nov 2019 13:29:02 -0800 (PST) Date: Tue, 5 Nov 2019 21:29:01 +0000 From: Ionela Voinescu To: Thara Gopinath Cc: mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, rui.zhang@intel.com, edubezval@gmail.com, qperret@google.com, linux-kernel@vger.kernel.org, amit.kachhap@gmail.com, javi.merino@kernel.org, daniel.lezcano@linaro.org Subject: Re: [Patch v4 6/6] sched: thermal: Enable tuning of decay period Message-ID: <20191105212735.GA32353@e108754-lin> References: <1571776465-29763-1-git-send-email-thara.gopinath@linaro.org> <1571776465-29763-7-git-send-email-thara.gopinath@linaro.org> <20191104161035.GA6680@e108754-lin> <5DC1DADE.60603@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5DC1DADE.60603@linaro.org> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 05 Nov 2019 at 15:26:06 (-0500), Thara Gopinath wrote: > On 11/04/2019 11:12 AM, Ionela Voinescu wrote: > > Hi Thara, > > > > On Tuesday 22 Oct 2019 at 16:34:25 (-0400), Thara Gopinath wrote: > >> Thermal pressure follows pelt signas which means the > >> decay period for thermal pressure is the default pelt > >> decay period. Depending on soc charecteristics and thermal > >> activity, it might be beneficial to decay thermal pressure > >> slower, but still in-tune with the pelt signals. > > > > I wonder if it can be beneficial to decay thermal pressure faster as > > well. > > > > This implementation makes 32 (LOAD_AVG_PERIOD) the minimum half-life > > of the thermal pressure samples. This results in more than 100ms for a > > sample to decay significantly and therefore let's say it can take more > > than 100ms for capacity to return to (close to) max when the CPU is no > > longer capped. This value seems high to me considering that a minimum > > value should result in close to 'instantaneous' behaviour, when there > > are thermal capping mechanisms that can react in ~20ms (hikey960 has a > > polling delay of 25ms, if I'm remembering correctly). > > > > I agree 32ms seems like a good default but given that you've made this > > configurable as to give users options, I'm wondering if it would be > > better to cover a wider range. > > [...] > > Hi Ionela, > [...] > > Regarding a slower decay, we need a strong case for it. > > I think you mean faster decay, if you refer to my comment above. To be blunt, I'm not sure there is a strong case for either kind of dacay, if we look at the test results only. There is a theoretical case for both, in my opinion and given that the purpose of this patch is to give options to platform with different thermal characteristics, I do believe it's worth providing a good range of options for the decay period. Thanks, Ionela. > > -- > Warm Regards > Thara