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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 1D926C433DF for ; Wed, 27 May 2020 15:02:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0645A20899 for ; Wed, 27 May 2020 15:02:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389427AbgE0PCq (ORCPT ); Wed, 27 May 2020 11:02:46 -0400 Received: from foss.arm.com ([217.140.110.172]:39702 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389400AbgE0PCp (ORCPT ); Wed, 27 May 2020 11:02:45 -0400 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 BC9AB30E; Wed, 27 May 2020 08:02:44 -0700 (PDT) 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 A25323F52E; Wed, 27 May 2020 08:02:42 -0700 (PDT) References: <20200526151619.8779-1-benjamin.gaignard@st.com> <099f5b6c-aa81-be4a-19bf-52a2fff7b3db@st.com> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Benjamin GAIGNARD Cc: "rjw\@rjwysocki.net" , "viresh.kumar\@linaro.org" , Hugues FRUCHET , "mchehab\@kernel.org" , "mcoquelin.stm32\@gmail.com" , Alexandre TORGUE , "pavel\@ucw.cz" , "len.brown\@intel.com" , "vincent.guittot\@linaro.org" , "linux-pm\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "linux-media\@vger.kernel.org" , "linux-stm32\@st-md-mailman.stormreply.com" , "linux-arm-kernel\@lists.infradead.org" Subject: Re: [RFC RESEND 0/3] Introduce cpufreq minimum load QoS In-reply-to: <099f5b6c-aa81-be4a-19bf-52a2fff7b3db@st.com> Date: Wed, 27 May 2020 16:02:37 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 27/05/20 14:11, Benjamin GAIGNARD wrote: > On 5/27/20 2:14 PM, Valentin Schneider wrote: >> On 27/05/20 12:17, Benjamin GAIGNARD wrote: >>> On 5/27/20 12:09 PM, Valentin Schneider wrote: >>>> Hi Benjamin, >>>> >>>> On 26/05/20 16:16, Benjamin Gaignard wrote: >>>>> A first round [1] of discussions and suggestions have already be done on >>>>> this series but without found a solution to the problem. I resend it to >>>>> progress on this topic. >>>>> >>>> Apologies for sleeping on that previous thread. >>>> >>>> So what had been suggested over there was to use uclamp to boost the >>>> frequency of the handling thread; however if you use threaded IRQs you >>>> get RT threads, which already get the max frequency by default (at least >>>> with schedutil). >>>> >>>> Does that not work for you, and if so, why? >>> That doesn't work because almost everything is done by the hardware blocks >>> without charge the CPU so the thread isn't running. >> I'm not sure I follow; the frequency of the CPU doesn't matter while >> your hardware blocks are spinning, right? AIUI what matters is running >> your interrupt handler / action at max freq, which you get if you use >> threaded IRQs and schedutil. > Yes but not limited to schedutil. > Given the latency needed to change of frequencies I think it could > already too late > to change the CPU frequency when handling the threaded interrupt. Right, on my Juno the transition latency (i.e. worse case) is about 1.2ms; I can see that eating into your time budget, depending on the framerate you're going for. Vincent's got a point, if you can limit that max-freq-hold to a single frequency domain, that would probably be a tad better. Thanks for persisting through my questioning :-) >> >> I think it would help if you could clarify which tasks / parts of your >> pipeline you need running at high frequencies. The point is that setting >> a QoS request affects all tasks, whereas we could be smarter and only >> boost the required tasks. > What make us drop frames is that the threaded IRQ is scheduled too late. > The not thread part of the interrupt handler where we clear the > interrupt flags > is going fine but the thread part not. >> >>> I have done the >>> tests with schedutil >>> and ondemand scheduler (which is the one I'm targeting). I have no >>> issues when using >>> performance scheduler because it always keep the highest frequencies. >>> >>> >>>>> When start streaming from the sensor the CPU load could remain very low >>>>> because almost all the capture pipeline is done in hardware (i.e. without >>>>> using the CPU) and let believe to cpufreq governor that it could use lower >>>>> frequencies. If the governor decides to use a too low frequency that >>>>> becomes a problem when we need to acknowledge the interrupt during the >>>>> blanking time. >>>>> The delay to ack the interrupt and perform all the other actions before >>>>> the next frame is very short and doesn't allow to the cpufreq governor to >>>>> provide the required burst of power. That led to drop the half of the frames. >>>>> >>>>> To avoid this problem, DCMI driver informs the cpufreq governors by adding >>>>> a cpufreq minimum load QoS resquest. >>>>> >>>>> Benjamin >>>>> >>>>> [1] https://lkml.org/lkml/2020/4/24/360 >>>>> >>>>> Benjamin Gaignard (3): >>>>> PM: QoS: Introduce cpufreq minimum load QoS >>>>> cpufreq: governor: Use minimum load QoS >>>>> media: stm32-dcmi: Inform cpufreq governors about cpu load needs >>>>> >>>>> drivers/cpufreq/cpufreq_governor.c | 5 + >>>>> drivers/media/platform/stm32/stm32-dcmi.c | 8 ++ >>>>> include/linux/pm_qos.h | 12 ++ >>>>> kernel/power/qos.c | 213 ++++++++++++++++++++++++++++++ >>>>> 4 files changed, 238 insertions(+)