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=-0.8 required=3.0 tests=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 60B9BC433E0 for ; Wed, 27 May 2020 12:14:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4241D208B6 for ; Wed, 27 May 2020 12:14:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728721AbgE0MOe (ORCPT ); Wed, 27 May 2020 08:14:34 -0400 Received: from foss.arm.com ([217.140.110.172]:37600 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725766AbgE0MOe (ORCPT ); Wed, 27 May 2020 08:14:34 -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 52F8755D; Wed, 27 May 2020 05:14:33 -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 3B21C3F305; Wed, 27 May 2020 05:14:31 -0700 (PDT) References: <20200526151619.8779-1-benjamin.gaignard@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: Date: Wed, 27 May 2020 13:14:24 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. > 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(+)