From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver Date: Tue, 27 Mar 2018 14:31:56 +0200 Message-ID: <719e1d94-170c-f208-d4a2-f3e882b1e20e@linaro.org> References: <1519226968-19821-1-git-send-email-daniel.lezcano@linaro.org> <1519226968-19821-7-git-send-email-daniel.lezcano@linaro.org> <20180327020331.GA21693@leoy-ThinkPad-X240s> <8ee2cb0d-9afe-6626-0911-90ff6660bf8a@linaro.org> <20180327122836.GD10639@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20180327122836.GD10639@localhost.localdomain> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Juri Lelli Cc: Leo Yan , edubezval@gmail.com, kevin.wangtao@linaro.org, vincent.guittot@linaro.org, amit.kachhap@gmail.com, linux-kernel@vger.kernel.org, javi.merino@kernel.org, rui.zhang@intel.com, daniel.thompson@linaro.org, linux-pm@vger.kernel.org, Viresh Kumar List-Id: linux-pm@vger.kernel.org On 27/03/2018 14:28, Juri Lelli wrote: > Hi Daniel, > > On 27/03/18 12:26, Daniel Lezcano wrote: >> On 27/03/2018 04:03, Leo Yan wrote: >>> Hi Daniel, >>> >>> On Wed, Feb 21, 2018 at 04:29:27PM +0100, Daniel Lezcano wrote: >>>> The cpu idle cooling driver performs synchronized idle injection across all >>>> cpus belonging to the same cluster and offers a new method to cool down a SoC. >>>> >>>> Each cluster has its own idle cooling device, each core has its own idle >>>> injection thread, each idle injection thread uses play_idle to enter idle. In >>>> order to reach the deepest idle state, each cooling device has the idle >>>> injection threads synchronized together. >>>> >>>> It has some similarity with the intel power clamp driver but it is actually >>>> designed to work on the ARM architecture via the DT with a mathematical proof >>>> with the power model which comes with the Documentation. >>>> >>>> The idle injection cycle is fixed while the running cycle is variable. That >>>> allows to have control on the device reactivity for the user experience. At >>>> the mitigation point the idle threads are unparked, they play idle the >>>> specified amount of time and they schedule themselves. The last thread sets >>>> the next idle injection deadline and when the timer expires it wakes up all >>>> the threads which in turn play idle again. Meanwhile the running cycle is >>>> changed by set_cur_state. When the mitigation ends, the threads are parked. >>>> The algorithm is self adaptive, so there is no need to handle hotplugging. >>> >>> The idle injection threads are RT threads (FIFO) and I saw in >>> play_idle() set/clear flag PF_IDLE for it. Will these idle injection >>> threads utilization be accounted into RT utilization? >>> >>> If idle injection threads utilization is accounted as RT tasks >>> utilization, will this impact CPUFreq governor 'schedutil' for OPP >>> selection? >> >> Hi Leo, >> >> The idle injection task has a very low utilization when it is not in the >> play_idle function, basically it wakes up, sets a timer and play_idle(). >> >> Regarding the use case, the idle injection is the base brick for an >> combo cooling device with cpufreq + cpuidle. When the idle injection is >> used alone, it is because there is no cpufreq driver for the platform. >> If there is a cpufreq driver, then we should endup with the cpu cooling >> device where we have control of the OPP (and there is no idle injection >> threads) or the combo cooling device. >> >> Except I'm missing something, the idle injection threads won't impact >> the OPP selection. > > Mmm, they actually might. schedutil selects max OPP as soon as it sees > an RT thread. I fear these guys might generate unwanted spikes. Maybe > you can filter them out? Yes, absolutely. Leo pointed it also. We might want to change the check at: https://elixir.bootlin.com/linux/v4.16-rc7/source/kernel/sched/cpufreq_schedutil.c#L364 in order to ignore PF_IDLE tagged tasks. -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog