From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juri Lelli Subject: Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver Date: Tue, 27 Mar 2018 15:08:08 +0200 Message-ID: <20180327130808.GE10639@localhost.localdomain> 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> <719e1d94-170c-f208-d4a2-f3e882b1e20e@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <719e1d94-170c-f208-d4a2-f3e882b1e20e@linaro.org> Sender: linux-kernel-owner@vger.kernel.org To: Daniel Lezcano 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 27/03/18 14:31, Daniel Lezcano wrote: > 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. We might yes. And also for the update_single cases, I guess. Best, - Juri