Messages in this thread | | | Date | Tue, 27 Mar 2018 15:08:08 +0200 | From | Juri Lelli <> | Subject | Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver |
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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
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