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. -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog