From: Juri Lelli <juri.lelli@gmail.com>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Leo Yan <leo.yan@linaro.org>,
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 <viresh.kumar@linaro.org>
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 [thread overview]
Message-ID: <20180327130808.GE10639@localhost.localdomain> (raw)
In-Reply-To: <719e1d94-170c-f208-d4a2-f3e882b1e20e@linaro.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
next prev parent reply other threads:[~2018-03-27 13:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1519226968-19821-1-git-send-email-daniel.lezcano@linaro.org>
[not found] ` <1519226968-19821-6-git-send-email-daniel.lezcano@linaro.org>
2018-03-06 23:19 ` [PATCH V2 5/7] thermal/drivers/cpu_cooling: Add idle cooling device documentation Pavel Machek
2018-03-07 11:42 ` Daniel Lezcano
2018-03-08 8:59 ` Pavel Machek
2018-03-08 11:54 ` Daniel Thompson
2018-03-07 17:09 ` [PATCH V2 0/7] CPU cooling device new strategies Eduardo Valentin
2018-03-07 18:57 ` Daniel Lezcano
2018-03-08 12:03 ` Daniel Thompson
2018-03-26 14:30 ` Leo Yan
2018-03-27 9:35 ` Daniel Lezcano
[not found] ` <1519226968-19821-7-git-send-email-daniel.lezcano@linaro.org>
[not found] ` <20180223073432.GF26947@vireshk-i7>
[not found] ` <faaf027c-e01c-6801-9a0c-ab7e0ba669a1@linaro.org>
2018-02-26 4:30 ` [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver Viresh Kumar
2018-03-13 19:15 ` Daniel Lezcano
2018-04-04 8:50 ` Daniel Lezcano
2018-04-05 4:49 ` Viresh Kumar
2018-03-27 3:43 ` Leo Yan
2018-03-27 11:10 ` Daniel Lezcano
2018-03-27 2:03 ` Leo Yan
2018-03-27 10:26 ` Daniel Lezcano
2018-03-27 12:28 ` Juri Lelli
2018-03-27 12:31 ` Daniel Lezcano
2018-03-27 13:08 ` Juri Lelli [this message]
2018-03-27 3:35 ` Leo Yan
2018-03-27 10:56 ` Daniel Lezcano
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