From: Valentin Schneider <valentin.schneider@arm.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Amit Daniel Kachhap <amit.kachhap@gmail.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Javi Merino <javi.merino@kernel.org>,
Zhang Rui <rui.zhang@intel.com>, Amit Kucheria <amitk@kernel.org>,
linux-kernel@vger.kernel.org, Quentin Perret <qperret@google.com>,
Lukasz Luba <lukasz.luba@arm.com>,
linux-pm@vger.kernel.org
Subject: Re: [PATCH V3 2/2] thermal: cpufreq_cooling: Reuse sched_cpu_util() for SMP platforms
Date: Tue, 01 Dec 2020 17:25:46 +0000 [thread overview]
Message-ID: <jhjzh2xtp45.mognet@arm.com> (raw)
In-Reply-To: <1fa9994395764ba19cfe6240d8b3c1ce390e8f82.1605770951.git.viresh.kumar@linaro.org>
Hi Viresh,
On 19/11/20 07:38, Viresh Kumar wrote:
> As can be clearly seen, the load and requested_power numbers are simply
> incorrect in the idle time based approach and the numbers collected from
> CPU's utilization are much closer to the reality.
>
PELT time-scaling can make the util signals behave strangely from an
external PoV. For instance, on a big.LITTLE system, the rq util of a LITTLE
CPU may suddenly drop if it was stuck on a too-low OPP for some time and
eventually reached the "right" OPP (i.e. got idle time).
Also, as Peter pointed out in [1], task migrations can easily confuse an
external observer that considers util to be "an image of the recent past".
This will need testing on asymmetric CPU capacity systems, IMO.
[1]: https://lore.kernel.org/r/20201120075527.GB2414@hirez.programming.kicks-ass.net
next prev parent reply other threads:[~2020-12-01 17:26 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 7:38 [PATCH V3 0/2] cpufreq_cooling: Get effective CPU utilization from scheduler Viresh Kumar
2020-11-19 7:38 ` [PATCH V3 1/2] sched/core: Rename and move schedutil_cpu_util() to core.c Viresh Kumar
2020-11-19 12:30 ` Rafael J. Wysocki
2020-11-23 10:04 ` Viresh Kumar
2020-11-23 10:29 ` Rafael J. Wysocki
2020-11-19 7:38 ` [PATCH V3 2/2] thermal: cpufreq_cooling: Reuse sched_cpu_util() for SMP platforms Viresh Kumar
2020-11-20 14:51 ` Lukasz Luba
2020-11-23 10:41 ` Viresh Kumar
2020-11-23 11:34 ` Lukasz Luba
2020-11-23 15:32 ` Lukasz Luba
2020-11-24 4:56 ` Viresh Kumar
2020-12-01 17:25 ` Valentin Schneider [this message]
2020-12-07 9:13 ` Viresh Kumar
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