linux-kernel - Re: [PATCH v2 2/2] sched/cpufreq: Consider reduced CPU capacity in energy calculation

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Date:   Thu, 10 Jun 2021 09:19:08 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Quentin Perret <qperret@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        vincent.donnefort@....com, Beata.Michalska@....com,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>, segall@...gle.com,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v2 2/2] sched/cpufreq: Consider reduced CPU capacity in
 energy calculation



On 6/9/21 4:01 PM, Rafael J. Wysocki wrote:
> On Fri, Jun 4, 2021 at 10:10 AM Lukasz Luba <lukasz.luba@....com> wrote:
>>
>> Energy Aware Scheduling (EAS) needs to predict the decisions made by
>> SchedUtil. The map_util_freq() exists to do that.
>>
>> There are corner cases where the max allowed frequency might be reduced
>> (due to thermal). SchedUtil as a CPUFreq governor, is aware of that
>> but EAS is not. This patch aims to address it.
>>
>> SchedUtil stores the maximum allowed frequency in
>> 'sugov_policy::next_freq' field. EAS has to predict that value, which is
>> the real used frequency. That value is made after a call to
>> cpufreq_driver_resolve_freq() which clamps to the CPUFreq policy limits.
>> In the existing code EAS is not able to predict that real frequency.
>> This leads to energy estimation errors.
>>
>> To avoid wrong energy estimation in EAS (due to frequency miss prediction)
>> make sure that the step which calculates Performance Domain frequency,
>> is also aware of the allowed CPU capacity.
>>
>> Furthermore, modify map_util_freq() to not extend the frequency value.
>> Instead, use map_util_perf() to extend the util value in both places:
>> SchedUtil and EAS, but for EAS clamp it to max allowed CPU capacity.
>> In the end, we achieve the same desirable behavior for both subsystems
>> and alignment in regards to the real CPU frequency.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> 
> For the schedutil part
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 


Thank you Rafael!

Regards,
Lukasz