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Subject: Re: [PATCH v2 2/2] sched/cpufreq: Consider reduced CPU capacity in
 energy calculation
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Quentin Perret <qperret@google.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        vincent.donnefort@arm.com, Beata.Michalska@arm.com,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>, segall@google.com,
        Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>
References: <20210604080954.13915-1-lukasz.luba@arm.com>
 <20210604080954.13915-3-lukasz.luba@arm.com>
 <CAJZ5v0ji=601eHQzHP1KuiA_TRUBaeEL6=sSLR_sW12MS_8QcA@mail.gmail.com>
From:   Lukasz Luba <lukasz.luba@arm.com>
Message-ID: <6b10f1ed-17d7-e1b0-37c5-17ced9ba383c@arm.com>
Date:   Thu, 10 Jun 2021 09:19:08 +0100
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On 6/9/21 4:01 PM, Rafael J. Wysocki wrote:
> On Fri, Jun 4, 2021 at 10:10 AM Lukasz Luba <lukasz.luba@arm.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@arm.com>
> 
> For the schedutil part
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 


Thank you Rafael!

Regards,
Lukasz