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

[Lukasz Luba]

On 6/9/21 4:01 PM, Rafael J. Wysocki wrote:
> On Fri, Jun 4, 2021 at 10:10 AM Lukasz Luba <lukasz.luba@xxxxxxx> 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@xxxxxxx>
>
> For the schedutil part
>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>


Thank you Rafael!

Regards,
Lukasz