Re: [PATCH 3/3] ARM: exynos_defconfig: Enable Energy Model framework

[Lukasz Luba]

Hi Krzysztof,

On 1/31/20 1:16 PM, Krzysztof Kozlowski wrote:
> On Mon, 27 Jan 2020 at 22:55, <lukasz.luba@xxxxxxx> wrote:
> > From: Lukasz Luba <lukasz.luba@xxxxxxx>
> >
> > Enable the Energy Model (EM) brings possibility to use Energy Aware
> > Scheduler (EAS). This compiles the EM but does not enable to run EAS in
> > default. The EAS only works with SchedUtil - a CPUFreq governor which
> > handles direct requests from the scheduler for the frequency change. Thus,
> > to make EAS working in default, the SchedUtil governor should be
> > configured as default CPUFreq governor.
>
> Full stop. That's enough of needed explanation of schedutil.

OK

> > Although, the EAS might be enabled
> > in runtime, when the EM is present for CPUs, the SchedUtil is compiled and
> > then set as CPUFreq governor, i.e.:
> >
> > echo schedutil > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> > echo schedutil > /sys/devices/system/cpu/cpu4/cpufreq/scaling_governor
> >
> > To check if EAS is ready to work, the read output from the command below
> > should show '1':
> > cat /proc/sys/kernel/sched_energy_aware
> >
> > To disable EAS in runtime simply 'echo 0' to the file above.
>
> Not related to this commit. If you were implemeting here
> schedutil/EAS, then it makes sense to post all this. However what's
> the point to describe it in every defconfig change?

I will drop it.

> > Some test results, which stress the scheduler on Odroid-XU3:
> > hackbench -l 500 -s 4096
> > With mainline code and with this patch set.
>
> Skip the last sentence - duplicated information.

OK

> > The tests have been made with and without CONFIG_PROVE_LOCKING (PL)
> > (which is set to =y in default exynos_defconfig)
> >
> >                  |               this patch set                  | mainline
>
> The commit will be applied on its own branch so the meaning of "this
> patch set" will be lost. Maybe just "before/after"?

OK

> >                  |-----------------------------------------------|---------------
> >                  | performance   | SchedUtil     | SchedUtil     | performance
> >                  | governor      | governor      | governor      | governor
> >                  |               | w/o EAS       | w/ EAS        |
> > ----------------|---------------|---------------|---------------|---------------
> > hackbench w/ PL | 12.7s         | 11.7s         | 12.0s         | 13.0s - 12.2s
> > hackbench w/o PL| 9.2s          | 8.1s          | 8.2s          | 9.2s - 8.4s
>
> Why does the performance different before and after this patch?

Probably due to better locality and cache utilization. I can see that
there is ~700k context switches vs ~450k and ~160k migrations vs ~50k.
If you need to communicate two threads in different clusters, it will go
through CCI.

> Mention - lower better (?). Space between number and unit... or better
> mention [s] in column title.

OK

> And last but not least:
> Why this patch is separate from 1/3? I don't get the need of splitting them.

As mentioned in response to patch 1/3. The fist patch would create MC
domain, something different than Energy Model or EAS. The decisions in
the scheduler would be different.

I can merge 1/3 and 3/3 if you like, though.

Regards,
Lukasz

> Best regards,
> Krzysztof