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

[Lukasz Luba]

Hi Krzysztof,

On 1/31/20 8:41 PM, Krzysztof Kozlowski wrote:
> On Fri, Jan 31, 2020 at 05:30:46PM +0000, Lukasz Luba wrote:
>   
> > > >                   |-----------------------------------------------|---------------
> > > >                   | 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.
>
> Mhmm... I was not specific - I mean, "performance governor". All this
> you mentioned should not differ between performance governor before and
> after. However once you have 12.7, then 13.0 - 12.2. Unless multi-core
> scheduler affects it... but then these numbers here are not showing
> only this change, but also the SCHED_MC effect.  In such case each of
> commits should be coming with their own numbers.

Agree, I should have not put 'this patch set' in the commit
msg. It should go into the cover letter and avoid this confusion.
You are right with ' Unless multi-core scheduler affects it...',
that's why when the SCHED_MC is missing, the decisions about task
placing might cause this variation and delay '13.0 - 12.2' seconds.

> > 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.
>
> I understand now that their independent. Still, they are part of one
> goal to tune the scheduler for Exynos platform. Splitting these looks
> too much, like enabling multiple drivers one after another.
>
> However if you provide numbers for each of cases (before patches, multi
> core scheduler, energy model with DTS), then I see benefit of splitting
> it.  Each commit would have its own rationale.  I am not sure if it is
> worth such investigation - that's just defconfig... distros might ignore
> it anyway.

Good point, and I agree that it would require more investigation, for
which unfortunately I don't have currently spare cycles.

Should I merge patch 1/3 and 3/3 and send the v2 with a cover letter
which would have the test results?

Regards,
Lukasz