linux-kernel - Re: [PATCH 1/1] sched: Consider CPU contention in frequency & load-balance busiest CPU selection

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Date:   Thu, 4 May 2023 16:23:28 +0100
From:   Qais Yousef <qyousef@...alina.io>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Kajetan Puchalski <kajetan.puchalski@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Vincent Donnefort <vdonnefort@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Abhijeet Dharmapurikar <adharmap@...cinc.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] sched: Consider CPU contention in frequency &
 load-balance busiest CPU selection

On 05/03/23 19:13, Dietmar Eggemann wrote:
> On 29/04/2023 16:58, Peter Zijlstra wrote:
> > On Thu, Apr 06, 2023 at 05:50:30PM +0200, Dietmar Eggemann wrote:
> >> Use new cpu_boosted_util_cfs() instead of cpu_util_cfs().
> >>
> >> The former returns max(util_avg, runnable_avg) capped by max CPU
> >> capacity. CPU contention is thereby considered through runnable_avg.
> >>
> >> The change in load-balance only affects migration type `migrate_util`.
> > 
> > But why, and how does it affect? That is, isn't this Changelog a wee bit
> > sparse?
> 
> Absolutely. 
> 
> I have compelling test data based on JankbenchX on Pixel6 for 
> sugov_get_util() case I will share with v2.

I am actually still concerned this is a global win. This higher contention can
potentially lead to higher power usage. Not every high contention worth
reacting to faster. The blanket 25% headroom in map_util_perf() is already
problematic. And Jankbench is not a true representative of a gaming workload
which is what started this whole discussion. It'd be good if mediatek can
confirm this helps their case. Or for us to find a way to run something more
representative. The original ask was to be selective about being more reactive
for specific scenarios/workloads. If we can't make this selective we need more
data it won't hurt general power consumption. I plan to help with that, but my
focus now is on other areas first, namely getting uclamp_max usable in
production.

Sorry for being cynical. I appreciate all the effort put so far to help find
a sensible solution.

Thanks!

--
Qais Yousef