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

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Message-ID: <20230515191827.m57e5raraoqbmer3@airbuntu>
Date:   Mon, 15 May 2023 20:18:27 +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 05/11/23 17:25, Dietmar Eggemann wrote:
> On 04/05/2023 17:23, Qais Yousef wrote:
> > 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:
> 
> [...]
> 
> >>> 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. 
> 
> I contacted MTK beginning of March this year and specifically asked them
> to see whether this patch helps their gaming use-cases or not.
> Unfortunately I haven't heard back from them.

Hmm I'm not sure if gfxbench would be benchmark to try to help here..

> 
> I'm actually happy to have compelling Jankbench (which _the_ UI

I'm glad you're getting these good numbers. But I am still worried this is
might not be sufficient. My worry here is how this could impact thermal and
power in all other cases. You're assuming any contention is worth a boost.

> benchmark app) numbers on a recent mobile device (Pixel6) with v5.18
> mainline based kernel including schedutil. And I'm able to remove a lot
> of extra product-oriented features, like up/down frequency transition
> rate-limits or ADPF (Android Dynamic Performance Framework) 'CPU
> performance hints' feature. Bridging product and mainline world for
> mobile isn't easy as we all know.
> 
> ---
> 
> Testcase is Jankbench (all subtests, 10 iterations) on Pixel6 (Android
> 12) with mainline v5.18 kernel and forward ported task scheduler
> patches, uclamp has been deactivated to disable ADPF's 'CPU performance
> hints'.
> 
> Max_frame_duration:
> +-----------------+------------+
> |     kernel      | value [ms] |
> +-----------------+------------+
> |      base       | 163.061513 |
> |    runnable     | 157.821346 |
> +-----------------+------------+
> 
> Mean_frame_duration:
> +-----------------+------------+----------+
> |     kernel      | value [ms] | diff [%] |
> +-----------------+------------+----------+
> |      base       |    18.0    |    0.0   |
> |    runnable     |    12.5    |  -30.64  |
> +-----------------+------------+----------+
> 
> Jank percentage (Jank deadline 16ms):
> +-----------------+------------+----------+
> |     kernel      | value [%]  | diff [%] |
> +-----------------+------------+----------+
> |      base       |     3.6    |    0.0   |
> |    runnable     |     0.8    |  -76.59  |
> +-----------------+------------+----------+
> 
> Power usage [mW] (total - all CPUs):
> +-----------------+------------+----------+
> |     kernel      | value [mW] | diff [%] |
> +-----------------+------------+----------+
> |      base       |    129.5   |    0.0   |
> |    runnable     |    129.3   |   -0.15  |
> +-----------------+------------+----------+
> 
> ---
> 
> I assume that the MTK folks will also profit from the fact that CPU
> frequency can ramp up faster with this 'runnable boosting', especially
> when activity starts from an (almost) idle little CPU. Seeing their test
> results here would be nice though.

My worry is that this is another optimization for performance first with
disregard to potential bad power and thermal impact.

> 
> 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.
> 
> This is the stalled discussion under
> https://lkml.kernel.org/r/20230205224318.2035646-1-qyousef@layalina.io I
> assume?
> 
> IIRC, the open question was should EAS CPU selection be performed in
> case there is no CPU spare capacity (due to uclamp capping) left.
> 
> [...]
> 
>