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 19:11:12 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Qais Yousef <qyousef@...alina.io>,
        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 03/05/2023 18:08, Vincent Guittot wrote:
> On Thu, 6 Apr 2023 at 17:50, Dietmar Eggemann <dietmar.eggemann@....com> 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`.
> 
> would be good to get some figures to show the benefit

Yes. Will add JankbenchX on Pixel6 for sugov_get_util() and `perf bench
sched messaging` on Ampere Altra with the next version.

>> Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
>> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
>> ---
>>  kernel/sched/cpufreq_schedutil.c |  3 ++-
>>  kernel/sched/fair.c              |  2 +-
>>  kernel/sched/sched.h             | 19 +++++++++++++++++++
>>  3 files changed, 22 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>> index e3211455b203..728b186cd367 100644
>> --- a/kernel/sched/cpufreq_schedutil.c
>> +++ b/kernel/sched/cpufreq_schedutil.c
>> @@ -158,7 +158,8 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu)
>>         struct rq *rq = cpu_rq(sg_cpu->cpu);
>>
>>         sg_cpu->bw_dl = cpu_bw_dl(rq);
>> -       sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu),
>> +       sg_cpu->util = effective_cpu_util(sg_cpu->cpu,
>> +                                         cpu_boosted_util_cfs(sg_cpu->cpu),
> 
> Shouldn't we have a similar change in feec to estimate correctly which
> OPP/ freq will be selected by schedutil ?

Yes, this should be more correct. Schedutil and EAS should see the world
the same way.

But IMHO only for the

find_energy_efficient_cpu()
  compute_energy()
    eenv_pd_max_util()
      util = cpu_util_next(..., p, ...)
      effective_cpu_util(..., util, FREQUENCY_UTIL, ...)
                                    ^^^^^^^^^^^^^^
case.

Not sure what I do for the task contribution? We use
task_util(p)/_task_util_est(p) inside cpu_util_next().
Do I have to consider p->se.avg.runnable_avg as well?

I don't think that we have a testcase showing any diff for this change
individually though.

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