linux-kernel - Re: [PATCH] sched/core: use correct cpu_capacity in wake_affine

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Date:   Wed, 16 Nov 2022 19:17:18 +0800
From:   Honglei Wang <wanghonglei@...ichuxing.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Honglei Wang <wanghonglei@...iglobal.com>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/core: use correct cpu_capacity in
 wake_affine_weight()



On 2022/11/16 19:00, Vincent Guittot wrote:
> On Wed, 16 Nov 2022 at 10:12, Honglei Wang <wanghonglei@...iglobal.com> wrote:
>>
>> It seems make more sense to do the load weight calculation with
>> respective cpu_capacity.
>>
>> Signed-off-by: Honglei Wang <wanghonglei@...iglobal.com>
>> ---
>>   kernel/sched/fair.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index e4a0b8bd941c..a9f75040969b 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6262,13 +6262,13 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
>>          this_eff_load += task_load;
>>          if (sched_feat(WA_BIAS))
>>                  this_eff_load *= 100;
>> -       this_eff_load *= capacity_of(prev_cpu);
>> +       this_eff_load *= capacity_of(this_cpu);
>>
>>          prev_eff_load = cpu_load(cpu_rq(prev_cpu));
>>          prev_eff_load -= task_load;
>>          if (sched_feat(WA_BIAS))
>>                  prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;
>> -       prev_eff_load *= capacity_of(this_cpu);
>> +       prev_eff_load *= capacity_of(prev_cpu);
> 
> we want to test :
>      (cpu_load(this_rq) + task_h_load(p) ) / capacity_of(this_cpu)  <
> cpu_load(prev_rq) / capacity_of(prev_cpu)
> 
> but instead of doing expensive division, we do the below which gives
> the same result
>      (cpu_load(this_rq) + task_h_load(p) ) * capacity_of(prev_cpu)  <
> cpu_load(prev_rq) * capacity_of(this_cpu)
> 
> 

ha, I misunderstand the strategy, thanks for coaching, Vincent.

>>
>>          /*
>>           * If sync, adjust the weight of prev_eff_load such that if
>> --
>> 2.14.1
>>