linux-kernel - Re: [Patch v5 4/6] sched/fair: update cpu

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Date:   Wed, 6 Nov 2019 12:31:29 -0500
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     mingo@...hat.com, peterz@...radead.org, ionela.voinescu@....com,
        vincent.guittot@...aro.org, rui.zhang@...el.com,
        edubezval@...il.com, qperret@...gle.com,
        linux-kernel@...r.kernel.org, amit.kachhap@...il.com,
        javi.merino@...nel.org, daniel.lezcano@...aro.org
Subject: Re: [Patch v5 4/6] sched/fair: update cpu_capcity to reflect thermal
 pressure

On 11/06/2019 11:56 AM, Qais Yousef wrote:
> On 11/05/19 13:49, Thara Gopinath wrote:
>> cpu_capacity relflects the maximum available capacity of a cpu. Thermal
>> pressure on a cpu means this maximum available capacity is reduced. This
>> patch reduces the average thermal pressure for a cpu from its maximum
>> available capacity so that cpu_capacity reflects the actual
>> available capacity.
>>
>> Other signals that are deducted from cpu_capacity to reflect the actual
>> capacity available are rt and dl util_avg. util_avg tracks a binary signal
>> and uses the weights 1024 and 0. Whereas thermal pressure is tracked
>> using load_avg. load_avg uses the actual "delta" capacity as the weight.
> 
> I think you intended to put this as comment...
> 
>>
>> Signed-off-by: Thara Gopinath <thara.gopinath@...aro.org>
>> ---
>>  kernel/sched/fair.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 9fb0494..5f6c371 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -7738,6 +7738,7 @@ static unsigned long scale_rt_capacity(struct sched_domain *sd, int cpu)
>>  
>>  	used = READ_ONCE(rq->avg_rt.util_avg);
>>  	used += READ_ONCE(rq->avg_dl.util_avg);
>> +	used += READ_ONCE(rq->avg_thermal.load_avg);
> 
> ... here?

I did not!  But I can.
> 
> I find the explanation hard to parse too. Do you think you can rephrase it?
> Something based on what you wrote here would be more understandable IMHO:
> https://lore.kernel.org/lkml/5DBB05BC.40502@linaro.org/
I will try to rephrase it! I am sorry that you found it hard to parse.
Honestly, I cannot copy paste the code snippet I pointed out to you here
in comment.(And I think that is the reason you found it easier to
understand) But I will try my best to put it in words.

> 
> 
> Thanks!
> 
> --
> Qais Yousef
> 
>>  
>>  	if (unlikely(used >= max))
>>  		return 1;
>> -- 
>> 2.1.4
>>


-- 
Warm Regards
Thara