linux-kernel - Re: [PATCH 1/8] sched: introduce task_se_h

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Message-ID: <9e75dd03-23e5-8ab3-8f5c-789b2581b3a7@arm.com>
Date:   Wed, 19 Jun 2019 17:18:15 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Rik van Riel <riel@...riel.com>, peterz@...radead.org
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org, kernel-team@...com,
        morten.rasmussen@....com, tglx@...utronix.de,
        dietmar.eggeman@....com, mgorman@...hsingularity.com,
        vincent.guittot@...aro.org
Subject: Re: [PATCH 1/8] sched: introduce task_se_h_load helper

On 6/19/19 3:57 PM, Rik van Riel wrote:
> On Wed, 2019-06-19 at 14:52 +0200, Dietmar Eggemann wrote:
> 
>>> @@ -7833,14 +7834,19 @@ static void update_cfs_rq_h_load(struct
>>> cfs_rq *cfs_rq)
>>>  	}
>>>  }
>>>  
>>> -static unsigned long task_h_load(struct task_struct *p)
>>> +static unsigned long task_se_h_load(struct sched_entity *se)
>>>  {
>>> -	struct cfs_rq *cfs_rq = task_cfs_rq(p);
>>> +	struct cfs_rq *cfs_rq = cfs_rq_of(se);
>>>  
>>>  	update_cfs_rq_h_load(cfs_rq);
>>> -	return div64_ul(p->se.avg.load_avg * cfs_rq->h_load,
>>> +	return div64_ul(se->avg.load_avg * cfs_rq->h_load,
>>>  			cfs_rq_load_avg(cfs_rq) + 1);
>>>  }
>>
>> I wonder if this is necessary. I placed a BUG_ON(!entity_is_task(se))
>> into task_se_h_load() after I applied the whole patch-set and ran
>> some
>> taskgroup related testcases. It didn't hit.
>>
>> So why not use task_h_load(task_of(se)) instead?
>>
>> [...]
> 
> That would work, but task_h_load then dereferences
> task->se to get the se->avg.load_avg value.
> 
> Going back to task from the se, only to then get the
> se from the task seems a little unnecessary :)
> 
> Can you explain why you think task_h_load(task_of(se))
> would be better? I think I may be overlooking something.

Ah, OK, I just wanted to avoid having task_se_h_load() and task_h_load()
at the same time. You could replace the remaining calls to
task_h_load(p) with task_se_h_load(&p->se) in this case.

- task_load = task_h_load(p);
+ task_load = task_se_h_load(&p->se);

Not that important though right now ...