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

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Date:   Wed, 19 Jun 2019 09:57:14 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Dietmar Eggemann <dietmar.eggemann@....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 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.

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