linux-kernel - Re: [PATCH 09/10] sched,fair: add helper functions for flattened runqueue

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Date:   Mon, 01 Jul 2019 16:53:37 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        dietmar.eggemann@....com, peterz@...radead.org, mingo@...hat.com,
        morten.rasmussen@....com, tglx@...utronix.de,
        mgorman@...hsingularity.net, vincent.guittot@...aro.org
Subject: Re: [PATCH 09/10] sched,fair: add helper functions for flattened
 runqueue

On Mon, 2019-07-01 at 16:20 -0400, Josef Bacik wrote:
> 
> 
> > +static unsigned long task_se_h_weight(struct sched_entity *se)
> > +{
> > +	struct cfs_rq *cfs_rq;
> > +
> > +	if (!task_se_in_cgroup(se))
> > +		return se->load.weight;
> > +
> > +	cfs_rq = group_cfs_rq_of_parent(se);
> > +	update_cfs_rq_h_load(cfs_rq);
> > +
> > +	/* Reduce the load.weight by the h_load of the group the task
> > is in. */
> > +	return (cfs_rq->h_load * se->load.weight) >>
> > SCHED_FIXEDPOINT_SHIFT;
> 
> This should be
> 
> scale_load_down(cfs_rq->h_load * se->load.weight);

That may be the same mathematically, but it is
different conceptually.

If we convert CFS to have full load resolution with
cgroups (which we probably want), then scale_load_down
becomes a noop, while this shift continues doing the
right thing.

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