linux-kernel - Re: [PATCH 05/10] sched,fair: remove cfs rqs from leaf_cfs_rq

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Date:   Thu, 04 Jul 2019 21:02:32 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>, Paul Turner <pjt@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH 05/10] sched,fair: remove cfs rqs from leaf_cfs_rq_list
 bottom up

On Thu, 2019-07-04 at 11:33 +0200, Vincent Guittot wrote:
> On Fri, 28 Jun 2019 at 22:49, Rik van Riel <riel@...riel.com> wrote:
> > Reducing the overhead of the CPU controller is achieved by not
> > walking
> > all the sched_entities every time a task is enqueued or dequeued.

> > @@ -7687,6 +7700,10 @@ static inline bool cfs_rq_is_decayed(struct
> > cfs_rq *cfs_rq)
> >         if (cfs_rq->avg.util_sum)
> >                 return false;
> > 
> > +       /* Remove decayed parents once their decayed children are
> > gone. */
> > +       if (cfs_rq->children_on_list)
> 
> I'm not sure that you really need to count whether childrens are on
> the list.
> Instead you can take advantage of the list ordering and you only have
> to test if the previous cfs_rq in the list is a child. If it's not
> then there is no more child
> 
> and you can remove the new field children_on_list and inc/dec it

Good suggestion. I'll do that for v3.

Thank you.

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