linux-kernel - Re: [PATCH 09/15] sched,fair: refactor enqueue/dequeue

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Message-ID: <6d07046810f4a490960d0124e99fe9cf546e9d10.camel@surriel.com>
Date:   Tue, 03 Sep 2019 16:27:54 -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 09/15] sched,fair: refactor enqueue/dequeue_entity

On Tue, 2019-09-03 at 17:38 +0200, Vincent Guittot wrote:
> Hi Rik,
> 
> On Thu, 22 Aug 2019 at 04:18, Rik van Riel <riel@...riel.com> wrote:
> > Refactor enqueue_entity, dequeue_entity, and update_load_avg, in
> > order
> > to split out the things we still want to happen at every level in
> > the
> > cgroup hierarchy with a flat runqueue from the things we only need
> > to
> > happen once.
> > 
> > No functional changes.
> > 
> > Signed-off-by: Rik van Riel <riel@...riel.com>
> > ---
> >  kernel/sched/fair.c | 64 +++++++++++++++++++++++++++++----------
> > ------
> >  1 file changed, 42 insertions(+), 22 deletions(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 74ee22c59d13..7b0d95f2e3a8 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3502,7 +3502,7 @@ static void detach_entity_load_avg(struct
> > cfs_rq *cfs_rq, struct sched_entity *s
> >  #define DO_ATTACH      0x4
> > 
> >  /* Update task and its cfs_rq load average */
> > -static inline void update_load_avg(struct cfs_rq *cfs_rq, struct
> > sched_entity *se, int flags)
> > +static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct
> > sched_entity *se, int flags)
> >  {
> >         u64 now = cfs_rq_clock_pelt(cfs_rq);
> >         int decayed;
> > @@ -3531,6 +3531,8 @@ static inline void update_load_avg(struct
> > cfs_rq *cfs_rq, struct sched_entity *s
> > 
> >         } else if (decayed && (flags & UPDATE_TG))
> >                 update_tg_load_avg(cfs_rq, 0);
> > +
> > +       return decayed;
> 
> This is a functional change, isn't it ?
> update_cfs_group is now called only if decayed but we can we attach a
> task during the enqueue and there is no decay

Yes, it is, and patch 11 changes the way this functional
change is done.

If you want, I can change this patch to not have the
functional change, though in the end it should not make
any difference.

-- 
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