linux-kernel - Re: [PATCH v6 1/4] sched/fair: Fix attaching task sched avgs twice when switching to fair or changing task group

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Message-ID: <20160617113101.GO30154@twins.programming.kicks-ass.net>
Date:	Fri, 17 Jun 2016 13:31:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Yuyang Du <yuyang.du@...el.com>, Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH v6 1/4] sched/fair: Fix attaching task sched avgs twice
 when switching to fair or changing task group

On Thu, Jun 16, 2016 at 11:21:55PM +0200, Vincent Guittot wrote:
> Your proposal below looks good to me

> > ---
> >  kernel/sched/fair.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index f75930bdd326..5d8fa135bbc5 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -8349,6 +8349,7 @@ static void detach_task_cfs_rq(struct task_struct *p)
> >  {
> >         struct sched_entity *se = &p->se;
> >         struct cfs_rq *cfs_rq = cfs_rq_of(se);
> > +       u64 now = cfs_rq_clock_task(cfs_rq);
> >
> >         if (!vruntime_normalized(p)) {
> >                 /*
> > @@ -8360,6 +8361,7 @@ static void detach_task_cfs_rq(struct task_struct *p)
> >         }
> >
> >         /* Catch up with the cfs_rq and remove our load when we leave */
> > +       update_cfs_rq_load_avg(now, cfs_rq, false);
> >         detach_entity_load_avg(cfs_rq, se);
> >  }
> >
> > @@ -8367,6 +8369,7 @@ static void attach_task_cfs_rq(struct task_struct *p)
> >  {
> >         struct sched_entity *se = &p->se;
> >         struct cfs_rq *cfs_rq = cfs_rq_of(se);
> > +       u64 now = cfs_rq_clock_task(cfs_rq);
> >
> >  #ifdef CONFIG_FAIR_GROUP_SCHED
> >         /*
> > @@ -8377,6 +8380,7 @@ static void attach_task_cfs_rq(struct task_struct *p)
> >  #endif
> >
> >         /* Synchronize task with its cfs_rq */
> > +       update_cfs_rq_load_avg(now, cfs_rq, false);
> >         attach_entity_load_avg(cfs_rq, se);
> >
> >         if (!vruntime_normalized(p))

Should we also call update_tg_load_avg() if update_cfs_rq_load_avg()
returns? Most sites seem to do this.

Someone should document these things somewhere....