linux-kernel - Re: 4.3 group scheduling regression

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Message-ID: <20151012204225.GN11102@intel.com>
Date:	Tue, 13 Oct 2015 04:42:25 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: 4.3 group scheduling regression

On Tue, Oct 13, 2015 at 06:08:34AM +0200, Mike Galbraith wrote:
> It sounded like you wanted me to run the below alone.  If so, it's a nogo.
  
Yes, thanks.

Then it is the sad fact that after migrate and removed_load_avg is added
in migrate_task_rq_fair(), we don't get a chance to update the tg so fast
that at the destination the mplayer is weighted to the group's share.

>  -----------------------------------------------------------------------------------------------------------------
>   Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at       |
>  -----------------------------------------------------------------------------------------------------------------
>   oink:(8)              | 787001.236 ms |    21641 | avg:    0.377 ms | max:   21.991 ms | max at:     51.504005 s
>   mplayer:(25)          |   4256.224 ms |     7264 | avg:   19.698 ms | max: 2087.489 ms | max at:    115.294922 s
>   Xorg:1011             |   1507.958 ms |     4081 | avg:    8.349 ms | max: 1652.200 ms | max at:    126.908021 s
>   konsole:1752          |    697.806 ms |     1186 | avg:    5.749 ms | max:  160.189 ms | max at:     53.037952 s
>   testo:(9)             |    438.164 ms |     2551 | avg:    6.616 ms | max:  215.527 ms | max at:    117.302455 s
>   plasma-desktop:1716   |    280.418 ms |     1624 | avg:    3.701 ms | max:  574.806 ms | max at:     53.582261 s
>   kwin:1708             |    144.986 ms |     2422 | avg:    3.301 ms | max:  315.707 ms | max at:    116.555721 s
> 
> > --
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 4df37a4..3dba883 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -2686,12 +2686,13 @@ static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);
> >  static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> >  {
> >  	struct sched_avg *sa = &cfs_rq->avg;
> > -	int decayed;
> > +	int decayed, updated = 0;
> >  
> >  	if (atomic_long_read(&cfs_rq->removed_load_avg)) {
> >  		long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
> >  		sa->load_avg = max_t(long, sa->load_avg - r, 0);
> >  		sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
> > +		updated = 1;
> >  	}
> >  
> >  	if (atomic_long_read(&cfs_rq->removed_util_avg)) {
> > @@ -2708,7 +2709,7 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> >  	cfs_rq->load_last_update_time_copy = sa->last_update_time;
> >  #endif
> >  
> > -	return decayed;
> > +	return decayed | updated;

A typo: decayed || updated, but shouldn't make any difference.

> >  }
> >  
> >  /* Update task and its cfs_rq load average */
> 
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