linux-kernel - Re: [PATCH] sched/rt: fix rt timer activation/deactivation

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Date:	Wed, 26 Feb 2014 03:37:38 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	tkhai@...dex.ru
Cc:	Juri Lelli <juri.lelli@...il.com>, mingo@...hat.com,
	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/rt: fix rt timer activation/deactivation

On Wed, 2014-02-26 at 00:56 +0400, Kirill Tkhai wrote: 
> On Вт, 2014-02-25 at 17:05 +0100, Juri Lelli wrote:
> > Destroy rt bandwidth timer when rq has no more RT tasks, even when
> > CONFIG_RT_GROUP_SCHED is not set.
> > 
> > Signed-off-by: Juri Lelli <juri.lelli@...il.com>
> > ---
> >  kernel/sched/rt.c |   10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> > index a2740b7..7dba25a 100644
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -86,12 +86,12 @@ void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)
> >  	raw_spin_lock_init(&rt_rq->rt_runtime_lock);
> >  }
> >  
> > -#ifdef CONFIG_RT_GROUP_SCHED
> >  static void destroy_rt_bandwidth(struct rt_bandwidth *rt_b)
> >  {
> >  	hrtimer_cancel(&rt_b->rt_period_timer);
> >  }
> >  
> > +#ifdef CONFIG_RT_GROUP_SCHED
> >  #define rt_entity_is_task(rt_se) (!(rt_se)->my_q)
> >  
> >  static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
> > @@ -1011,8 +1011,12 @@ inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
> >  	start_rt_bandwidth(&def_rt_bandwidth);
> >  }
> >  
> > -static inline
> > -void dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}
> > +static void
> > +dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
> > +{
> > +	if (!rt_rq->rt_nr_running)
> > +		destroy_rt_bandwidth(&def_rt_bandwidth);
> > +}
> 
> The problem is bandwidth timer is not per-cpu. It's only for all
> processors from the span (sched_rt_period_mask()). Other CPUs may
> have enqueued RT tasks. So, it's not possible to do this.

BTW, I noticed you can no longer turn the turn the noisy thing off since
we grew DL.  I added an old SGI boot parameter to tell it to go away.

-Mike

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