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

[Kirill Tkhai <tkhai@yandex.ru>]

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@gmail.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.

>  
>  #endif /* CONFIG_RT_GROUP_SCHED */
>