linux-kernel - Re: [PATCH] sched/rt: fix rt runtime corrupt when dl refuse a smaller bandwidth

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Message-ID: <546B8934.5040100@arm.com>
Date:	Tue, 18 Nov 2014 18:00:20 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Kirill Tkhai <ktkhai@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: fix rt runtime corrupt when dl refuse a smaller
 bandwidth

Hi,

On 13/11/14 08:47, Wanpeng Li wrote:
> Dl class will refuse the bandwidth being set to some value smaller 
> than the currently allocated bandwidth in any of the root_domains 
> through sched_rt_runtime_us and sched_rt_period_us. RT runtime will 
> be set according to sched_rt_runtime_us before dl class verify if 
> the new bandwidth is suitable in the case of !CONFIG_RT_GROUP_SCHED.
> 
> However, rt runtime will be corrupt if dl refuse the new bandwidth 
> since there is no undo to reset the rt runtime to the old value. 
> 

Can't we just move sched_dl_global_constraints() before
sched_rt_global_constraints(), and change the name of the
former to sched_dl_global_validate() ?

Thanks,

- Juri

> This patch fix it by setting rt runtime after all kinds of rational 
> checking in the case of !CONFIG_RT_GROUP_SCHED.
> 
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>  kernel/sched/core.c | 30 ++++++++++++++++--------------
>  1 file changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 2e7578a..355dde3 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7795,20 +7795,7 @@ static int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)
>  #else /* !CONFIG_RT_GROUP_SCHED */
>  static int sched_rt_global_constraints(void)
>  {
> -	unsigned long flags;
> -	int i, ret = 0;
> -
> -	raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
> -	for_each_possible_cpu(i) {
> -		struct rt_rq *rt_rq = &cpu_rq(i)->rt;
> -
> -		raw_spin_lock(&rt_rq->rt_runtime_lock);
> -		rt_rq->rt_runtime = global_rt_runtime();
> -		raw_spin_unlock(&rt_rq->rt_runtime_lock);
> -	}
> -	raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
> -
> -	return ret;
> +	return 0;
>  }
>  #endif /* CONFIG_RT_GROUP_SCHED */
>  
> @@ -7890,6 +7877,21 @@ static int sched_rt_global_validate(void)
>  
>  static void sched_rt_do_global(void)
>  {
> +#ifndef CONFIG_RT_GROUP_SCHED
> +	unsigned long flags;
> +	int i;
> +
> +	raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
> +	for_each_possible_cpu(i) {
> +		struct rt_rq *rt_rq = &cpu_rq(i)->rt;
> +
> +		raw_spin_lock(&rt_rq->rt_runtime_lock);
> +		rt_rq->rt_runtime = global_rt_runtime();
> +		raw_spin_unlock(&rt_rq->rt_runtime_lock);
> +	}
> +	raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
> +#endif
> +
>  	def_rt_bandwidth.rt_runtime = global_rt_runtime();
>  	def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
>  }
> 

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