linux-kernel - Re: [PATCH] sched/rt.c remove unnecessary parameter in pick_next_rt

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Date:   Tue, 29 Sep 2020 20:29:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Hui Su <sh_def@....com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/rt.c remove unnecessary parameter in
 pick_next_rt_entity

On Wed, 30 Sep 2020 00:56:40 +0800
Hui Su <sh_def@....com> wrote:

> struct rq is not necessary for pick_next_rt_entity(),
> we can get next sched_rt_entity just from struct rt_rq.
> 
> Signed-off-by: Hui Su <sh_def@....com>
> ---
>  kernel/sched/rt.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index f215eea6a966..113965e1952c 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1593,11 +1593,9 @@ static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool f
>  	rt_queue_push_tasks(rq);
>  }
>  
> -static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
> -						   struct rt_rq *rt_rq)
> +static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
>  {
>  	struct rt_prio_array *array = &rt_rq->active;
> -	struct sched_rt_entity *next = NULL;
>  	struct list_head *queue;
>  	int idx;
>  
> @@ -1605,9 +1603,8 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
>  	BUG_ON(idx >= MAX_RT_PRIO);
>  
>  	queue = array->queue + idx;
> -	next = list_entry(queue->next, struct sched_rt_entity, run_list);
>  
> -	return next;
> +	return list_entry(queue->next, struct sched_rt_entity, run_list);

The above code looks to be left over from a time that there was a goto
out; with out: being between the next = list_etry() and the return
next. This was removed back in 2008 with commit 326587b84078 ("sched:
fix goto retry in pick_next_task_rt()").

The above looks fine to me.

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve


>  }
>  
>  static struct task_struct *_pick_next_task_rt(struct rq *rq)
> @@ -1616,7 +1613,7 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)
>  	struct rt_rq *rt_rq  = &rq->rt;
>  
>  	do {
> -		rt_se = pick_next_rt_entity(rq, rt_rq);
> +		rt_se = pick_next_rt_entity(rt_rq);
>  		BUG_ON(!rt_se);
>  		rt_rq = group_rt_rq(rt_se);
>  	} while (rt_rq);