[PATCH] sched/rt.c: use list_is_singular() instead of '->prev != ->next'

[PATCH] sched/rt.c: use list_is_singular() instead of '->prev != ->next'

[Hui Su]

Use the list_is_singular(&rt_se->run_list) api instead of
'rt_se->run_list.prev != rt_se->run_list.next'.
Fix a comment by the way, and make the comment more clearly.

Signed-off-by: Hui Su <sh_def@163.com>
---
 kernel/sched/rt.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 49ec096a8aa1..1479d00656b4 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2381,7 +2381,7 @@ static inline void watchdog(struct rq *rq, struct task_struct *p) { }
  *
  * NOTE: This function can be called remotely by the tick offload that
  * goes along full dynticks. Therefore no local assumption can be made
- * and everything must be accessed through the @rq and @curr passed in
+ * and everything must be accessed through the @rq and @p passed in
  * parameters.
  */
 static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
@@ -2406,11 +2406,11 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
 	p->rt.time_slice = sched_rr_timeslice;
 
 	/*
-	 * Requeue to the end of queue if we (and all of our ancestors) are not
-	 * the only element on the queue
+	 * Requeue to the end of rt_prio_array queue if we (and all of our
+	 * ancestors) are not the only element on the rt_prio_array queue.
 	 */
 	for_each_sched_rt_entity(rt_se) {
-		if (rt_se->run_list.prev != rt_se->run_list.next) {
+		if (!list_is_singular(&rt_se->run_list)) {
 			requeue_task_rt(rq, p, 0);
 			resched_curr(rq);
 			return;
-- 
2.25.1

Re: [PATCH] sched/rt.c: use list_is_singular() instead of '->prev != ->next'

[Steven Rostedt]

On Tue, 27 Oct 2020 01:41:52 +0800
Hui Su <sh_def@163.com> wrote:

> Use the list_is_singular(&rt_se->run_list) api instead of
> 'rt_se->run_list.prev != rt_se->run_list.next'.
> Fix a comment by the way, and make the comment more clearly.
> 
> Signed-off-by: Hui Su <sh_def@163.com>
> ---
>  kernel/sched/rt.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 49ec096a8aa1..1479d00656b4 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2381,7 +2381,7 @@ static inline void watchdog(struct rq *rq, struct task_struct *p) { }
>   *
>   * NOTE: This function can be called remotely by the tick offload that
>   * goes along full dynticks. Therefore no local assumption can be made
> - * and everything must be accessed through the @rq and @curr passed in
> + * and everything must be accessed through the @rq and @p passed in
>   * parameters.
>   */
>  static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
> @@ -2406,11 +2406,11 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
>  	p->rt.time_slice = sched_rr_timeslice;
>  
>  	/*
> -	 * Requeue to the end of queue if we (and all of our ancestors) are not
> -	 * the only element on the queue
> +	 * Requeue to the end of rt_prio_array queue if we (and all of our
> +	 * ancestors) are not the only element on the rt_prio_array queue.
>  	 */
>  	for_each_sched_rt_entity(rt_se) {
> -		if (rt_se->run_list.prev != rt_se->run_list.next) {
> +		if (!list_is_singular(&rt_se->run_list)) {

Perhaps there should be a list_has_more_than_one() API, as list_is_singular
requires two checks, and the "more_than_one" only requires a single check.

list_is_singular() is:

		return !list_empty(list) && (list->next == list->prev);


which is more work than what you are replacing.

-- Steve


>  			requeue_task_rt(rq, p, 0);
>  			resched_curr(rq);
>  			return;

Re:Re: [PATCH] sched/rt.c: use list_is_singular() instead of '->prev != ->next'

[苏辉]

>Perhaps there should be a list_has_more_than_one() API, as list_is_singular
>requires two checks, and the "more_than_one" only requires a single check.
>
>list_is_singular() is:
>
>		return !list_empty(list) && (list->next == list->prev);
>
>
>which is more work than what you are replacing.
>

Hi, Steve:

Thanks for your explanation.
Maybe we should add another api called "list_more_than_one" just without
list_empty() check.

I will send PATCH V2 later.

Thank.