[PATCH]sched/rt.c: leaf_rt_rq_list contains empty queues. Fix it

[PATCH]sched/rt.c: leaf_rt_rq_list contains empty queues. Fix it

[Kirill Tkhai]

Function __enqueue_rt_entity() adds an empty queue to leaf_rt_rq_list.

So, pick_next_highest_task_rt() picks empty queues. Fix it.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
---
 kernel/sched/rt.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 944cb68..b07edb9 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1103,7 +1103,7 @@ static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
 	if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
 		return;
 
-	if (!rt_rq->rt_nr_running)
+	if (rt_rq->rt_nr_running)
 		list_add_leaf_rt_rq(rt_rq);
 
 	if (head)

Re: [PATCH]sched/rt.c: leaf_rt_rq_list contains empty queues. Fix it

[Kirill Tkhai]

Second version. Add every not empty queue once. The patch:

Function __enqueue_rt_entity() adds an empty queue to leaf_rt_rq_list.

So, pick_next_highest_task_rt() picks empty queues. Fix it.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
---
 kernel/sched/rt.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 944cb68..97a0954 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1103,7 +1103,7 @@ static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
 	if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
 		return;
 
-	if (!rt_rq->rt_nr_running)
+	if (rt_rq->rt_nr_running == 1)
 		list_add_leaf_rt_rq(rt_rq);
 
 	if (head)

Re: [PATCH]sched/rt.c: leaf_rt_rq_list contains empty queues. Fix it

[Steven Rostedt]

On Fri, 2012-09-21 at 18:21 +0400, Kirill Tkhai wrote:
> Second version. Add every not empty queue once. The patch:
> 
> Function __enqueue_rt_entity() adds an empty queue to leaf_rt_rq_list.
> 
> So, pick_next_highest_task_rt() picks empty queues. Fix it.
> 
> Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
> ---
>  kernel/sched/rt.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 944cb68..97a0954 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1103,7 +1103,7 @@ static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
>  	if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
>  		return;
>  
> -	if (!rt_rq->rt_nr_running)
> +	if (rt_rq->rt_nr_running == 1)
>  		list_add_leaf_rt_rq(rt_rq);

Again, the rt_nr_running hasn't been incremented yet. This patch will
add it when the rq gets a second task.

-- Steve

>  
>  	if (head)

Re: [PATCH]sched/rt.c: leaf_rt_rq_list contains empty queues. Fix it

[Kirill Tkhai]

> Again, the rt_nr_running hasn't been incremented yet. This patch will
> add it when the rq gets a second task.
>
> -- Steve

Right, thanks for the explanation

Kirill

Re: [PATCH]sched/rt.c: leaf_rt_rq_list contains empty queues. Fix it

[Steven Rostedt]

On Fri, 2012-09-21 at 17:35 +0400, Kirill Tkhai wrote:
> Function __enqueue_rt_entity() adds an empty queue to leaf_rt_rq_list.
> 
> So, pick_next_highest_task_rt() picks empty queues. Fix it.

Do you have an example where this breaks?

> 
> Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
> ---
>  kernel/sched/rt.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 944cb68..b07edb9 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1103,7 +1103,7 @@ static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
>  	if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
>  		return;
>  
> -	if (!rt_rq->rt_nr_running)
> +	if (rt_rq->rt_nr_running)
>  		list_add_leaf_rt_rq(rt_rq);

Note, the list_add_leaf_rt_rq() is called when the first task is queued
up. The function here is __enqueue_rt_entity(), which will increment
rt_rq->rt_nr_running. If this is the first entry we add the queue now,
as the __dequeue_rt_entity() does the list_del_leaf_rt_rq() when it goes
to zero.

-- Steve

>  
>  	if (head)