sched/deadline: do not try to push tasks if pinned task switches to dl

As Kirill mentioned(https://lkml.org/lkml/2013/1/29/118):
| If rq has already had 2 or more pushable tasks and we try to add a | pinned task then call of push_rt_task will just waste a time.

Just switched pinned task is not able to be pushed. If the rq has had several dl tasks before they have already been considered as candidates to be pushed (or pulled). This patch implements the same behavior as rt class which introduced by commit 10447917551e ("sched/rt: Do not try to push tasks if pinned task switches to RT").

Signed-off-by Wanpeng Li <[email protected]>

---
v2 -> v3:
* cleanup patch description
* align && to p->nr_cpus_allowed
v1 -> v2:
* use 12 or more chars for the git commit ID

 kernel/sched/deadline.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

kernel/sched/deadline.c +0 -0

index abfaf3d..bd5e479 100644

Quoted 27 lines · Wanpeng Li

As Kirill mentioned(https://lkml.org/lkml/2013/1/29/118):
| If rq has already had 2 or more pushable tasks and we try to add a | pinned task then call of push_rt_task will just waste a time.

Just switched pinned task is not able to be pushed. If the rq has had several dl tasks before they have already been considered as candidates to be pushed (or pulled). This patch implements the same behavior as rt class which introduced by commit 10447917551e ("sched/rt: Do not try to push tasks if pinned task switches to RT").

Signed-off-by Wanpeng Li <[email protected]>

---
v2 -> v3:
* cleanup patch description
* align && to p->nr_cpus_allowed
v1 -> v2:
* use 12 or more chars for the git commit ID

 kernel/sched/deadline.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

kernel/sched/deadline.c +0 -0

index abfaf3d..bd5e479 100644
@@ -1603,7 +1603,8 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 

kernel/sched/deadline.c static void switched_to_dl(struct rq *rq, struct task_struct *p) · line 1610

Quoted 9 lines

kernel/sched/deadline.c +2 -1

 	if (task_on_rq_queued(p) && rq->curr != p) {
 #ifdef CONFIG_SMP
-		if (rq->dl.overloaded && push_dl_task(rq) && rq != task_rq(p))
+		if (p->nr_cpus_allowed > 1 && rq->dl.overloaded &&
+			push_dl_task(rq) && rq != task_rq(p))
 			/* Only reschedule if pushing failed */
 			check_resched = 0;
 #endif /* CONFIG_SMP */

I'm looking at some old changes for sched-deadline, and I stumbled across this. As I'm working on sched deadline tests, I've discovered that they can't have cpu affinity. They are limited to their sched domains. That is, sched deadline tasks have whatever affinity that the domain they happen to be in has.

Is there a condition where rq != task_rq(p) and p->nr_cpus_allowed > 1 isn't true?

Quoted 4 lines

I'm looking at some old changes for sched-deadline, and I stumbled across this. As I'm working on sched deadline tests, I've discovered that they can't have cpu affinity. They are limited to their sched domains. That is, sched deadline tasks have whatever affinity that the

Quoted 4 lines

domain they happen to be in has.

Is there a condition where rq != task_rq(p) and p->nr_cpus_allowed > 1 isn't true?

When holding rq->lock, no. I suppose the patch was just to mirror rt and someone 'forgot' about the extra constraints on dl tasks.