Re: [PATCH] sched/deadline: do not try to push tasks if pinned task switches to dl

[Wanpeng Li]

ä 10/10/14, 6:56 PM, Peter Zijlstra åé:
> On Fri, Oct 10, 2014 at 06:26:42PM +0800, Wanpeng Li wrote:
> > ä 10/10/14, 6:10 PM, Peter Zijlstra åé:
> > > On Fri, Oct 10, 2014 at 10:43:17AM +0800, Wanpeng Li wrote:
> > > > 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 had had
> > > > several dl tasks before they have already been considered as candidates
> > > > to be pushed (or pulled). This patch does the same behavior as rt class
> > > > which introduced by commit 104479 (sched/rt: Do not try to push tasks
> > > > if pinned task switches to RT).
> > > Checkpatch rightly complains:
> > >
> > > ERROR: Please use 12 or more chars for the git commit ID like: 'commit 10447917551e ("sched/rt: Do not try to push tasks if pinned task switches to RT")'
> > > #12:
> > > which introduced by commit 104479 (sched/rt: Do not try to push tasks
> > I also got this warning before send out the patch, however, I check 6 chars
> > is enough for this commit. Anyway, I will send a newer version later.
> It is currently, it might not be in the future. I've already had hash
> collisions with 8 char hashes. And the fact thats it in the changelog
> means it can (and therefore) will be referenced at some point in the
> future. If by that point there is a collision...

Got it, thanks for your pointing out.

Regards,
Wanpeng Li

From 247460238414744119265d6aa92f4bf006b060aa Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
Date: Fri, 10 Oct 2014 10:09:37 +0800
Subject: [PATCH v2] 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 had had
several dl tasks before they have already been considered as candidates
to be pushed (or pulled). This patch done 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 <wanpeng.li@xxxxxxxxxxxxxxx>
---
v1 -> v2:
 * use 12 or more chars for the git commit ID

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

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index abfaf3d..cf7c9b6 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1603,7 +1603,8 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 
 	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 */
-- 
1.9.1