[RESEND PATCH v3] sched/deadline: Remove unnecessary condition in push_dl_task()

[RESEND PATCH v3] sched/deadline: Remove unnecessary condition in push_dl_task()

[Byungchul Park]

pick_next_pushable_dl_task(rq) has BUG_ON(rq->cpu != task_cpu(task))
when it returns a task other than NULL, which means that task_cpu(task)
must be rq->cpu. So if task == next_task, then task_cpu(next_task) must
be rq->cpu as well. Remove the redundant condition and make code simpler.

By this patch, unnecessary one branch and two LOAD operations in 'if'
statement can be avoided.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Juri Lelli <juri.lelli@arm.com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
---
 kernel/sched/deadline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 27737f3..ad8d577 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1483,7 +1483,7 @@ static int push_dl_task(struct rq *rq)
 		 * then possible that next_task has migrated.
 		 */
 		task = pick_next_pushable_dl_task(rq);
-		if (task_cpu(next_task) == rq->cpu && task == next_task) {
+		if (task == next_task) {
 			/*
 			 * The task is still there. We don't try
 			 * again, some other cpu will pull it when ready.
-- 
1.9.1

Re: [RESEND PATCH v3] sched/deadline: Remove unnecessary condition in push_dl_task()

[Byungchul Park]

On Fri, May 12, 2017 at 10:05:59AM +0900, Byungchul Park wrote:
> pick_next_pushable_dl_task(rq) has BUG_ON(rq->cpu != task_cpu(task))
> when it returns a task other than NULL, which means that task_cpu(task)
> must be rq->cpu. So if task == next_task, then task_cpu(next_task) must
> be rq->cpu as well. Remove the redundant condition and make code simpler.
> 
> By this patch, unnecessary one branch and two LOAD operations in 'if'
> statement can be avoided.

+cc rostedt@goodmis.org
+cc juri.lelli@arm.com
+cc bristot@redhat.com

> 
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> Reviewed-by: Juri Lelli <juri.lelli@arm.com>
> Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
> ---
>  kernel/sched/deadline.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 27737f3..ad8d577 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1483,7 +1483,7 @@ static int push_dl_task(struct rq *rq)
>  		 * then possible that next_task has migrated.
>  		 */
>  		task = pick_next_pushable_dl_task(rq);
> -		if (task_cpu(next_task) == rq->cpu && task == next_task) {
> +		if (task == next_task) {
>  			/*
>  			 * The task is still there. We don't try
>  			 * again, some other cpu will pull it when ready.
> -- 
> 1.9.1

Re: [RESEND PATCH v3] sched/deadline: Remove unnecessary condition in push_dl_task()

[Juri Lelli]

Hi,

On 18/05/17 11:00, Byungchul Park wrote:
> On Fri, May 12, 2017 at 10:05:59AM +0900, Byungchul Park wrote:
> > pick_next_pushable_dl_task(rq) has BUG_ON(rq->cpu != task_cpu(task))
> > when it returns a task other than NULL, which means that task_cpu(task)
> > must be rq->cpu. So if task == next_task, then task_cpu(next_task) must
> > be rq->cpu as well. Remove the redundant condition and make code simpler.
> > 
> > By this patch, unnecessary one branch and two LOAD operations in 'if'
> > statement can be avoided.
> 
> +cc rostedt@goodmis.org
> +cc juri.lelli@arm.com
> +cc bristot@redhat.com
> 
> > 
> > Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> > Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > Reviewed-by: Juri Lelli <juri.lelli@arm.com>

It looked, and still looks, good to me. :)

Thanks,

- Juri

[tip:sched/core] sched/deadline: Remove unnecessary condition in push_dl_task()

[tip-bot for Byungchul Park]

Commit-ID:  a776b968e52895a350d636e6e7fdcb3b10846fa4
Gitweb:     http://git.kernel.org/tip/a776b968e52895a350d636e6e7fdcb3b10846fa4
Author:     Byungchul Park <byungchul.park@lge.com>
AuthorDate: Fri, 12 May 2017 10:05:59 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 23 May 2017 10:01:33 +0200

sched/deadline: Remove unnecessary condition in push_dl_task()

pick_next_pushable_dl_task(rq) has BUG_ON(rq->cpu != task_cpu(task))
when it returns a task other than NULL, which means that task_cpu(task)
must be rq->cpu. So if task == next_task, then task_cpu(next_task) must
be rq->cpu as well. Remove the redundant condition and make the code simpler.

This way one unnecessary branch and two LOAD operations can be avoided.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Juri Lelli <juri.lelli@arm.com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: <kernel-team@lge.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1494551159-22367-1-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/deadline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a2ce590..df6c291 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1533,7 +1533,7 @@ retry:
 		 * then possible that next_task has migrated.
 		 */
 		task = pick_next_pushable_dl_task(rq);
-		if (task_cpu(next_task) == rq->cpu && task == next_task) {
+		if (task == next_task) {
 			/*
 			 * The task is still there. We don't try
 			 * again, some other cpu will pull it when ready.