[PATCH v3 1/2] sched/deadline: Remove unnecessary condition in push_dl_task()

[PATCH v3 1/2] 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>
---
 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

[PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

[Byungchul Park]

pick_next_pushable_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>
---
 kernel/sched/rt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4101f9d..5abd9a52 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1820,7 +1820,7 @@ static int push_rt_task(struct rq *rq)
 		 * pushing.
 		 */
 		task = pick_next_pushable_task(rq);
-		if (task_cpu(next_task) == rq->cpu && task == next_task) {
+		if (task == next_task) {
 			/*
 			 * The task hasn't migrated, and is still the next
 			 * eligible task, but we failed to find a run-queue
-- 
1.9.1

Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

[Steven Rostedt]

On Thu, 16 Feb 2017 11:34:17 +0900
Byungchul Park <byungchul.park@lge.com> wrote:

> pick_next_pushable_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>
> ---

This is a different patch, I don't believe Juri reviewed it yet.

-- Steve

Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

[Byungchul Park]

On Wed, Feb 15, 2017 at 09:45:37PM -0500, Steven Rostedt wrote:
> On Thu, 16 Feb 2017 11:34:17 +0900
> Byungchul Park <byungchul.park@lge.com> wrote:
> 
> > pick_next_pushable_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>
> > ---
> 
> This is a different patch, I don't believe Juri reviewed it yet.

I will take care not to make this kind of mistake next time.

Thank you very much.

> 
> -- Steve

RE: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

[byungchul.park]

> -----Original Message-----
> From: Steven Rostedt [mailto:rostedt@goodmis.org]
> Sent: Thursday, February 16, 2017 11:46 AM
> To: Byungchul Park
> Cc: peterz@infradead.org; mingo@kernel.org; linux-kernel@vger.kernel.org;
> juri.lelli@gmail.com; kernel-team@lge.com
> Subject: Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in
> push_rt_task()
> 
> On Thu, 16 Feb 2017 11:34:17 +0900
> Byungchul Park <byungchul.park@lge.com> wrote:
> 
> > pick_next_pushable_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>
> > ---
> 
> This is a different patch, I don't believe Juri reviewed it yet.

Hello juri,

I should have asked you first and been more careful before I added
'reviewed-by'. Can I ask you for your opinion about the additional one?

Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

[Juri Lelli]

Hi,

On 16/02/17 16:15, byungchul.park wrote:
> > -----Original Message-----
> > From: Steven Rostedt [mailto:rostedt@goodmis.org]
> > Sent: Thursday, February 16, 2017 11:46 AM
> > To: Byungchul Park
> > Cc: peterz@infradead.org; mingo@kernel.org; linux-kernel@vger.kernel.org;
> > juri.lelli@gmail.com; kernel-team@lge.com
> > Subject: Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in
> > push_rt_task()
> > 
> > On Thu, 16 Feb 2017 11:34:17 +0900
> > Byungchul Park <byungchul.park@lge.com> wrote:
> > 
> > > pick_next_pushable_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>
> > > ---
> > 
> > This is a different patch, I don't believe Juri reviewed it yet.
> 
> Hello juri,
> 
> I should have asked you first and been more careful before I added
> 'reviewed-by'. Can I ask you for your opinion about the additional one?
> 

Looks good to me, you can leave my Reviewed-by.

Steve, thanks for pointing out that I didn't yet reviewed it. :)

Thanks,

- Juri

Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

[Daniel Bristot de Oliveira]

On 02/16/2017 03:34 AM, Byungchul Park wrote:
> pick_next_pushable_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>

+1

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>

-- Daniel

Re: [PATCH v3 1/2] sched/deadline: Remove unnecessary condition in push_dl_task()

[Daniel Bristot de Oliveira]

On 02/16/2017 03:34 AM, 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.
> 
> 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>

+1

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>

-- Daniel

Re: [PATCH v3 1/2] sched/deadline: Remove unnecessary condition in push_dl_task()

[Byungchul Park]

On Thu, Feb 16, 2017 at 06:35:54PM +0100, Daniel Bristot de Oliveira wrote:
> On 02/16/2017 03:34 AM, 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.
> > 
> > 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>
> 
> +1
> 
> Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>

Hello,

Could you check this out?

> 
> -- Daniel

Re: [PATCH v3 1/2] sched/deadline: Remove unnecessary condition in push_dl_task()

[Byungchul Park]

On Thu, Feb 16, 2017 at 11:34:16AM +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.

Hello,

What do you think?

> 
> 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>
> ---
>  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: [PATCH v3 1/2] sched/deadline: Remove unnecessary condition in push_dl_task()

[Byungchul Park]

On Thu, Feb 16, 2017 at 11:34:16AM +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.
> 
> 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>

Hello,

These two patches remove definitely unnecessary condition statements.
Please review it.

Thanks,
Byungchul

> ---
>  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