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

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  [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task() Byungchul Park <byungchul.park@lge.com> - 2017-02-16 03:40 +0100
    Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in  push_rt_task() Steven Rostedt <rostedt@goodmis.org> - 2017-02-16 03:50 +0100
      Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in  push_rt_task() Byungchul Park <byungchul.park@lge.com> - 2017-02-16 04:10 +0100
      RE: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task() "byungchul.park" <byungchul.park@lge.com> - 2017-02-16 08:20 +0100
        Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in  push_rt_task() Juri Lelli <juri.lelli@arm.com> - 2017-02-16 09:50 +0100
    Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in  push_rt_task() Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-02-16 18:40 +0100

#1582275 — [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

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

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#1582284 — 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.

-- Steve

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#1582293 — Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

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

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#1582364

> -----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?

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#1582384 — Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

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

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#1582726 — Re: [PATCH v3 2/2] sched/rt: Remove unnecessary condition in push_rt_task()

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

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