* [PATCH] sched: remove an unnecessary memory access, rq->cpu in __schedule()
@ 2016-02-11 2:59 Byungchul Park
2016-02-17 8:31 ` Ingo Molnar
2016-02-17 12:14 ` [tip:sched/core] sched/core: Remove dead statement in __schedule( ) tip-bot for Byungchul Park
0 siblings, 2 replies; 4+ messages in thread
From: Byungchul Park @ 2016-02-11 2:59 UTC (permalink / raw)
To: peterz, mingo; +Cc: linux-kernel
Is there any reason keeping this statement on the code?
-----8<-----
>From d8a387efb8199b69b6464970d6f9fc57cbcf0ab0 Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Thu, 11 Feb 2016 11:50:53 +0900
Subject: [PATCH] sched: remove an unnecessary memory access, rq->cpu in
__schedule()
Remove an unnecessary assignment of variable not used any more.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/sched/core.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1315cec..501f5d9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3193,7 +3193,6 @@ static void __sched notrace __schedule(bool preempt)
trace_sched_switch(preempt, prev, next);
rq = context_switch(rq, prev, next); /* unlocks the rq */
- cpu = cpu_of(rq);
} else {
lockdep_unpin_lock(&rq->lock);
raw_spin_unlock_irq(&rq->lock);
--
1.9.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] sched: remove an unnecessary memory access, rq->cpu in __schedule()
2016-02-11 2:59 [PATCH] sched: remove an unnecessary memory access, rq->cpu in __schedule() Byungchul Park
@ 2016-02-17 8:31 ` Ingo Molnar
2016-02-17 8:48 ` Byungchul Park
2016-02-17 12:14 ` [tip:sched/core] sched/core: Remove dead statement in __schedule( ) tip-bot for Byungchul Park
1 sibling, 1 reply; 4+ messages in thread
From: Ingo Molnar @ 2016-02-17 8:31 UTC (permalink / raw)
To: Byungchul Park; +Cc: peterz, linux-kernel
* Byungchul Park <byungchul.park@lge.com> wrote:
> Is there any reason keeping this statement on the code?
>
> -----8<-----
> From d8a387efb8199b69b6464970d6f9fc57cbcf0ab0 Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul.park@lge.com>
> Date: Thu, 11 Feb 2016 11:50:53 +0900
> Subject: [PATCH] sched: remove an unnecessary memory access, rq->cpu in
> __schedule()
>
> Remove an unnecessary assignment of variable not used any more.
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> kernel/sched/core.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1315cec..501f5d9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3193,7 +3193,6 @@ static void __sched notrace __schedule(bool preempt)
>
> trace_sched_switch(preempt, prev, next);
> rq = context_switch(rq, prev, next); /* unlocks the rq */
> - cpu = cpu_of(rq);
> } else {
> lockdep_unpin_lock(&rq->lock);
> raw_spin_unlock_irq(&rq->lock);
There's no memory access that I can see - GCC will optimize it out.
Having said that, it is a dead statement so can be removed. I fixed the title
accordingly.
Thanks,
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] sched: remove an unnecessary memory access, rq->cpu in __schedule()
2016-02-17 8:31 ` Ingo Molnar
@ 2016-02-17 8:48 ` Byungchul Park
0 siblings, 0 replies; 4+ messages in thread
From: Byungchul Park @ 2016-02-17 8:48 UTC (permalink / raw)
To: Ingo Molnar; +Cc: peterz, linux-kernel
On Wed, Feb 17, 2016 at 09:31:09AM +0100, Ingo Molnar wrote:
>
> * Byungchul Park <byungchul.park@lge.com> wrote:
>
> > Is there any reason keeping this statement on the code?
> >
> > -----8<-----
> > From d8a387efb8199b69b6464970d6f9fc57cbcf0ab0 Mon Sep 17 00:00:00 2001
> > From: Byungchul Park <byungchul.park@lge.com>
> > Date: Thu, 11 Feb 2016 11:50:53 +0900
> > Subject: [PATCH] sched: remove an unnecessary memory access, rq->cpu in
> > __schedule()
> >
> > Remove an unnecessary assignment of variable not used any more.
> >
> > Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> > ---
> > kernel/sched/core.c | 1 -
> > 1 file changed, 1 deletion(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 1315cec..501f5d9 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -3193,7 +3193,6 @@ static void __sched notrace __schedule(bool preempt)
> >
> > trace_sched_switch(preempt, prev, next);
> > rq = context_switch(rq, prev, next); /* unlocks the rq */
> > - cpu = cpu_of(rq);
> > } else {
> > lockdep_unpin_lock(&rq->lock);
> > raw_spin_unlock_irq(&rq->lock);
>
> There's no memory access that I can see - GCC will optimize it out.
Yes, gcc will do it. So I expect no performance effect.
>
> Having said that, it is a dead statement so can be removed. I fixed the title
> accordingly.
Thank you.
>
> Thanks,
>
> Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip:sched/core] sched/core: Remove dead statement in __schedule( )
2016-02-11 2:59 [PATCH] sched: remove an unnecessary memory access, rq->cpu in __schedule() Byungchul Park
2016-02-17 8:31 ` Ingo Molnar
@ 2016-02-17 12:14 ` tip-bot for Byungchul Park
1 sibling, 0 replies; 4+ messages in thread
From: tip-bot for Byungchul Park @ 2016-02-17 12:14 UTC (permalink / raw)
To: linux-tip-commits
Cc: byungchul.park, peterz, tglx, torvalds, linux-kernel, mingo, hpa
Commit-ID: 3223d052b79eb9b620d170584c417d60a8bfd649
Gitweb: http://git.kernel.org/tip/3223d052b79eb9b620d170584c417d60a8bfd649
Author: Byungchul Park <byungchul.park@lge.com>
AuthorDate: Thu, 11 Feb 2016 11:59:38 +0900
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 17 Feb 2016 09:32:03 +0100
sched/core: Remove dead statement in __schedule()
Remove an unnecessary assignment of variable not used any more.
( This has no runtime effects as GCC is smart enough to optimize
this out. )
Signed-off-by: Byungchul Park <byungchul.park@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/1455159578-17256-1-git-send-email-byungchul.park@lge.com
[ Edited the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/core.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7e548bd..87ca0be 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3346,7 +3346,6 @@ static void __sched notrace __schedule(bool preempt)
trace_sched_switch(preempt, prev, next);
rq = context_switch(rq, prev, next); /* unlocks the rq */
- cpu = cpu_of(rq);
} else {
lockdep_unpin_lock(&rq->lock);
raw_spin_unlock_irq(&rq->lock);
^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2016-02-17 12:15 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2016-02-11 2:59 [PATCH] sched: remove an unnecessary memory access, rq->cpu in __schedule() Byungchul Park
2016-02-17 8:31 ` Ingo Molnar
2016-02-17 8:48 ` Byungchul Park
2016-02-17 12:14 ` [tip:sched/core] sched/core: Remove dead statement in __schedule( ) tip-bot for Byungchul Park
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