* [PATCH] sched: At sched_fork use __set_task_cpu().
@ 2012-01-29 16:34 Rakib Mullick
2012-01-31 8:48 ` Kamalesh Babulal
0 siblings, 1 reply; 4+ messages in thread
From: Rakib Mullick @ 2012-01-29 16:34 UTC (permalink / raw)
To: mingo, a.p.zijlstra; +Cc: linux-kernel
We don't use select_task_rq() from sched_fork() anymore and no chance of task gets migrated at
this point. Therefore, we can avoid task migration related checking/accounting, so use
__set_task_cpu() instead of set_task_cpu().
Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df00cb0..a38026e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1755,7 +1755,7 @@ void sched_fork(struct task_struct *p)
* Silence PROVE_RCU.
*/
raw_spin_lock_irqsave(&p->pi_lock, flags);
- set_task_cpu(p, cpu);
+ __set_task_cpu(p, cpu);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] sched: At sched_fork use __set_task_cpu().
2012-01-29 16:34 [PATCH] sched: At sched_fork use __set_task_cpu() Rakib Mullick
@ 2012-01-31 8:48 ` Kamalesh Babulal
2012-02-01 13:55 ` Peter Zijlstra
0 siblings, 1 reply; 4+ messages in thread
From: Kamalesh Babulal @ 2012-01-31 8:48 UTC (permalink / raw)
To: Rakib Mullick; +Cc: mingo, a.p.zijlstra, linux-kernel
* Rakib Mullick <rakib.mullick@gmail.com> [2012-01-29 22:34:37]:
> We don't use select_task_rq() from sched_fork() anymore and no chance of task gets migrated at
> this point. Therefore, we can avoid task migration related checking/accounting, so use
> __set_task_cpu() instead of set_task_cpu().
>
> Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> ---
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index df00cb0..a38026e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1755,7 +1755,7 @@ void sched_fork(struct task_struct *p)
> * Silence PROVE_RCU.
> */
> raw_spin_lock_irqsave(&p->pi_lock, flags);
> - set_task_cpu(p, cpu);
> + __set_task_cpu(p, cpu);
> raw_spin_unlock_irqrestore(&p->pi_lock, flags);
>
> #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
>
>
> --
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] sched: At sched_fork use __set_task_cpu().
2012-01-31 8:48 ` Kamalesh Babulal
@ 2012-02-01 13:55 ` Peter Zijlstra
2012-02-01 17:07 ` Rakib Mullick
0 siblings, 1 reply; 4+ messages in thread
From: Peter Zijlstra @ 2012-02-01 13:55 UTC (permalink / raw)
To: Kamalesh Babulal; +Cc: Rakib Mullick, mingo, linux-kernel
On Tue, 2012-01-31 at 14:18 +0530, Kamalesh Babulal wrote:
> * Rakib Mullick <rakib.mullick@gmail.com> [2012-01-29 22:34:37]:
>
> > We don't use select_task_rq() from sched_fork() anymore and no chance of task gets migrated at
> > this point. Therefore, we can avoid task migration related checking/accounting, so use
> > __set_task_cpu() instead of set_task_cpu().
> >
> > Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
> Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Since we call sched_fork() with preemption enabled _long_ after the
child is copied from the parent who is to say we (parent) didn't migrate
away and are now setting a different cpu?
One could argue that that might not be a real migration from the child's
POV, maybe, but nobody seems to be making that argument.
I really don't see the point of this..
> > ---
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index df00cb0..a38026e 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1755,7 +1755,7 @@ void sched_fork(struct task_struct *p)
> > * Silence PROVE_RCU.
> > */
> > raw_spin_lock_irqsave(&p->pi_lock, flags);
> > - set_task_cpu(p, cpu);
> > + __set_task_cpu(p, cpu);
> > raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> >
> > #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> >
> >
> > --
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] sched: At sched_fork use __set_task_cpu().
2012-02-01 13:55 ` Peter Zijlstra
@ 2012-02-01 17:07 ` Rakib Mullick
0 siblings, 0 replies; 4+ messages in thread
From: Rakib Mullick @ 2012-02-01 17:07 UTC (permalink / raw)
To: Peter Zijlstra; +Cc: Kamalesh Babulal, mingo, linux-kernel
On Wed, Feb 1, 2012 at 7:55 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Tue, 2012-01-31 at 14:18 +0530, Kamalesh Babulal wrote:
>> * Rakib Mullick <rakib.mullick@gmail.com> [2012-01-29 22:34:37]:
>>
>> > We don't use select_task_rq() from sched_fork() anymore and no chance of task gets migrated at
>> > this point. Therefore, we can avoid task migration related checking/accounting, so use
>> > __set_task_cpu() instead of set_task_cpu().
>> >
>> > Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
>> Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
>
> Since we call sched_fork() with preemption enabled _long_ after the
> child is copied from the parent who is to say we (parent) didn't migrate
> away and are now setting a different cpu?
>
If parent gets migrated that should be accounted as parents migration
count not for child offcourse. And if we're counting child's
nr_migration count for parent's getting migrated, we're simply
screwing childs migration count. Isn't it?
> One could argue that that might not be a real migration from the child's
> POV, maybe, but nobody seems to be making that argument.
>
But I'm not seeing it from child's or parent's POV. I'm simply
addressing the point of a task's migration counter
(p->se.nr_migrations), simply this task wasn't moved.
> I really don't see the point of this..
>
I'm hoping, you'll rethink...
Thanks,
Rakib
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2012-02-01 17:07 UTC | newest]
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2012-01-29 16:34 [PATCH] sched: At sched_fork use __set_task_cpu() Rakib Mullick
2012-01-31 8:48 ` Kamalesh Babulal
2012-02-01 13:55 ` Peter Zijlstra
2012-02-01 17:07 ` Rakib Mullick
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