Messages in this thread | | | Subject | Re: [PATCH] sched: At sched_fork use __set_task_cpu(). | From | Peter Zijlstra <> | Date | Wed, 01 Feb 2012 14:55:27 +0100 |
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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) > > > > > > -- >
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