Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()"locks up on ARM

[Santosh Shilimkar]

Peter,

On 5/26/2011 10:53 PM, Peter Zijlstra wrote:
> On Thu, 2011-05-26 at 19:17 +0200, Peter Zijlstra wrote:
> > On Thu, 2011-05-26 at 19:04 +0200, Oleg Nesterov wrote:
> > > On 05/26, Peter Zijlstra wrote:
> > > > @@ -2636,7 +2636,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
> > > >   		 * to spin on ->on_cpu if p is current, since that would
> > > >   		 * deadlock.
> > > >   		 */
> > > > -		if (p == current) {
> > > > +		if (cpu == smp_processor_id()) {
> > > > +			p->sched_contributes_to_load = 0;
> > > >   			ttwu_queue(p, cpu);
> > >
> > > Btw. I do not pretend I really understand se->vruntime, but in this
> > > case we are doing enqueue_task() without ->task_waking(), however we
> > > pass ENQUEUE_WAKING. Is it correct?
> >
> > No its not, that's the thing that I got wrong the first time and caused
> > these pauses.
>
> We'd end up with something like the below, which isn't too different
> from what I've now got queued.
>
> It has the extra cpu == smp_processor_id() check, but I'm not sure this
> whole case is worth the trouble. I could go stick some counters in to
> verify how often all this happens I guess.
Are you planning send version of this patch for stable .39
too ?

Regards
Santosh
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