Re: [tip:timers/nohz] nohz: Move full nohz kick to its own IPI

[Frederic Weisbecker]

On Mon, May 05, 2014 at 05:12:28PM +0200, Peter Zijlstra wrote:
> > Note the current ordering:
> > 
> >     cmpxchg(&qsd->pending, 0, 1)       get ipi
> >     csd_lock(qsd->csd)                 xchg(&qsd->pending, 1)
> >     send ipi                           csd_unlock(qsd->csd)
> > 
> > 
> > So there shouldn't be racing updaters. Also ipi sender shouldn't
> > race with ipi receiver, the update shouldn't always eventually see
> > the unlock happening.
> 
> Yeah, I've not spotted how this particular train wreck happens either.
> 
> The problem is reproduction, it took me 9 hours to confirm I could
> reproduce the problem on my machine. So how long to I run it with this
> patch reverted to show its gone..

Maybe it could be favoured cpu hotplug. Anyway converting to irq_work should
fix it.
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