Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

[Arjan van de Ven]

On 10/2/2013 5:45 AM, Frederic Weisbecker wrote:
> On Tue, Oct 01, 2013 at 06:59:57PM +0200, Peter Zijlstra wrote:
> > On Tue, Oct 01, 2013 at 06:47:10PM +0200, Frederic Weisbecker wrote:
> > > Yeah thinking more about it, the preempt disable was probably not
> > > necessary. Now that's trading 2 atomics + 1 Lock/Unlock with 2 Lock/Unlock.
> >
> > It trades the current 2 atomics for 2 LOCK/UNLOCK. And on x86_64 that's
> > 2 atomics.
>
> Do you mean 2 atomics for LOCK/UNLOCK? Or is that pair optimized somehow
> in x86?

unlock is not actually an atomic.

and on some modern machines, neither is the lock, for the uncontended case ;-)

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