Re: Spinlocks: Factor our GENERIC_LOCKBREAK in order to avoid spinwith irqs disable

[Jeremy Fitzhardinge]

Nick Piggin wrote:
> Sure. Btw. I have no problems with your patchset, but if SMP guests
> are seriously used on x86, just remember the fairness issue. At some
> point you might find you'll need an even more advanced lock for Xen.
>   

Perhaps.  The spin lock has a bounded number of iterations before it 
goes into the vcpu-blocking path.  At that point, it's no longer subject 
to the whims of the cache coherency protocol, and is explicitly woken.  
But it may still have issues when competing with a rapid lock-unlocker.

A ticket-lock variant with some kind of directed yield might be the way 
to go if it turns out to be a problem.

   J
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