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SubjectRe: Spinlocks: Factor our GENERIC_LOCKBREAK in order to avoid spin with irqs disable
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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