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Re: [Xen-devel] [PATCH v6 05/11] pvqspinlock, x86: Allow unfair spinlock in a PV guest

Il 14/03/2014 09:30, Peter Zijlstra ha scritto:
Take the situation of 3 (v)CPUs where cpu0 holds the lock but is
preempted. cpu1 queues, cpu2 queues. Then cpu1 gets preempted, after
which cpu0 gets back online.

The simple test-and-set lock will now let cpu2 acquire. Your queue
however will just sit there spinning, waiting for cpu1 to come back from

I think you're way over engineering this. Just do the simple
test-and-set lock for virt && !paravirt (as I think Paolo Bonzini
suggested RHEL6 already does).



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