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

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

Il 17/03/2014 19:54, Peter Zijlstra ha scritto:
> On Mon, Mar 17, 2014 at 01:44:34PM -0400, Waiman Long wrote:
> > The PV ticketlock code was designed to handle lock holder preemption by
> > redirecting CPU resources in a preempted guest to another guest that can
> > better use it and then return the preempted CPU back sooner.
> But that's the PV code, not the unfair bit. And your fuller PV thing
> doesn't need the unfair option.
I agree.  You need three cases:

* non-virt, non-PV: regular qspinlock

* virt (X86_FEATURE_HYPERVISOR), non-PV: test-and-set

* virt, PV: disables test-and-set, adds PV waiting to qspinlock

Paolo

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