[Xen-devel] Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Wed, 2011-01-19 at 22:53 +0530, Srivatsa Vaddagiri wrote:
> On Wed, Jan 19, 2011 at 10:42:39PM +0530, Srivatsa Vaddagiri wrote:
> > Add two hypercalls to KVM hypervisor to support pv-ticketlocks.
> > 
> > KVM_HC_WAIT_FOR_KICK blocks the calling vcpu until another vcpu kicks it or 
> > it
> > is woken up because of an event like interrupt.
> 
> One possibility is to extend this hypercall to do a directed yield as well, 
> which needs some more thought. Another issue that needs to be resolved with
> pv-ticketlocks is the impact on intra-VM fairness. A guest experiencing heavy
> contention can keep yielding cpu, allowing other VMs to get more time than 
> they
> deserve.

No, yield sucks, if you know the owner you can do actual PI.

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