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

To: vatsa@xxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed, 19 Jan 2011 18:50:15 +0100
Cc: Mathieu, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, Jeremy, Linux, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Beulich <JBeulich@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan, Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, suzuki@xxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, "H. Peter Anvin" <hpa@xxxxxxxxx>, Américo Wang <xiyou.wangcong@xxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
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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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