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

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

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Rik van Riel <riel@xxxxxxxxxx>

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Sat, 22 Jan 2011 09:53:46 -0500

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Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Américo , Nick Piggin <npiggin@xxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, suzuki@xxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, Wang <xiyou.wangcong@xxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>

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On 01/22/2011 01:14 AM, Srivatsa Vaddagiri wrote:

Also it may be possible for the pv-ticketlocks to track owning vcpu and make use
of a yield-to interface as further optimization to avoid the
"others-get-more-time" problem, but Peterz rightly pointed that PI would be a
better solution there than yield-to. So overall IMO kvm_vcpu_on_spin+yield_to
could be the best solution for unmodified guests, while paravirtualized
ticketlocks + some sort of PI would be a better solution where we have the
luxury of modifying guest sources!


Agreed, for unmodified guests (which is what people will mostly be
running for the next couple of years), we have little choice but
to use PLE + kvm_vcpu_on_spin + yield_to.

The main question that remains is whether the PV ticketlocks are
a large enough improvement to also merge those.  I expect they
will be, and we'll see so in the benchmark numbers.

--
All rights reversed

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