openstack team mailing list archive

[Christoph Hellwig <Christoph.Hellwig@xxxxxxxxxx>]

On Tue, 2012-05-08 at 16:08 -0400, Lorin Hochstein wrote:
> Are there any Nova features that work with KVM but don't work with
> QEMU? Either way, I'd like to capture this in the documentation
> 
> I know that KVM is faster than QEMU because of hardware support, but I
> don't know if there's additional functionality that only works with
> KVM. The Hypervisor support matrix wiki page
> <http://wiki.openstack.org/HypervisorSupportMatrix> has no specific
> information on OpenStack features supported by KVM but not QEMU

The first question is what do you mean with KVM?  Any qemu binary using
kernel acceleration by using the kvm kernel module, or using the
qemu-kvm fork that's slowly getting merged back into qemu mainline (it's
down to about 5000 LOC difference now) in either kvm or tcq mode?

There should be no feature difference between using hardware accelerated
KVM mode, and TCG emulation, unless you call boots a reasonable cloud in
your lifetime a feature, or if you look the other way around running
foreign architecture OS images, which is something KVM can't do.

There are features not merged back into mainline qemu, with device
assignment being the last one in current mainline, and MSI(X) and the
I/O thread support others in common released versions.  In theory these
also should work using TCG in qemu-kvm, although it's very unlikely to
be tested very well.