[openstack-dev] [nova][libvirt] The None and 'none' for CONF.libvirt.cpu_mode

Daniel P. Berrange berrange at redhat.com
Wed Mar 4 17:56:19 UTC 2015

On Wed, Mar 04, 2015 at 05:24:53PM +0000, Jiang, Yunhong wrote:
> Daniel, thanks for your clarification.
> Another related question is, what will be the guest's real cpu model
> is the cpu_model is None? This is about a reported regression at

The guest CPU will be unspecified - it will be some arbitrary
hypervisor decided default which nova cannot know.

> https://bugs.launchpad.net/nova/+bug/1082414 . When the
> instance.vcpu_model.mode is None, we should compare the source/target
> cpu model, as the suggestion from Tony, am I right?

If CPU model is none, best we can do is compare the *host* CPU of
the two hosts to make sure the host doesn't loose any features, as
we have no way of knowing what features the guest is relying on.

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