[libvirt] What is the strategy to update the CPU Models in src/cpu/cpu_map.xml based on?

Jiri Denemark jdenemar at redhat.com
Wed May 30 11:08:24 UTC 2018


On Wed, May 30, 2018 at 18:55:02 +0800, Dou Liyang wrote:
> Hi Jiri,
> 
> At 05/30/2018 06:14 PM, Jiri Denemark wrote:
> > [Dropping random people from Cc]
> > 
> > On Wed, May 30, 2018 at 18:00:56 +0800, Dou Liyang wrote:
> >> Hi All,
> >>
> >> I am not sure about the update strategy of CPU models in libvirt.
> >>
> >> IMO, It's depend on the CPU model in qemu-kvm, if some CPU models
> >> were updated in qemu-kvm. Then, we should modify the src/cpu/cpu_map.xml
> >> of libvirt to synchronize?
> > 
> > No, we never change existing CPU models in cpu_map.xml to make sure the
> > same CPU model is the same across libvirt versions. Not to mention that
> > QEMU only changes existing CPU models for new machine type (for the same
> > compatibility reason) so we can't just change our CPU models since we
> > don't know what machine type their going to be used with. Libvirt will
> > handle the differences in runtime by remembering any additionally
> > enabled or disabled features once domain starts to make sure the exact
> > same CPU is recreated after, e.g., migration.
> > 
> 
> I see.
> 
> Btw, If we found there is a wrong feature in the existing CPU models,
> what should we do?

What do you mean by wrong feature?

> If we add a new CPU model, what we refer to? CPU models spec or
> hypervisors' code(eg, qemu-kvm)

QEMU code for CPU model and if new CPUID features are required for that
model the CPU vendor's specification of the new features is useful too.

Jirka




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