Re: [Qemu-devel] [PATCH RFC 0/8] cpus: make "-cpu cpux, features" global properties

[Jiri Denemark <jdenemar@redhat.com>]

On Thu, Jun 02, 2016 at 22:44:49 +0200, David Hildenbrand wrote:
> > Current CLI option -cpu cpux,features serves as template
> > for all created cpus of type: cpux. However QEMU parses
> > "features" every time it creates a cpu instance and applies
> > them to it while doing parsing.
> > 
> > That doesn't work well with -device/device_add infrastructure
> > as it has no idea about cpu specific hooks that's used for
> > parsing "features".
> > In order to make -device/device_add utilize "-cpu features"
> > template convert it into a set of global properties, so that
> > every new CPU created will have them applied automatically.
> > 
> > That also allows to parse features only once, instread of
> > doing it for every CPU instance created.
> 
> While I think this makes sense for most cases, we (s390x) are
> currently working on a mechanism to compare and baseline cpu models via
> a qmp interface, to not have to replicate CPU models in libvirt
> every time we do some changes.

BTW, we don't replicate any change to QEMU CPU models in libvirt. We
merely add new CPU models that match the current QEMU definition.
Existing CPU models are never changed. And while the CPU models are
currently used to check compatibility with host CPU, we will stop doing
that in the near future and our CPU models will mostly be used for
detecting what the host CPU is.

Jirka