Re: [Qemu-devel] [RFC 00/28] s390x CPU models: exposing features

[David Hildenbrand <dahi@linux.vnet.ibm.com>]

> On Wed, Jun 22, 2016 at 09:34:49 +0200, David Hildenbrand wrote:
> > I think the coffee didn't do its work already :) . I wanted to write that we can
> > _with_ this additional query. Meaning the involved overhead would be ok - in my
> > opinion for s390x.
> > 
> > What we could do to avoid one compare operation would be:
> > 
> > a) Expand the host model
> > b) Expand the target model (because on s390x we could have migration unsafe
> > model)
> > c) Work with the runnability information returned via query-cpu-definitions
> > 
> > But as we have to do b) either way on s390x, we can directly do a compare
> > operation. (which makes implementation a lot simpler, because libvirt then
> > doesn't have to deal with any feature/model names).  
> 
> But why do you even need to do any comparison? Isn't it possible to let
> QEMU do it when a domain starts? The thing is we should avoid doing
> completely different things on each architecture.
> 

Sure, QEMU will of course double check when starting the guest! So trying to
start and failing is of course an option! So no check is needed if that is
acceptable.

David