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

[Jiri Denemark]

On Wed, Jun 22, 2016 at 09:54:51 +0200, David Hildenbrand wrote:
> > 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.

Yeah, I think it's the safest and easiest option now.

Jirka