Re: [Qemu-devel] [Patch v1 00/29] s390x CPU models: exposing features

[Eduardo Habkost]

On Tue, Aug 02, 2016 at 01:58:46PM +0200, David Hildenbrand wrote:
[...]
> So we have:
> a) "query-cpu-model-expansion" - tell us what the "host" or another CPU
>    model looks like. Either falling back to a static model or
>    completely exposing all properties.

The query-cpu-model-expansion interface looks good to me. I just
had a few comments about the interface documentation.

> b) "query-cpu-model-comparison" - tell us how two CPU models compare,
>     indicating which properties were responsible for the decision.
> c) "query-cpu-model-baseline" - create a new model out of two models,
>     taking a requested level of stability into account.

I miss a clearer specifiction of what are the actual requirements
and use cases of query-cpu-model-baseline. Is it related to
runnability? If so, how exactly?

Related to that (as mentioned in my reply to patch 25/29), I
would like a clearer definintion of what "superset" and "subset"
mean exactly, in query-cpu-model-comparison. Likewise, I would
like to understand the requirements and use cases that make
"superset" and "subset" useful.

> 
> --------------------------------Libvirt usecase----------------------------
> 
> Testing for runability:
> - Simply try to start QEMU with KVM, compat machine, CPU model
> - Could be done using query-cpu-model-comparison in the future.
> 
> Identifying host model, e.g. "virsh capabilities"
> - query-cpu-model-expansion on "host" with "-M none --enable-kvm"
> 
> <cpu mode='host-model'>:
> - simply copy the identified host model

AFAICS, this will work out of the box only if
  query-cpu-model-expansion {name: "host"}
return a static CPU model name in return.model.name.

> 
> <cpu mode='host-passthrough'>:
> - "-cpu host"
> 
> "virsh cpu-baseline":
> - query-cpu-model-baseline on two models with "-M none"
> 
> "virsh cpu-compare":
> - query-cpu-model-comparison on two models with "-M none"
> 
> There might be some cenarios where libvirt wants to convert another CPU
> model to a static variant, this can be done using query-cpu-model-expansion
> 
[...]

-- 
Eduardo