Re: [Qemu-devel] [libvirt] [PATCH 0/9] i386: query-cpu-model-expansion test script

[David Hildenbrand]

Am 19.01.2017 um 18:45 schrieb Daniel P. Berrange:
> On Thu, Jan 19, 2017 at 06:21:22PM +0100, David Hildenbrand wrote:
>>
>>>> Also think about "query-cpu-model-expansion model=host type=static",
>>>> which will primarily be used by libvirt on s390x. There is no way to
>>>> expand this into a static cpu model. Faking anything will just hide errors.
>>>
>>> Yes, static expansion of host model must always return an error
>>> if it's not possible to expand.
>>>
>>>>
>>>> If "host" can't be expanded, QEMU has to be treated like there is no CPU
>>>> model support (as for older QEMU versions).
>>>
>>> OK. I will propose a patch updating the query-cpu-model-expansion
>>> documentation to be more explicit about it.
>>
>> The only real alternative I see would be disabling the query-cpu-model-*
>> interface completely if KVM support is not available.
>>
>> This would however mean, that the same QEMU binary would have the
>> interface when running under TCG, but not when running under KVM on an
>> old KVM version.
>>
>> That also doesn't really feel right, or what do you think?
> 
> Yeah that really isn't good.  query-cpu-model-* needs to work on TCG
> and *not* have a dependancy on KVM in that case, since you can be
> running TCG s390 on a x86_64 host, so the host CPU is totally irrelevant
> for TCG
> 

Actually what I meant was:

TCG: query-cpu-model-* interface always provided
KVM (with cpu model support): query-cpu-model-* interface provided
KVM (without cpu model support): no query-cpu-model-* interface provided

This would avoid having to report an error when expanding "host" in the
third case (KVM without cpu model support) but would lead to one QEMU
binary having a different set of supported qmp calls when called from
TCG and KVM.

> Regards,
> Daniel
> 


-- 

David