Re: [Qemu-devel] [PATCH 3/3] S390: Enable -cpu help and QMP query-cpu-definitions

[Andreas Färber]

Am 12.12.2012 16:05, schrieb Viktor Mihajlovski:
> On 12/12/2012 02:51 PM, Andreas Färber wrote:
>>> +    (*cpu_fprintf)(f, "s390 %16s\n", "[host]");
>>
>> Note that the square-bracket notation was specific to x86 when it
>> distinguished between built-in and config-based models.
>>
> OK, since libvirt capable of dealing with s390 cpu models will
> never see this, we can change it any way that is wanted.
> So, host without brackets?

Yes, but see below...

>> "host" only makes sense for KVM, not for TCG. So we would need one other
>> placeholder model for libvirt.
> see my reply to Alex' comment: the placeholder name must be chosen
> carefully, i.e. future-proof

On further thoughts, didn't we discuss that the issue libvirt wants to
address is that migration from z10 to z9 must fail? That's not solved
with -cpu host, we would need two other models then. IMO ideally -cpu
host should have the same semantics as on x86, that is passing the host
features through mostly 1:1. IIUC there is currently no way to not do so?

What about future-wise having -cpu host not be a subclass and instead
behaving like Alex' -cpu best, given the above semantics? What I am just
worried about with this patch is cementing the use of -cpu host into
libvirt when that is not a mid-term solution.

Andreas

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