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Re: [Qemu-devel] [PATCH for-2.9 15/17] target-i386: Define static "base"


From: David Hildenbrand
Subject: Re: [Qemu-devel] [PATCH for-2.9 15/17] target-i386: Define static "base" CPU model
Date: Tue, 20 Dec 2016 17:49:32 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1

Am 16.12.2016 um 17:02 schrieb Jiri Denemark:
On Mon, Dec 05, 2016 at 21:57:45 -0200, Eduardo Habkost wrote:
On Mon, Dec 05, 2016 at 07:18:47PM +0100, David Hildenbrand wrote:
Am 02.12.2016 um 22:18 schrieb Eduardo Habkost:
The query-cpu-model-expand QMP command needs at least one static
model, to allow the "static" expansion mode to be implemented.
Instead of defining static versions of every CPU model, define a
"base" CPU model that has absolutely no feature flag enabled.


Introducing separate ones makes feature lists presented to the user much
shorter (and therefore easier to maintain). But I don't know how libvirt
wants to deal with models on x86 in the future.

I understand that having a larger set of static models would make
expansions shorter. But I worry that by defining a complete set
of static models on x86 would require extra maintenance work on
the QEMU side with no visible benefit for libvirt.

I would like to hear from libvirt developers what they think. I
still don't know what they plan to use the type=static expansion
results for.

Currently we are mostly interested in the expansion of the "host" CPU
model. We're fine with the expansion based on the "basic" static model
with no features. Returning some real model instead of "basic" would be
OK as long as it would be one of the existing CPU models. Adding special
static models, such as Broadwell-base would actually be a complication

I agree, mixing names would be confusing. So if we would want to introduce static CPU models for x86 in QEMU, they would have to be named
exactly like the libvirt models and contain the exact same feature set.

since we would need to provide some translation to the existing models
for backward compatibility. I'd appreciate if we could avoid doing this.

Right and translation would only confuse people, especially if the CPU
models in libvirt and QEMU behave differently.


Jirka



--

David



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