Re: [Qemu-devel] [PATCH] Add definitions for current cpu models..

[Blue Swirl <blauwirbel@gmail.com>]

On Thu, Jan 21, 2010 at 2:39 PM, Andre Przywara <andre.przywara@amd.com> wrote:
> john cooper wrote:
>>
>> Chris Wright wrote:
>>>
>>> * Daniel P. Berrange (berrange@redhat.com) wrote:
>>>>
>>>> To be honest all possible naming schemes for '-cpu <name>' are just as
>>>> unfriendly as each other. The only user friendly option is '-cpu host'.
>>>> IMHO, we should just pick a concise naming scheme & document it. Given
>>>> they are all equally unfriendly, the one that has consistency with
>>>> vmware
>>>> naming seems like a mild winner.
>>>
>>> Heh, I completely agree, and was just saying the same thing to John
>>> earlier today.  May as well be -cpu {foo,bar,baz} since the meaning for
>>> those command line options must be well-documented in the man page.
>>
>> I can appreciate the concern of wanting to get this
>> as "correct" as possible.  But ultimately we just
>> need three unique tags which ideally have some relation
>> to their associated architectures.  The diatribes
>> available from /proc/cpuinfo while generally accurate
>> don't really offer any more of a clue to the model
>> group, and in their unmodified form are rather unwieldy
>> as command line flags.
>
> I agree. I'd underline that this patch is for migration purposes only, so
> you don't want to specify an exact CPU, but more like a class of CPUs. If
> you look into the available CPUID features in each CPU, you will find that
> there are only a few groups, with currently three for each vendor being a
> good guess.
> /proc/cpuinfo just prints out marketing names, which have only a mild
> relationship to a feature-related technical CPU model. Maybe we can use a
> generation approach like the AMD Opteron ones for Intel, too.
> These G1/G2/G3 names are just arbitrary and have no roots within AMD.
>
> I think that an exact CPU model specification is out of scope for this patch
> and maybe even for QEMU. One could create a database with CPU names and
> associated CPUID flags and provide an external tool to generate a QEMU
> command line out of this. Keeping this database up-to-date (especially for
> desktop CPU models) is a burden that the QEMU project does not want to bear.
>
>>
>>> This is from an EVC kb article[1]:
>>
>> Here is a pointer to a more detailed version:
>>
>>
>> http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003212
>>
>>
>> We probably should also add an option to dump out the
>> full set of qemu-side cpuid flags for the benefit of
>> users and upper level tools.
>
> You mean like this one?
> http://lists.gnu.org/archive/html/qemu-devel/2009-09/msg01228.html
> Resending this patch set is on my plan for next week. What is the state of
> this patch? Will it go in soon? Then I'd rebase my patch set on top of it.

FYI, a similar CPU flag mechanism has been implemented for Sparc and
x86, unifying these would be cool.