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

[Dor Laor <dlaor@redhat.com>]

On 01/21/2010 05:05 PM, Anthony Liguori wrote:
> On 01/20/2010 07:18 PM, 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.
>
> This is the root of the trouble. At the qemu layer, we try to focus on
> being correct.
>
> Management tools are typically the layer that deals with being "correct".
>
> A good compromise is making things user tunable which means that a
> downstream can make "correctness" decisions without forcing those
> decisions on upstream.
>
> In this case, the idea would be to introduce a new option, say something
> like -cpu-def. The syntax would be:
>
> -cpu-def
> name=coreduo,level=10,family=6,model=14,stepping=8,features=+vme+mtrr+clflush+mca+sse3+monitor,xlevel=0x80000008,model_id="Genuine
> Intel(R) CPU T2600 @ 2.16GHz"
>
> Which is not that exciting since it just lets you do -cpu coreduo in a
> much more complex way. However, if we take advantage of the current
> config support, you can have:
>
> [cpu-def]
> name=coreduo
> level=10
> family=6
> model=14
> stepping=8
> features="+vme+mtrr+clflush+mca+sse3.."
> model_id="Genuine Intel..."
>
> And that can be stored in a config file. We should then parse
> /etc/qemu/target-<targetname>.conf by default. We'll move the current
> x86_defs table into this config file and then downstreams/users can
> define whatever compatibility classes they want.
>
> With this feature, I'd be inclined to take "correct" compatibility
> classes like Nehalem as part of the default qemurc that we install
> because it's easily overridden by a user. It then becomes just a
> suggestion on our part verses a guarantee.
>
> It should just be a matter of adding qemu_cpudefs_opts to
> qemu-config.[ch], taking a new command line that parses the argument via
> QemuOpts, then passing the parsed options to a target-specific function
> that then builds the table of supported cpus.

Isn't the outcome of John's patches and these configs will be exactly 
the same? Since these cpu models won't ever change, there is no reason 
why not to hard code them. Adding configs or command lines is a good 
idea but it is more friendlier to have basic support to the common cpus.
This is why qemu today offers: -cpu ?
x86           qemu64
x86           phenom
x86         core2duo
x86            kvm64
x86           qemu32
x86          coreduo
x86              486
x86          pentium
x86         pentium2
x86         pentium3
x86           athlon
x86             n270

So bottom line, my point is to have John's base + your configs. We need 
to keep also the check verb and the migration support for sending those.

btw: IMO we should deal with this complexity ourselves and save 99.9% of 
the users the need to define such models, don't ask this from a java 
programmer, he is running on a JVM :-)


>
> Regards,
>
> Anthony Liguori
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