Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box

[Andreas Färber]

Am 27.08.2014 17:42, schrieb Eduardo Habkost:
> On Wed, Aug 27, 2014 at 04:33:54PM +0200, Paolo Bonzini wrote:
>> Il 27/08/2014 16:05, Eduardo Habkost ha scritto:
>>> On Wed, Aug 27, 2014 at 03:36:51PM +0200, Paolo Bonzini wrote:
>>>> Il 26/08/2014 20:01, Eduardo Habkost ha scritto:
>>>>> So maybe that's good news, as things can be simpler if we make both TCG
>>>>> and KVM have similar behavior:
>>>>>
>>>>> * qemu64: a conservative default that should work out of the box on
>>>>>   most systems, for both TCG and KVM. That's already the current status,
>>>>>   we just need to document it.
>>>>>
>>>>> * -cpu host: for people who want every possible feature to be enabled
>>>>>   (but without cross-version live-migration support). We can easily add
>>>>>   support for "-cpu host" to TCG, too.
>>>>
>>>> This means that "-cpu host" has different meanings in KVM and TCG.  Is
>>>> that an advantage or a disadvantage?
>>>
>>> It is the same meaning to me: "enable everything that's possible,
>>> considering what's provided by the underlying accelerator". The "host"
>>> name is misleading, though, because on KVM it is close to the host CPU,
>>> but on TCG it depends solely on TCG's capabilities.
>>
>> True.  It's not very intuitive, but it is the same concept for processor
>> capabilities.
>>
>> Though for some leaves that do not correspond to processor capabilities,
>> "-cpu host" does set them to the host values.  This is not just the
>> cache model, but also the family/model/stepping/vendor.
>>
>> For the TCG case, when running on a Nehalem it would be weird to see a
>> Nehalem guest with SMAP or ADOX support...  I'm not sure it would even
>> work to have SVM with an Intel vendor. :)
> 
> In that case, the best family/model/stepping/vendor choice depends on
> TCG capabilities (defined at compile time), not on the host CPU.
> 
> ...and that proves your point: if we aren't even using the host CPU
> family/model/stepping, calling it "-cpu host" doesn't make much sense.
> If it is so different from the host model, we can call it "qemu64" (and
> do as you suggests below).

Might that be an opportunity to reconsider a -cpu best or so,
independent of its implementation, to avoid "host"?

Regards,
Andreas

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