Re: [Qemu-devel] [QEMU PATCH 0/3] versioned CPU models / per-machine-type aliases

[Andreas Färber]

Am 26.07.2012 15:53, schrieb Eduardo Habkost:
> On Wed, Jul 25, 2012 at 06:43:25PM -0500, Anthony Liguori wrote:
>> Eduardo Habkost <address@hidden> writes:
>>
>>> Hi,
>>>
>>> This is the first try at a simple system to make the CPU model definitions
>>> versioned (to allow them to get bug fixes while allowing migration from 
>>> older
>>> versions and keeping command-line compatibility), and per- machine-type 
>>> aliases
>>> for compatibility.
>>>
>>> The lack of CPU model versioning is blocking multiple bug fixes that are
>>> necessary on CPU model definitions, but can't be included today because they
>>> would break migration.
>>>
>>> Later, after this gets in (or at least gets some feedback), I plan to send a
>>> proposal for a machine-friendly CPU feature / CPU model probing interface 
>>> that
>>> libvirt could use.
>>
>> This isn't the right approach.  The CPU properties should be exposed as
>> QOM properties which then allows the machine type globals to be used to
>> control stuff like this.
> 
> I would like to use global properties for this, but the obstacles I have
> found were:
> 
> - As far as I can see in the code, global properties are usable only by
>   qdev objects, and CPUs were not qdevfied yet

After Hackweek I plan to put together some compromise or even multiple
alternatives. We definitely need this for multiple open issues.

> - The per-machine-type properties I need to set are for CPU models, not
>   CPUs.
>   - For example: if we fix the Nehalem CPU model by changing the "level"
>     field, we need to make the pc-1.1 and lower machine-types to keep
>     the old "level" value, but only on the Nehalem CPU model

Is that part crying for CPU subclasses? Or what is the problem there?
(Still have a mail about -cpudef in my drafts folder, need to post RFC.)

Andreas

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