Re: [Qemu-devel] [libvirt] Modern CPU models cannot be used with libvirt

[Avi Kivity]

On 03/25/2012 05:30 PM, Anthony Liguori wrote:
> On 03/25/2012 10:18 AM, Avi Kivity wrote:
>> On 03/25/2012 05:07 PM, Anthony Liguori wrote:
>>>> As log as qemu -nodefconfig -cpu westmere -M pc1.1
>>>
>>>
>>> -nodefconfig is going to eventually mean that -cpu westmere and -M
>>> pc-1.1 will not work.
>>>
>>> This is where QEMU is going.  There is no reason that a normal user
>>> should ever use -nodefconfig.
>>
>> I don't think anyone or anything can use it, since it's meaning is not
>> well defined.  "not read any configuration files" where parts of qemu
>> are continually moved out to configuration files means its a moving
>> target.
>
> I think you assume that all QEMU users care about forward and
> backwards compatibility on the command line about all else.
>
> That's really not true.  The libvirt folks have stated repeatedly that
> command line backwards compatibility is not critical to them.  They
> are happy to require that a new version of QEMU requires a new version
> of libvirt.

I don't think this came out of happiness, but despair.  Seriously,
keeping compatibility is one of the things we work hardest to achieve,
and we can't manage it for our command line?

>
> I'm not saying that backwards compat isn't important--it is.  But
> there are users who are happy to live on the bleeding edge.

That's fine, but I don't see how -nodefconfig helps them.  All it does
is take away the building blocks (definitions) that they can use when
setting up their configuration.

>
>> Suppose we define the southbridge via a configuration file.  Does that
>> mean we don't load it any more?
>
> Yes.  If I want the leanest and meanest version of QEMU that will
> start in the smallest number of milliseconds, then being able to tell
> QEMU not to load configuration files and create a very specific
> machine is a Good Thing.  Why exclude users from being able to do this?

So is this the point?  Reducing startup time?

I can't say I see the reason to invest so much effort in shaving a
millisecond or less from this, but if we did want to, the way would be
lazy loading of the configuration where items are parsed as they are
referenced.

-- 
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