Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models

[Andreas Färber]

Am 23.06.2015 um 18:38 schrieb Eduardo Habkost:
> On Tue, Jun 23, 2015 at 06:33:05PM +0200, Michael S. Tsirkin wrote:
>> On Tue, Jun 23, 2015 at 05:25:55PM +0100, Daniel P. Berrange wrote:
>>> Whether QEMU changed the CPU for existing machines, or only for new
>>> machines is actually not the core problem. Even if we only changed
>>> the CPU in new machines that would still be an unsatisfactory situation
>>> because we want to be able to be able to access different versions of
>>> the CPU without the machine type changing, and access different versions
>>> of the machine type, without the CPU changing. IOW it is the fact that the
>>> changes in CPU are tied to changes in machine type that is the core
>>> problem.
>>
>> But that's because we are fixing bugs.  If CPU X used to work on
>> hardware Y in machine type A and stopped in machine type B, this is
>> because we have determined that it's the right thing to do for the
>> guests and the users. We don't break stuff just for fun.
>> Why do you want to bring back the bugs we fixed?
> 
> I didn't take the time to count them, but I bet most of the commits I
> listed on my previous e-mail message are not bug fixes, but new
> features.

Huh? Of course the latest machine model get new features. The point is
that the previous ones don't and that's what we are providing them for -
libvirt is expected to choose one machine and the contract with QEMU is
that for that machine the CPU does *not* grow new features, and we're
going at great lengths to achieve that. So this thread feels more and
more weird...

Regards,
Andreas

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