Re: [Qemu-devel] cpuid problem in upstream qemu with kvm

[Anthony Liguori <anthony@codemonkey.ws>]

On 01/06/2010 08:48 AM, Dor Laor wrote:
> On 01/06/2010 04:32 PM, Avi Kivity wrote:
>> On 01/06/2010 04:22 PM, Michael S. Tsirkin wrote:
>>>> We can probably default -enable-kvm to -cpu host, as long as we 
>>>> explain
>>>> very carefully that if users wish to preserve cpu features across
>>>> upgrades, they can't depend on the default.
>>> Hardware upgrades or software upgrades?
>>
>> Yes.
>>
>
> I just want to remind all the the main motivation for using -cpu 
> realModelThatWasOnceShiped is to provide correct cpu emulation for the 
> guest. Using a random qemu|kvm64+flag1-flag2 might really cause 
> trouble for the guest OS or guest apps.
>
> On top of -cpu nehalem we can always add fancy features like x2apic, etc.

I think it boils down to, how are people going to use this.

For individuals, code names like Nehalem are too obscure.  From my own 
personal experience, even power users often have no clue whether there 
processor is a Nehalem or not.

For management tools, Nehalem is a somewhat imprecise target because it 
covers a wide range of potential processors.  In general, I think what 
we really need to do is simplify the process of going from, here's the 
output of /proc/cpuinfo for a 100 nodes, what do I need to pass to qemu 
so that migration always works for these systems.

I don't think -cpu nehalem really helps with that problem.  -cpu none 
helps a bit, but I hope we can find something nicer.

Regards,

Anthony Liguori