[libvirt] Is it possible to use more then 2 CPUs in the guest?

[Gerrit Slomma]

Daniel P. Berrange schrieb:
> On Thu, Aug 06, 2009 at 12:59:19PM +0100, Tom Hughes wrote:
>   
>> On 06/08/09 12:36, Daniel P. Berrange wrote:
>>     
>>> On Wed, Aug 05, 2009 at 10:11:07AM +0200, Mirko Raasch wrote:
>>>
>>>       
>>>> in my server i use an Intel Quad Core CPU and i want to use in one
>>>> WindowsXP guest all 4 cores.
>>>> The device manager shows four CPU (Qemu Virtual CPU version 0.10.5).
>>>> When i start prime95 or superpi, only 2 of them are in use. CPU-Z shows
>>>> also 2 Cores, instead of 4 like the device manager.
>>>>         
>>> I don't know what those apps are, but they sound broken to me. If the
>>> guest has been launched with 4 virtual CPus, the guest OS should be
>>> able to use them, regardless of what your host core/socket/thread cpu
>>> topology is. KVM/QEMU allow upto 16  virtual CPUs IIRC, and this is
>>> totally independant of how many physical CPUs you have.
>>>       
>> As other people have already said, it's a Windows licensing thing where 
>> some versions of Windows are designed to only work on a limited number 
>> of physical CPU packages. So they will run 4-way on a quad core but not 
>> on four single core CPUs.
>>     
>
> Oh I see what you mean, that really sucks horribly. There's no real 
> workaround for that kind of problem at this time I'm afraid, other
> than to not use that version of Windows ;-)
>
> Daniel
>   
"that version of Windows" in a productive virtualization environment 
could as well be a Windows 2k3 or 2k8 Standard or Enterprise Edition run 
on a dual socket Nehalem Server or a beefed out Dunnignton. 16 or 24 
Threads are available to the Host and could be passed on to the guest 
but 2k3 and 2k8 Standard only uses 4, Enterprise Edition 8 of the cores. 
Only the Datacenter-version is good for 32/64 sockets (32/64 bits 
respectively).

http://www.microsoft.com/germany/windowsserver2008/editionen/spezifikationen.mspx

By the way: Isn't this an issue for the licensing terms of Red Hat 
Enterprise Linux? There also applies a 2 socket constraint for the 
Server license, only on the Advanced Plattform you could use more sockets.

I could test what is detected by windows if i choose another cpu-model 
than "qemu" when invoking kvm.
Couldn't it made possible to choose the cpu-model via libvirt?

Another question (illposted here): How do i register KVM-Virtual 
Machines in RHN? The appear in RHN in the Virtualization-tab but can't 
be assigned to a channel, this only works for Xen-guests... Is there a 
point in the RHEL5.4 Documentation which describes this?

Gerrit.