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



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.


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