When Windows installed selects the HAL library appropriate the the hardware. If you install on a single CPU system then the uniprocessor HAL is installed.
If you then add a second vcpu to the guest then the windows HAL won't see it.
You'll need to replace Window's hal. See links below for some background. I don't think there is a Microsoft *supported* way to do this but I've done this a number of times without issue on XP and 2000, but I've not tried this on 2003, 2008 or Vista

http://support.microsoft.com/kb/309283/en-us
http://support.microsoft.com/default.aspx?scid=kb;EN-US;237556



On Sat, 2008-04-19 at 10:40 -0700, David Levinger wrote:
Hey Guys,

I have a fully virtualized XP guest that is set to have 2 VCPUs and in the guest I see 2 CPUs but when it is under heavy load it only utilizes 1 of the physical cores.

Both xm and virsh show that the guest only has 1 CPU, but my config file and the guest show it should have 2.

What am I missing? How can I get this guest to have access to both cores?

Thanks!

David

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