[CentOS-virt] How does KVM handle multiple cores?

[MargoAndTodd]

Hi All,

How does KVM handle multiple cores.  I have an x5650 with 6 real cores
that presents itself to my OS as 12 virtual cores (hyperthreading).

Does KVM see 6 or 12 cores.

And, can I tell KVM how many cores I want it to use?

Am I misunderstanding how KVM works?

What I am after is if my guest is 100% busy, I still
want some power left over for my host.

Many thanks,
-T