ros kvm optimization

Hi, in the nearest future i’m planning to go for a x86 ros platform and i want to know how efficient is the kvm virtualization used in ros since i preffer to use this feature instead of buying another separate platform for my linux needs. Also is there any option to set nr of cores to be used by the vm? The vm can be any os? windows/linux/unix

http://wiki.mikrotik.com/wiki/Kvm

I am not sure about the linux and unix but its work best in Windows http://www.linux-kvm.org/page/FAQ#Does_KVM_support_SMP_hosts.3F