Allow Guests Access to Host CPU
In order to guarantee migration between physical hosts does not result in non-functioning virtual machines, QEMU & KVM disable the guest's ability to directly access some of the features which may be exclusive to the host CPU.
In the case where machine migration does not occur, ie. in machines 'assigned' to a particular node (due to hardware restrictions, etc.), this behavior can be bypassed, and may provide significant performance benefits.
- Change the Processor type to "CPU type: host" via the hardware tab
- Stop then start the VM (a reboot is not enough to initiate the change).
'CPU Performance' on the official KVM project website: http://www.linux-kvm.org/page/Tuning_KVM