[libvirt-users] how virt-manager gets CPU usage of Guest

Hi, Does anybody know how virt-manager is getting the CPU usage of the guests? I need to know how to get the CPU usage of the guests and this is the only way I can think of. In other words, how does virt-manager produce the graph of the CPU usage of EACH guest in KVM? I don't actually need the graph, I just need to get the percentage(%) since I'm trying to create a Java program to get the CPU usage of each guest in KVM. Thanks! regards, Marco