[libvirt] Can not get domain's cpu time

Hi, I have a domain running in my KVM box, and try to get its vcpu info by calling virDomainGetVcpus(), but it seems the cpu time returned to me is always 0. And I also found virsh can not get the CPU time too: $ virsh vcpuinfo aaa VCPU: 0 CPU: 0 State: running CPU Affinity: yy I tried the same virsh command in my Xen box for a running domain, the output is: $ virsh vcpuinfo test1 VCPU: 0 CPU: 1 State: running CPU time: 322.1s <----- I need this CPU Affinity: yy As you see, for KVM domain, there is no "CPU time". But it's very strange that virt-manager can show the right CPU usage for my running domain, I do not know where virt-manger gets it. Can anyone tell me which libvirt API should I call to get the CPU time? Thanks! Regards, Qian