There is a conflit between libvirt 0.1.8 and the latest release 3.0.3 of Xen. With Xen 3.0.3 release, the virsh vcpuinfo command (or virDomainGetVcpus API) always returns the 0 as physical CPU used by any vCPU. Example: #: xm vcpu-list VM1 Name ID VCPUs CPU State Time(s) CPU Affinity VM1 4 0 0 -b- 50.3 0 VM1 4 1 0 -b- 17.3 any cpu VM1 4 2 1 -b- 34.2 1 VM1 4 3 1 -b- 21.8 any cpu #: virsh vcpuinfo VM1 VCPU: 0 CPU: 0 ... VCPU: 1 CPU: 0 ... VCPU: 2 CPU: 0 ... VCPU: 3 CPU: 0 The same libvirt release 0.1.8 used with an older release of Xen gives a correct result. I currently investigate the problem but perhaps anyone has an idea of the origin of this problem.