[libvirt-users] domain CPU topology

Hi When I create a domain from xml file, the vcpu number point in <vcpu/>, I not point <cpu><topology> in xml file, when allocate more than 2 vpcus, some(windows) system can't use all vcpu. But I point <cpu><topology sockets='1' cores='num' threads='1'/></cpu>. num is <vcpu>'num'</vcpu>. then whindows can use all vcpus. I want to know when no ponit <cpu><topology> ,what default cpu topology. if point cpu topology, what rule guide cpu topology, I find VMware Workstation can point cpu num,and core of per cpu. all cores is cpu*core.