[libvirt-users] a question on vCPU setting for lxc

Dear all, I am not clear about the 'vcpu' element for CPU allocation. I allocated 1 vCPU to my container, after I started the container, I ran 4 computation-intensive tasks on the container. And I found all the 4 physical core are 100% used (my host has 4 physical cores and no other application ran on the host except the container). That is, all available cores were used by the container. I want to know how to give a hard limitation for CPU usage of a container. So I don't understand what 'vcpu' setting can be used for. I know that another CPU allocation element 'shares' can also be used, but this elements only give a relative quota. If new containers are started, the CPU quota for the already started containers will change. Regards, Cheng