[libvirt-users] regard limiting network bandwidth

hi  all i am a kvm , qemu  user newbie , i am  using libvirt and virsh to mange my KVM VMs , i want to  limit the network bandwidth of each VM , i come across libvirt  xml format option : <forward mode='nat' dev='eth0'/> <bandwidth> <inbound average='1000' peak='5000' burst='5120'/> <outbound average='128' peak='256' burst='256'/> </bandwidth>to limit the bandwidth of each vm , however i have a question how does these option applied limit on  kvm vm ?  through using of linux cgroub or its a qemu network bandwidth  limit functionality ?