libvirt Qos

<devices>
    <interface type='network'>
      <source network='default'/>
      <target dev='vnet0'/>
      <bandwidth>
        <inbound average='1000' peak='5000' burst='1024'/>
        <outbound average='128' peak='256' burst='256'/>
      </bandwidth>
    </interface>
  <devices>

http://libvirt.org/formatdomain.html#elementsNICSTargetOverride

more example look for /etc/libvirt/nwfilter/