virtio net adapter driver with kvm slow on winxp

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 12.04.1 LTS
Release:        12.04
Codename:       precise

#virsh version 
Compiled against library: libvirt 1.0.4
Using library: libvirt 1.0.4
Using API: QEMU 1.0.4
Running hypervisor: QEMU 1.2.0

windows xp clean install with spice-guest-tools-0.52.exe from
  http://spice-space.org/download/windows/spice-guest-tools/spice-guest-tools-0.52.exe

it comes very slow , and the Interrupts process got very high cpu usage(above 60%).
when i switch the net adapter from virtio to default(rtl8139) ,it works well.