Network performance regression with vde_switch

I've noticed a significant network performance regression when using vde_switch, starting about one week ago (10/05/2012); before that date, I used to get about 1.5 Gbits host to guest, but now I can only get about 320 Mbits; I didn't find any modification in net/vde.*, just in hw/virtio*.

My command line: 
 qemu-system-i386 -cdrom /bpd/bpd.iso -m 512 -boot d -enable-kvm \
  -localtime -ctrl-grab -usbdevice tablet \
  -device virtio-net-pci,mac=52:54:00:18:01:01,netdev=vde0,tx=bh,ioeventfd=on,x-txburst=32 \
  -netdev vde,id=vde0 -vga std -tb-size 2M -cpu host -clock unix

My host runs a kernel 3.6.1 and my guest runs a kernel 3.5.4; the same problem happens with other host and guest versions, too.

I know there are better ways of running a guest, but using vde I get a cleaner environment in the host (just one tun/tap interface to manage...), which is quite good when running some accademic experiments.

Interestingly, at the same time I've noticed a performance enhancement of about 25~30 % when using a tun/tap interface, bridged or not.

Thank you, very much.

Edivaldo de Araujo Pereira