iperf problem with Windows SMP VM

[ANNIE LI <annie.li@oracle.com>]

Hi

I am developing Window pv network driver and hit a problem now.

My server use Xen 3.1.4 and have 2 physical CPUs. When I create two VM 
with 1 VCPU on a same server, iperf performance is OK between those two 
VM, but there is performance degradation between those 2 VM when i 
increase VCPU from 1 to 2. 
This problem occurs in QEMU mode too.

Does Xen 3.1.4 has such problem or anything wrong in my configure file?

My configure file is as following:

acpi = 1
apic = 1
boot = 'c'
builder = 'hvm'
bootloader = '/usr/bin/pygrub'
device_model = '/usr/lib/xen/bin/qemu-dm'
disk = [
'file:/mnt/data/win2k3/Sys.img,hda,w!',
]
kernel = '/usr/lib/xen/boot/hvmloader'
memory = '600'
name = 'win2k3_s'
on_crash = ''
on_reboot = ''
serial = 'pty'
timer_mode = 1
usbdevice = 'tablet'
vcpus = 1
vif = [
'type=ioemu, mac=00:16:3E:55:D1:80, bridge=xenbr0',
]
vnc = 1
vncconsole = 1
vnclisten = '0.0.0.0'
vncpasswd = ''
vncunused = 1


Thanks
Annie.