Network freezing for paravirt linux, 3.0.3

[Andres Lagar Cavilla <andreslc@cs.toronto.edu>]

Hi,
as part of My Xen-GL work I've been experiencing some temporary domU 
network outages.

At a very basic level I'm using the TCP/IP stack to transport OpenGL 
command from the domU to dom0, where they can be directly executed on 
some nice piece of graphics hardware. Now, beasts like Enemy Territory 
or Unreal Tournament 2004 seem to exceed a gigabit of bandwidth 
utilization. All those bots and rich textures don't help much :)

At points in the game domU networking completely freezes, becoming 
unresponsive to ssh, ping, the openGL transport, and other services I 
tried. Other simptoms:
    - Tcpdump reveals that the only traffic on the vifX.Y are inbound 
broadcasts.
    - There are no dropped packets (as shown by ifconfig and 
/proc/net/dev).
    - Happens with both transmit checksumming offload enabled and disabled.
    - Measured from both dom0 and domU.
    - Both with network bridging and routing.
    - Did not happen for an hvm doing network emulation (did happen for 
PV-on-HVM network driver).
    - For whatever it's worth, doesn't happen with vmware network 
emulation either.

It thus looks like the culprit is netfront, or possibly a 
netback/netfront interaction (Q: is netback employed in the qemu-dm 
emulation path, or packets are simply relayed from the tap to vifX.Y?).
I would love to provide more information, but I'm unsure where to get it.

Andres