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[Xen-devel] Network freezing for paravirt linux, 3.0.3

To: xen-devel@xxxxxxxxxxxxxxxxxxx, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Network freezing for paravirt linux, 3.0.3
From: Andres Lagar Cavilla <andreslc@xxxxxxxxxxxxxx>
Date: Tue, 28 Nov 2006 10:08:11 -0500
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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


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