[Xen-users] Very slow domU network performance
I set up a domU as a backup server, but it has very, very poor
network performance with external computers. I ran some tests with
iperf and found some very weird results.
Using iperf, I get these approximate numbers (the left column is the
iperf client and the right column is the iperf server):
domU --> domU 1.77 Gbits/sec (using 127.0.0.1)
domU --> domU 1.85 Gbits/sec (using domU eth0 IP address)
dom0 --> domU 91.5 Mbits/sec
domU --> dom0 85.2 Mbits/sec
So far, so good. The relatively slow dom0<->domU communication may
indicate a problem, but it's fine for my purposes. The real problem
is when I use my iBook (running Mac OS X) to run some iperf tests.
The computers are connected via a crossover cable. They were
originally connected with a hub, but I changed to a crossover cable
connection to reduce variables (it turns out this had no effect).
dom0 --> iBook 89.0 Mbits/sec
iBook --> dom0 86.9 Mbits/sec
domU --> iBook 87.1 Mbits/sec
iBook --> domU 1.87 Mbits/sec
The last entry has me baffled. Why would it be so incredibly slow in
one direction but not the other?
I decided to run some UDP tests as well.
server: iperf -s -u -i 1
client: iperf -c server_ip -u -b 90M -t 5
The packet loss is as follows:
domU --> domU 0% (using 127.0.0.1)
domU --> domU 0% (using domU eth0 IP address)
dom0 --> domU ~100% (only 7 of 38464 made it!)
domU --> dom0 0.09%
dom0 --> iBook 4.7%
iBook --> dom0 0.33%
domU --> iBook 11%
iBook --> domU 1.6%
There are some odd things here. First, dom0->domU with UDP loses
almost everything, but the reverse direction is fine. Somehow, dom0-
>domU TCP was OK (if you consider ~90Mbps OK).
The second weird thing is that in contrast with TCP, UDP works fine
in both directions between the iBook and domU. There's 11% packet
loss in one case, but that's not a lot -- it's probably just a little
more than poor little iBook can handle.
My dom0 is Fedora Core 5, with the included xen0 kernel. The domU is
a very basic install of Centos 4.3, based on a jailtime.org image,
running the xensource 220.127.116.11-xenU kernel. The domU has bridged
networking and 64MB of RAM (I ran the iBook->domU TCP test with 196MB
of RAM but it was still ~2Mb/s). Firewalling is off in domU and
dom0; the only iptables rules are the ones created by the xen
Has anyone else seen anything like this, or have any idea what's
going on? This seems bizarre to me.
Thanks for any help.
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