Strange network behaviour

Mike
2007-12-04T22:44:41Z

Hello,
I already spoke to Izik Eidus. He told me to publish the results to the
problem at the mailinglist.

Some time ago I wrote to the kvm-devel mailinglist that I had a problem
with my guests' networking dying.
I got the hint to change the network card emulation. That worked.

Now I noticed a strange behaviour.
I have a gameserver running in a guest os. No problems on performance
side, really fast.
The only thing, when I make a ping test after unspecific time periods I
get this: (this peaks are even there if the gameserver isn't running)

Reply from 195.24.77.170: bytes=32 time=36ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=123ms TTL=57
Reply from 195.24.77.170: bytes=32 time=98ms TTL=57
Reply from 195.24.77.170: bytes=32 time=116ms TTL=57
Reply from 195.24.77.170: bytes=32 time=241ms TTL=57
Reply from 195.24.77.170: bytes=32 time=72ms TTL=57
Reply from 195.24.77.170: bytes=32 time=382ms TTL=57
Reply from 195.24.77.170: bytes=32 time=135ms TTL=57
Reply from 195.24.77.170: bytes=32 time=397ms TTL=57
Reply from 195.24.77.170: bytes=32 time=647ms TTL=57
Reply from 195.24.77.170: bytes=32 time=857ms TTL=57
Reply from 195.24.77.170: bytes=32 time=1156ms TTL=57
Reply from 195.24.77.170: bytes=32 time=692ms TTL=57
Reply from 195.24.77.170: bytes=32 time=604ms TTL=57
Reply from 195.24.77.170: bytes=32 time=35ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=35ms TTL=57
Reply from 195.24.77.170: bytes=32 time=188ms TTL=57
Reply from 195.24.77.170: bytes=32 time=39ms TTL=57
Reply from 195.24.77.170: bytes=32 time=46ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=39ms TTL=57

This ping peaks are on *all* guests I'm currently running.
I did a ping test the same time to the Host, with this result:

Reply from 195.24.77.169: bytes=32 time=38ms TTL=57
Reply from 195.24.77.169: bytes=32 time=34ms TTL=57
Reply from 195.24.77.169: bytes=32 time=39ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57
Reply from 195.24.77.169: bytes=32 time=38ms TTL=57
Reply from 195.24.77.169: bytes=32 time=34ms TTL=57
Reply from 195.24.77.169: bytes=32 time=34ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57
Reply from 195.24.77.169: bytes=32 time=35ms TTL=57
Reply from 195.24.77.169: bytes=32 time=40ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57
Reply from 195.24.77.169: bytes=32 time=34ms TTL=57
Reply from 195.24.77.169: bytes=32 time=35ms TTL=57
Reply from 195.24.77.169: bytes=32 time=34ms TTL=57
Reply from 195.24.77.169: bytes=32 time=35ms TTL=57
Reply from 195.24.77.169: bytes=32 time=37ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57
Reply from 195.24.77.169: bytes=32 time=35ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57
Reply from 195.24.77.169: bytes=32 time=34ms TTL=57
Reply from 195.24.77.169: bytes=32 time=34ms TTL=57
Reply from 195.24.77.169: bytes=32 time=33ms TTL=57

As you can see, no peaks.
Example of start command from a guest:
kvm -hda apache.img -hdb apache_storage.img -m 512 -boot c -net
nic,vlan=0,macaddr=00:16:3e:00:00:01,model=rtl8139 -net tap -nographic
-daemonize

Here the pings from the guest started with the command line listed above:

Reply from 195.24.77.171: bytes=32 time=37ms TTL=57
Reply from 195.24.77.171: bytes=32 time=37ms TTL=57
Reply from 195.24.77.171: bytes=32 time=97ms TTL=57
Reply from 195.24.77.171: bytes=32 time=60ms TTL=57
Reply from 195.24.77.171: bytes=32 time=186ms TTL=57
Reply from 195.24.77.171: bytes=32 time=363ms TTL=57
Reply from 195.24.77.171: bytes=32 time=368ms TTL=57
Reply from 195.24.77.171: bytes=32 time=972ms TTL=57
Reply from 195.24.77.171: bytes=32 time=673ms TTL=57
Reply from 195.24.77.171: bytes=32 time=1133ms TTL=57
Reply from 195.24.77.171: bytes=32 time=1198ms TTL=57
Reply from 195.24.77.171: bytes=32 time=1881ms TTL=57
Reply from 195.24.77.171: bytes=32 time=2341ms TTL=57
Reply from 195.24.77.171: bytes=32 time=2401ms TTL=57
Reply from 195.24.77.171: bytes=32 time=2006ms TTL=57
Reply from 195.24.77.171: bytes=32 time=2638ms TTL=57
Reply from 195.24.77.171: bytes=32 time=3590ms TTL=57
Reply from 195.24.77.171: bytes=32 time=383ms TTL=57
Reply from 195.24.77.171: bytes=32 time=35ms TTL=57
Reply from 195.24.77.171: bytes=32 time=35ms TTL=57
Reply from 195.24.77.171: bytes=32 time=34ms TTL=57
Reply from 195.24.77.171: bytes=32 time=35ms TTL=57
Reply from 195.24.77.171: bytes=32 time=34ms TTL=57

So I tried disabling kvm when starting a guest.
and here the guest *with* -no-kvm in the command line:

Reply from 195.24.77.170: bytes=32 time=35ms TTL=57
Reply from 195.24.77.170: bytes=32 time=36ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=35ms TTL=57
Reply from 195.24.77.170: bytes=32 time=36ms TTL=57
Reply from 195.24.77.170: bytes=32 time=37ms TTL=57
Reply from 195.24.77.170: bytes=32 time=33ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=38ms TTL=57
Reply from 195.24.77.170: bytes=32 time=33ms TTL=57
Reply from 195.24.77.170: bytes=32 time=35ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=35ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=37ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=33ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57
Reply from 195.24.77.170: bytes=32 time=34ms TTL=57

The other guest, without -no-kvm have the ping peaks. Also here, no ping
peaks from the host.
Server load is really really low at the moment of the tests.

Maybe you have an idea where this peaks are coming from?
I'm using KVM-55 on Ubuntu 7.10 server with Kernel Linux A050
2.6.22-14-server #1 SMP Sun Oct 14 22:09:15 GMT 2007 x86_64 GNU/Linux.
My CPU is an AMD Athlon 64 X2 5600+ (Dual Core) with 8GByte of RAM.

Greetings from Luxembourg.
Mike Weimichkirch