Re: strange guest slowness after some time

[Tomasz Chmielewski <mangoo@wpkg.org>]

Felix Leimbach schrieb:

>> OK, another bug found.
>>
>> Set your MTU to 100.
>>
>> On two hosts, do:
>>
>> HOST1_MTU1500# dd if=/dev/zero | ssh manager@HOST2 dd of=/dev/null
>> HOST2_MTU100# dd if=/dev/zero | ssh manager@HOST1 dd of=/dev/null
>>
>> HOST2 with MTU 100 will crash after 10-15 minutes (with packet count 
>> still not overflown).
>>
> Intersting. What are the packet counter at crash time (roughly)?
> 
> My - currently running - test is:
> 
> Guest 1 (Linux):
> MTU 150
> # cat /dev/zero | nc <guest2ip> 7777
> 
> Guest 2 (Windows 2003 Server):
> MTU: 1500
> # nc -l -p 7777 > NUL
> 
> My packet are currently at 63 million without a problem - yet.

I have it running with MTU 1500. And one of the guests (the one which 
was crashing with MTU=100) froze.

On a VNC console I can see:

virtio_net virtio0: id 64 is not a head!
BUG: soft lockup - CPU#0 stuck for 61s! [ssh:2265]

And "soft lockup" is being printed periodically. VNC and serial console 
do not react to any key press. Guest do not react on ACPI events (shutdown).
kvm/qemu process is using 100% CPU.

See this screenshot:

http://www1.wpkg.org/lockup.png


Guest that locks up is running Debian Lenny with 2.6.26 kernel.
Guest that does not lock up runs Mandriva 2009.0 with 2.6.27.x kernel.
(data being transferred both side to/from each of these hosts).



-- 
Tomasz Chmielewski
http://wpkg.org