Re: strange guest slowness after some time

[Avi Kivity <avi@redhat.com>]

Tomasz Chmielewski wrote:
> 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).

Copying the virtio folks... something is wrong.

You can obtain a stack trace of the locked up guest by doing

  (qemu) gdbserver 1234

  $ gdb /path/to/guest/vmlinux
  (gdb) target remote localhost:1234
  (gdb) backtrace

I don't know host you obtain the guest vmlinux on debian; on Fedora it 
is contained in kernel-debuginfo.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.