Re: strange guest slowness after some time

[Tomasz Chmielewski <mangoo@wpkg.org>]

Tomasz Chmielewski schrieb:
> Avi Kivity schrieb:
>> Felix Leimbach wrote:
>>> Tomasz Chmielewski wrote:
>>>> Avi Kivity schrieb:
>>>>> Might it be that some counter overflowed?  What are the packet 
>>>>> counts on long running guests?
> 
>>> Here is the current ifconfig output of a machine which suffered the 
>>> problem before:
>>>
>>> eth0      Link encap:Ethernet  HWaddr 52:54:00:74:01:01
>>>          inet addr:10.75.13.1  Bcast:10.75.255.255  Mask:255.255.0.0
>>>          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>>          RX packets:3542104 errors:0 dropped:0 overruns:0 frame:0
>>>          TX packets:412546 errors:0 dropped:0 overruns:0 carrier:0
>>>          collisions:0 txqueuelen:1000
>>>          RX bytes:682285568 (650.6 MiB)  TX bytes:2907586796 (2.7 GiB)
>>
>> packet counters are will within 32-bit limits.  byte counters not so 
>> interesting.
> 
> Ah OK.
> I did only byte overflow.
> 
> Packet overflow will take much longer. It's one of these very rare cases 
> where setting very small MTU is useful...

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).


-- 
Tomasz Chmielewski
http://wpkg.org