Re: network hang trigger

[Chris Andrews <chris@nodnol.org>]

I'm seeing this problem:

81.187.70.17 is a secondary on DOM0's bridge. The host 'uml18' is DOM1.

uml18:~# ping -s 2473 81.187.70.17
PING 81.187.70.17 (81.187.70.17) 2473(2501) bytes of data.
2481 bytes from 81.187.70.17: icmp_seq=1 ttl=64 time=0.559 ms

.. time passes, I hit ^C ..

ping: sendmsg: No buffer space available
ping: sendmsg: No buffer space available
ping: sendmsg: No buffer space available
ping: sendmsg: No buffer space available
ping: sendmsg: No buffer space available
ping: sendmsg: No buffer space available
2481 bytes from 81.187.70.17: icmp_seq=6 ttl=64 time=30297 ms
--- 81.187.70.17 ping statistics ---
12 packets transmitted, 2 received, 83% packet loss, time 34627ms
rtt min/avg/max/mdev = 0.559/15149.215/30297.872/15148.657 ms, pipe 7

DOM0 has 384M, DOM1 has 64M, MTU 1500 in both.

Different packet sizes seem to trigger the bug more or less quickly -- I 
first tried with 2000 byte packets, and didn't see the problem, then I tried 
2473, and saw the problem then. Trying 2000 bytes again did then show the 
problem.

This is running Xen-2.0 from 4th September -- I can give a more recent 
version a try, but should I be able to turn on writable pagetables with 
current code, given I had problems with that option with the code I'm 
running now?

Chris.


Keir Fraser wrote:
> I can't reproduce this. e.g.,
>  [root@druid-0 root]# ping -s 2473 128.232.39.40
>  PING 128.232.39.40 (128.232.39.40) 2473(2501) bytes of data.
>  2481 bytes from 128.232.39.40: icmp_seq=0 ttl=64 time=0.074 ms
>  2481 bytes from 128.232.39.40: icmp_seq=1 ttl=64 time=0.057 ms
>  2481 bytes from 128.232.39.40: icmp_seq=2 ttl=64 time=0.055 ms
>  2481 bytes from 128.232.39.40: icmp_seq=3 ttl=64 time=0.057 ms
> 
> Both domains have 256MB memory. MTU for both is 1500.
> 
>  -- Keir
> 
> 
>>I have found that simply doing a ping with packetsize > 1500 (maybe
>>mtu???) causes the network to hang for a short time. This is from xenU
>>and xen0 on the same machine.
>>
>>Can someone else _please_ test this? I am able to make the network hang
>>by saying from domU:
>>ping -s 1473 <dom0 ip>
>>(1473 + 28 byte header = 1501 byte packet)
>>
>>I'll do more testing tomorrow.
>>
>>thanks
>>
>>James
>>
>>
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> I have found that simply doing a ping with packetsize > 1500 (maybe
> mtu???) causes the network to hang for a short time. This is from xenU
> and xen0 on the same machine.
> 
> Can someone else _please_ test this? I am able to make the network hang
> by saying from domU:
> ping -s 1473 <dom0 ip>
> (1473 + 28 byte header =3D 1501 byte packet)
> 
> I'll do more testing tomorrow.
> 
> thanks
> 
> James
> 
> 
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