Re: [Xen-devel] network hang trigger

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

Do you see this if you ping from DOM1 to an external machine? Or from
an external machine to DOM1?

My suspicion is that this is just some weird interaction between
bridging and local packet dleivery in DOM0. I also can cause lots of
packet loss when pinging DOM1 from DOM0, if I use DOM1's hostname
rather than IP address(!!!). It's very bizarre, and tcpdump tells me
that the ICMP packets come back to DOM0 via the VIF, but it looks like
they then get swallowed somehow within the bridge.

I think that the bridging code is really intended for dedicated bridge
boxes with no local IP interface. So I'm not sure whether the support
for that might not be flaky in some circumstances.

 -- Keir

> 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?


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