Re: PCI passthrough issue

[Jean Baptiste Favre <xen-devel@jbfavre.org>]

Hello,
My dom0 is back and I performed some more tests.

I told in my first mail that ping works. Indeed it works, but not always:
# ping -c2 10.0.0.1
PING 10.0.0.1 (10.0.0.1): 56 data bytes
64 bytes from 10.0.0.1: seq=0 ttl=64 time=0.846 ms
64 bytes from 10.0.0.1: seq=1 ttl=64 time=0.824 ms

--- 10.0.0.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.824/0.835/0.846 ms
# ping -c2 -s60 10.0.0.1
PING 10.0.0.1 (10.0.0.1): 60 data bytes
68 bytes from 10.0.0.1: seq=0 ttl=64 time=0.819 ms
68 bytes from 10.0.0.1: seq=1 ttl=64 time=0.807 ms

--- 10.0.0.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.807/0.813/0.819 ms

Increasing packet size is ok until this one:
# ping -c2 -s85 10.0.0.1
PING 10.0.0.1 (10.0.0.1): 85 data bytes
93 bytes from 10.0.0.1: seq=0 ttl=64 time=0.823 ms
93 bytes from 10.0.0.1: seq=1 ttl=64 time=0.816 ms

--- 10.0.0.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.816/0.819/0.823 ms
root@OpenWrt:/# ping -c2 -s86 10.0.0.1
PING 10.0.0.1 (10.0.0.1): 86 data bytes

--- 10.0.0.1 ping statistics ---
2 packets transmitted, 0 packets received, 100% packet loss

As you see, packet size seems to be limited in a way. From another
machine on the same LAN I can do ping -s1500 without any problem.

So I think I hit a bug. Either it's Xen related, or Debian (through
debian kernel version). Now the question is: how can I determine which
part is responsible ?

Regards,
JB


Le 13/01/2011 12:28, Jean Baptiste Favre a écrit :
> Have had a look on both tcpdump captures.
> 1. From the OpenWRT domU: nothing special. Lot of STP traffic due to my
> network architecture. Don't thing this could be the cause of my problem
> since I'm always able to reproduce the failure whatever could be the
> order of DNS requests. Don't see "big" DNS answers coming in, see
> multiple requests before timeout.
> 
> 2. From my gateway: nothing special here too. Same STP traffic (have
> checked GW network setup as well). See each DNS requests my domU sent
> and can see as well answers, which are not received by domU. No strange
> ARP traffic.
> 
> I wanted to change the network, thinking about a bogus driver (never
> know). My Dom0 has crashed during reboot and I've no way to remotely
> reboot it (no remote power control and it seems that Magic SysRQ are not
> transfered through my Putty/screen connection).
> 
> Will reboot it when at home and continue investigation with another
> network card and maybe another operating system to check if bad
> behaviour is still there.
> 
> Regards,
> JB