Re: PCI passthrough issue

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jan 13, 2011 at 08:18:33PM +0100, Jean Baptiste Favre wrote:
> 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.

One thing that I just thought (which I keep on forgetting to do).
You did set 'iommu=soft' in your Linux guest, right?

> 
> 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 ?

What does tcpdump tell you when you try to send it at -s86?