[kvm-ppc-devel] virtio network traffic issues

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Hi,
I analyzed the network traffic to get a feeling where our bug may be located.
I summarize some things I think I see in that data

Environment:
192.168.1.2 = nfs host
192.168.1.3 = ppc host
192.168.1.4 = ppc host 2nd network interface (not active, but bridged to tap)
192.168.1.10 = ppc vkvm guest - configured via dhcp (working)


time 0-25: host nfs and telnet
time ~25:   DHCP discover from kvm guest + offer answer from dhcp server
       after that there are arp requests for the nfs host which are answered correctly
       the guest starts to get a portmap response for nfs and mounts the nfs share
       Then the guest does some nfs getattr, statfs calls followed by some larger read calls (fragmented)
       The read calls are single packets while the reply (the data) is fragmented
       In the wireshark protocol we even see that it accesses 1st dev/console and then /sbin/init (this is where the reads go to)
       This continues to ld.1.so and other libs which are read via nfs (response looks good)
packet 350 is retransmitted as packet 356 - there is no visible error - so it must have been a ?timeout?
then we get more retransmissions of that request ( there are replies to these requests all the time - does the guest not "see them"?)
packet 365 is then a reply to a getattr call before

=> it looks as if after #353 no packet was actually received by the guest
   after that only timeouts retransmits and unanswered arp requests are seen

packet 368-385 have some kind of arp flood asking for 192.168.1.10 (the kvm guest) but there is no reply to that too
First these are direct arp requests then broadcasts - this looks (as described above) as if after packet 353 no packet is recieved by the guest

The rest is my telnet connection aborting the kvm guest and some host->nfs server traffic not interesting for us:

Summary:
=> from one not yet defined point our guest seems to receive absolutely nothing
=> when the guest is hanging it sends nfs requests which are seen externally, but it does not seem to get the respones
=> the arp requests for the guest are repeated - maybe we can add some very verbose debug in the guest virtio code and activate it when we see that it is already hanging
=> ideas:
  - maybe some buffer/memory runs out and so incoming packets won't be received anymore 
  - we break something in virtio / incoming interrupts (or maybe a lock) and from that point no receive is possible


I'll continue on that and keep you informed

-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization

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