[dpdk-dev] Issue with pktgen-dpdk replaying >1500bytes pcap on MCX4

[Damien Clabaut <damien.clabaut@corp.ovh.com>]

Hello DPDK devs,

I am sending this message here as I did not find a bugtracker on the 
website.

If this is the wrong place, I would kindly apologize and ask you to 
redirect me to the proper place,

Thank you.

Description of the issue:

I am using pktgen-dpdk to replay a pcap file containing exactly 1 packet.

The packet in question is generated using this Scapy command:

pkt=(Ether(src="ec:0d:9a:37:d1:ab",dst="7c:fe:90:31:0d:52")/Dot1Q(vlan=2)/IP(dst="192.168.0.254")/UDP(sport=1020,dport=1021)/Raw(RandBin(size=8500)))

The pcap is then replayed in pktgen-dpdk:

./app/app/x86_64-native-linuxapp-gcc/pktgen -l 0-7 -- -m [1-7].0 -s 
0:pcap/8500Bpp.pcap

When I run this on a machine with Mellanox ConnectX-4 NIC (MCX4), the 
switch towards which I generate traffic gets a strange behaviour

#sh int et29/1 | i rate
   5 seconds input rate 39.4 Gbps (98.4% with framing overhead), 0 
packets/sec

A capture of this traffic (I used a monitor session to redirect all to a 
different port, connected to a machine on which I ran tcpdump) gives me 
this:

19:04:50.210792 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 
(oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
19:04:50.210795 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 
(oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
19:04:50.210796 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 
(oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
19:04:50.210797 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 
(oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500
19:04:50.210799 00:00:00:00:00:00 (oui Ethernet) > 00:00:00:00:00:00 
(oui Ethernet) Null Unnumbered, ef, Flags [Poll], length 1500

The issue cannot be reproduced if any of the following conditions is met:

- Set the size in the Raw(RandBin()) to a value lower than 1500

- Send the packet from a Mellanox ConnectX-3 (MCX3) NIC (both machines 
are indentical in terms of software).

Is this a known problem ?

I remain available for any question you may have.

Regards,

-- 
Damien Clabaut
R&D vRouter
ovh.qc.ca