Guest OS drapping packets with RedHat loopback example and 65535 byte packets

["Nicolson Ken (ニコルソン ケン)" <ken.nicolson@jp.panasonic.com>]

Hi all,

Using DPDK 22.11.2 on CentOS

I've configured my Guest OS according to the RedHat tutorial here:

https://www.redhat.com/en/blog/hands-vhost-user-warm-welcome-dpdk

Using the commandline:

root@guest $ testpmd -l 0,1,2 --socket-mem 1024 -n 4 \
    --proc-type auto --file-prefix pg -- \
    --portmask=3 --forward-mode=macswap --port-topology=chained \
    --disable-rss -i --rxq=1 --txq=1 \
    --rxd=256 --txd=256 --nb-cores=2 --auto-start

In my host, I have my own code that sends fixed-size mbufs; if I use 9000 byte packets (ie 5 mbufs in a chain) with a speed of 15Gbps (ie about 200,000 packets per second), everything runs smoothly, but if I go up to 65535 byte packets (32 mbufs in a chain) at 15Gbps (almost 29,000 packets per second) I start losing packets. A burst of 100 packets, for instance, will see all 100 received, but only 7 forwarded.

If I use the following with the same 100 packet burst:

testpmd> set verbose 3

I see 14 pairs of Rx and Tx packets.

testpmd> set verbose 2

Gives 18 Rx packets and 14 Tx. "show port stats all" shows no Rx or Tx errors, either in Guest or Host.

There's something very weird going on, but I haven't a clue where to start looking!

Has anyone got any hints for me for where to look or to get more debug info? Common sense would suggest that larger 

Thanks,
Ken