[dpdk-dev] [Bug 418] failsafe/tap PMD drops first UDP packet

[bugzilla at dpdk.org]

https://bugs.dpdk.org/show_bug.cgi?id=418

            Bug ID: 418
           Summary: failsafe/tap PMD drops first UDP packet
           Product: DPDK
           Version: 20.02
          Hardware: x86
                OS: Linux
            Status: UNCONFIRMED
          Severity: major
          Priority: Normal
         Component: ethdev
          Assignee: dev at dpdk.org
          Reporter: stephen at networkplumber.org
  Target Milestone: ---

On Azure, the first UDP packet of a flow is being dropped somewhere in the maze
of TAP PMD and Failsafe PMD.  The packet arrives into the kernel device
(netvsc) and is visible with tcpdump but is lost after that. Subsequent UDP
packets get redirected to VF and have no problem.

This is a TAP/Failsafe PMD problem, and not generic to DPDK. 
The Netvsc PMD does not have this problem.
The suggested fix is to use netvsc PMD instead..

To reproduce:

    Setup two 8 core VMs, with accelerated networking, running Ubuntu 18.

    On machine 1 run testpmd in rx only mode. My command line was:
 # testpmd -l 4,5 -w 0002:00:02.0 --vdev="net_vdev_netvsc0,iface=eth1" --
--forward-mode=rxonly --stats-period=1

    On machine 2 run netcat in UDP client mode.
      $ nc -u 192.168.100.12 1234

Type on machine 2. The first line (packet) is lost and stat does not increment.
Second line (packet) does show up.

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