[dpdk-dev] [Bug 96] mlx5: TX error for multi-seg packet where first segment has 14~18 bytes

[dpdk-dev] [Bug 96] mlx5: TX error for multi-seg packet where first segment has 14~18 bytes

[bugzilla]

https://bugs.dpdk.org/show_bug.cgi?id=96

            Bug ID: 96
           Summary: mlx5: TX error for multi-seg packet where first
                    segment has 14~18 bytes
           Product: DPDK
           Version: 18.08
          Hardware: x86
                OS: Linux
            Status: CONFIRMED
          Severity: normal
          Priority: Normal
         Component: ethdev
          Assignee: dev@dpdk.org
          Reporter: sunnylandh@gmail.com
  Target Milestone: ---

Created attachment 14
  --> https://bugs.dpdk.org/attachment.cgi?id=14&action=edit
program to reproduce bug

mlx5 driver fails to transmit a 2-segment packet where the first segment has
14, 15, 16, or 17 bytes.
mlx5 driver reports "mlx5_tx_complete(): unexpected error CQE, Tx stopped"
error when transmitting a 2-segment packet where the first segment has 18
bytes.

Steps to Reproduce:

1) Use a fiber to connect two ConnectX-5 or ConnectX-4 Ethernet adapters
together.
2) Run `ip link set NETDEV mtu 9000` to increase MTU.
3) Run tcpdump to observe traffic on the second Ethernet adapter.
4) Execute the attached tx-firstseg18.c program on the first Ethernet adapter.



Actual Results:

1) tcpdump does not receive any packets.
2) The program reports "mlx5_tx_complete(): unexpected error CQE, Tx stopped".

Expected Results:

1) tcpdump receives packets.

Build Date & Hardware:

1) Ubuntu 18.04 Server, with gcc 7.3.0
2) DPDK 18.08, with the following config:
   CONFIG_RTE_LIBRTE_MLX5_PMD=y
   CONFIG_RTE_LIBRTE_MLX5_DEBUG=y
   CONFIG_RTE_LIBRTE_MBUF_DEBUG=y
3) Mellanox Technologies MT27800 Family [ConnectX-5]
   Mellanox Technologies MT27700 Family [ConnectX-4]

Additional Information:

In the attached tx-firstseg18.c program, there's a line "#define
SIZE_OF_FIRST_SEG (sizeof(ethhdr) + 4)". Changing the number "4" to 0, 1, 2, or
3 makes the "mlx5_tx_complete(): unexpected error CQE, Tx stopped" error
disappear, but tcpdump still does not receive packets. Changing the number "4"
to 5 or greater causes everything to work, i.e. no error and tcpdump receives
packets.

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