[DPDK/ethdev Bug 1591] MLX5 Windows : Issue with Packet Loss When Setting Descriptors Above 1<<14 on ConnectX6-DX

[DPDK/ethdev Bug 1591] MLX5 Windows : Issue with Packet Loss When Setting Descriptors Above 1<<14 on ConnectX6-DX

[bugzilla]

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https://bugs.dpdk.org/show_bug.cgi?id=1591

            Bug ID: 1591
           Summary: MLX5 Windows : Issue with Packet Loss When Setting
                    Descriptors Above 1<<14 on ConnectX6-DX
           Product: DPDK
           Version: 24.11
          Hardware: x86
                OS: Windows
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: ethdev
          Assignee: dev@dpdk.org
          Reporter: a.pollenus@deltacast.tv
  Target Milestone: ---

I am encountering an issue with the ConnectX6-DX on Windows. When I set the
number of descriptors to a value greater than 1<<14, all my packets are dropped
(imissed), except for the first one. The root cause is unclear, but I observed
that the maximum number of descriptors reported by rte_eth_dev_info_get() is
32768 (rx_desc_lim.nb_max), which I believe indicates that the number of
descriptors should be set to this value or lower.

Here are some test results using testpmd that demonstrate the issue:

TEST 1 : 4096 descriptors

./dpdk-testpmd -l 2-3 -n 4 -a 0000:03:00.0 --log-level=8
--log-level=pmd.common.mlx5:8 --log-level=pmd.net.mlx5:8 -- --socket-num=0
--burst=64 --txd=4096 --rxd=4096 --mbcache=512 --rxq=4 --txq=4 --nb-cores=1
--txpkts=1500 -i --forward-mode=rxonly --flow-isolate-all

testpmd> show port stats 0

  ######################## NIC statistics for port 0  ########################
  RX-packets: 1626632    RX-missed: 0          RX-bytes:  2152490218
  RX-errors: 0
  RX-nombuf:  0
  TX-packets: 0          TX-errors: 0          TX-bytes:  0

  Throughput (since last show)
  Rx-pps:       246876          Rx-bps:   2613496560
  Tx-pps:            0          Tx-bps:            0
  ############################################################################


TEST 2 : 16384 descriptors
./dpdk-testpmd -l 2-3 -n 4 -a 0000:03:00.0 --log-level=8
--log-level=pmd.common.mlx5:8 --log-level=pmd.net.mlx5:8 -- --socket-num=0
--burst=64 --txd=4096 --rxd=16384 --mbcache=512 --rxq=4 --txq=4 --nb-cores=1
--txpkts=1500 -i --forward-mode=rxonly --flow-isolate-all
testpmd> show port stats 0

  ######################## NIC statistics for port 0  ########################
  RX-packets: 2923021    RX-missed: 0          RX-bytes:  3867975188
  RX-errors: 0
  RX-nombuf:  0
  TX-packets: 0          TX-errors: 0          TX-bytes:  0

  Throughput (since last show)
  Rx-pps:       246881          Rx-bps:   2613540240
  Tx-pps:            0          Tx-bps:            0
  ############################################################################

TEST 3 : 20480 descriptors
./dpdk-testpmd -l 2-3 -n 4 -a 0000:03:00.0 --log-level=8
--log-level=pmd.common.mlx5:8 --log-level=pmd.net.mlx5:8 -- --socket-num=0
--burst=64 --txd=4096 --rxd=20480 --mbcache=512 --rxq=4 --txq=4 --nb-cores=1
--txpkts=1500 -i --forward-mode=rxonly --flow-isolate-all

testpmd> show port stats 0

  ######################## NIC statistics for port 0  ########################
  RX-packets: 1          RX-missed: 2732098    RX-bytes:  1328
  RX-errors: 0
  RX-nombuf:  0
  TX-packets: 0          TX-errors: 0          TX-bytes:  0

  Throughput (since last show)
  Rx-pps:            0          Rx-bps:            0
  Tx-pps:            0          Tx-bps:            0
  ############################################################################

TEST 4 : 32768 descriptors

./dpdk-testpmd -l 2-3 -n 4 -a 0000:03:00.0 --log-level=8
--log-level=pmd.common.mlx5:8 --log-level=pmd.net.mlx5:8 -- --socket-num=0
--burst=64 --txd=4096 --rxd=32768 --mbcache=512 --rxq=4 --txq=4 --nb-cores=1
--txpkts=1500 -i --forward-mode=rxonly --flow-isolate-all
testpmd> show port stats 0

  ######################## NIC statistics for port 0  ########################
  RX-packets: 1          RX-missed: 1129806    RX-bytes:  1328
  RX-errors: 0
  RX-nombuf:  0
  TX-packets: 0          TX-errors: 0          TX-bytes:  0

  Throughput (since last show)
  Rx-pps:            0          Rx-bps:            0
  Tx-pps:            0          Tx-bps:            0
  ############################################################################


I was able to reproduce this issue on versions 24.11 and 23.11, using DevX
version 24.10.26603.

Thank you in advance for your help,

Please let me know if you need further information.

Thank you.

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