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  1. RHEL
  2. RHEL-7219

[Azure][RHEL-9] UDP data loss is big at packets larger than MTU even without vRSS hashing

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      +++ This bug was initially created as a clone of Bug #2128446 +++

      Description of problem:
      UDP data loss is supposed be less then 1% in the below situation.
      1. vRSS hashing excludes the port where UDP data is through.

      1. ethtool -n eth0 rx-flow-hash udp4
        UDP over IPV4 flows use these fields for computing Hash flow key:
        IP SA
        IP DA
        2. Packets length is larger than MTU, e.g. 8k.

      Tested with 2 Standard_D15_v2 VMs using the below commands on each respectively:

      1. iperf3 -s 4 -p 8001
      2. iperf3 -u -c 10.0.0.4 -p 8001 -4 -b 0 -l 8k -P 64 -t 60 --get-server-output -i 60

      And the result is:
      [ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
      [ 5] 0.00-60.01 sec 1.09 MBytes 152 Kbits/sec 4.741 ms 31221/31360 (1e+02%) receiver
      [ 6] 0.00-60.01 sec 944 KBytes 129 Kbits/sec 3.708 ms 30642/30760 (1e+02%) receiver
      ...
      [SUM] 0.00-60.01 sec 55.2 MBytes 7.71 Mbits/sec 5.510 ms 1646217/1653281 (1e+02%) receiver

      Version-Release number of selected component (if applicable):
      5.14.0-162.el9.x86_64

      How reproducible:
      100% on Azure.

      Steps to Reproduce:
      1. Create 2 VMs and disable vRSS hashing by -

      1. ethtool -N eth0 rx-flow-hash udp4 sd
        2. run iperf3 commands in description individually.

      Actual results:
      Data loss is greater than 1%.

      Expected results:
      Data loss is less than 1%.

      Additional info:
      1. This issue presents from 8.6 through 9.1.
      2. Related BZ - https://bugzilla.redhat.com/show_bug.cgi?id=1474300 (looks like a re-occurrence).
      3. Issue does not present when packets are smaller than MTU.
      4. Issue presents on other VM sizes, e.g. Standard_D16s_v5.

              mlevitsk Maxim Levitsky
              litian@redhat.com Li Tian
              Maxim Levitsky Maxim Levitsky
              Li Tian Li Tian
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                Created:
                Updated:
                Resolved: