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apport-collect 1940928

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This change has been made by an automated script, maintained by the
Ubuntu Kernel Team.

** Changed in: linux (Ubuntu)
       Status: New => Incomplete

** Tags added: focal

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https://bugs.launchpad.net/bugs/1940928

Title:
  Inconsistent behavior in NIC RSS queue loading

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Utilizing kvms with ubuntu we face this inconsistent issue where an
  instance only uses a single rx queue (4 vCPUs):

  ethtool -S ens7 | egrep 'rx-.\.|rx_discards: '
  rx_discards: 0
  rx-0.packets: 2653705823
  rx-0.bytes: 561319217396
  rx-1.packets: 0
  rx-1.bytes: 0
  rx-2.packets: 0
  rx-2.bytes: 0
  rx-3.packets: 0
  rx-3.bytes: 0

  building another identical instances however sometimes works on all 4
  (4 vCPUs):

  ethtool -S ens6 | egrep 'rx-.\.|rx_discards: '
  rx_discards: 0
  rx-0.packets: 234661700
  rx-0.bytes: 49678565503
  rx-1.packets: 231886603
  rx-1.bytes: 49022714157
  rx-2.packets: 232424910
  rx-2.bytes: 49313057910
  rx-3.packets: 235776722
  rx-3.bytes: 49863841179

  Applying the following workaround to the non-working instance:

  ethtool -L ens7 combined 2
  ethtool -L ens7 combined 4

  makes all RSS queues work properly (4). This looks like a race
  condition during boot or a kernel bug.

  The kernel used during the tests is:
  5.4.0-81-generic #91-Ubuntu SMP Thu Jul 15 19:09:17 UTC 2021 x86_64 x86_64 
x86_64 GNU/Linux

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