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[sean mooney <smooney@xxxxxxxxxx>]

this goes back to when the feature was intoduced but this was reported
against a centos/rhel host on rocked and release before queens will be
out of support in a week or so, as such there is likely no point in
going back further then queens. i don't think this issue will be present
on other distros.

** Also affects: nova/stein
   Importance: Undecided
       Status: New

** Also affects: nova/queens
   Importance: Undecided
       Status: New

** Also affects: nova/train
   Importance: Undecided
       Status: New

** Also affects: nova/rocky
   Importance: Undecided
       Status: New

** Changed in: nova/queens
   Importance: Undecided => Low

** Changed in: nova/rocky
   Importance: Undecided => Low

** Changed in: nova/stein
   Importance: Undecided => Low

** Changed in: nova/train
   Importance: Undecided => Low

** Changed in: nova/queens
       Status: New => Triaged

** Changed in: nova/rocky
       Status: New => Triaged

** Changed in: nova/train
       Status: New => Triaged

** Changed in: nova/stein
       Status: New => Triaged

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You received this bug notification because you are a member of Yahoo!
Engineering Team, which is subscribed to OpenStack Compute (nova).
https://bugs.launchpad.net/bugs/1847367

Title:
  Images with hw:vif_multiqueue_enabled can be limited to 8 queues even
  if more are supported

Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) queens series:
  Triaged
Status in OpenStack Compute (nova) rocky series:
  Triaged
Status in OpenStack Compute (nova) stein series:
  Triaged
Status in OpenStack Compute (nova) train series:
  Triaged

Bug description:
  Nova version: 18.2.3
  Release: Rocky
  Compute node OS: CentOS 7.3
  Compute node kernel: 3.10.0-327.13.1.el7.x86_64

  In https://bugs.launchpad.net/nova/+bug/1570631 and commit
  https://review.opendev.org/#/c/332660/, a bug was fixed by making the
  assumption that the kernel version should also dictate the max number
  of queues on the tap interface when setting
  hw:vif_multiqueue_enabled=True. It was decided that 3.x kernels have a
  max queue count of 8. Unfortunately not all distributions follow this,
  and CentOS/RHEL has supported up to 256 queues since at least 7.2 even
  with a 3.x kernel.

  The result of this is that a 20 core VM created in Mitaka will have 20
  queues enabled (because the limit of 8 had not been added). The very
  same host after being upgraded to Rocky will instead only give 8
  queues to the VM even though the kernel supports 256.

  Could a workaround option be implemented to disable this check, or
  manually define the max queue count?

  Snippet of drivers/net/tun.c from CentOS 7.2 kernel source code:
  /* MAX_TAP_QUEUES 256 is chosen to allow rx/tx queues to be equal
   * to max number of VCPUs in guest. */
  #define MAX_TAP_QUEUES 256
  #define MAX_TAP_FLOWS  4096

  Snippet from the 3.10.0 kernel code from https://elixir.bootlin.com/linux/v3.10/source/drivers/net/tun.c:
  /* DEFAULT_MAX_NUM_RSS_QUEUES were choosed to let the rx/tx queues allocated for
   * the netdevice to be fit in one page. So we can make sure the success of
   * memory allocation. TODO: increase the limit. */
  #define MAX_TAP_QUEUES DEFAULT_MAX_NUM_RSS_QUEUES
  #define MAX_TAP_FLOWS  4096

  In the above example, DEFAULT_MAX_NUM_RSS_QUEUES is set to 8.

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