[Bug 1978489] Re: libvirt / cgroups v2: cannot boot instance with more than 16 CPUs

[Steve Langasek]

Hello Artom, or anyone else affected,

Accepted nova into jammy-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/nova/3:25.2.1-0ubuntu2
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
jammy to verification-done-jammy. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-jammy. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: nova (Ubuntu Jammy)
       Status: Triaged => Fix Committed

** Tags added: verification-needed verification-needed-jammy

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https://bugs.launchpad.net/bugs/1978489

Title:
  libvirt / cgroups v2: cannot boot instance with more than 16 CPUs

Status in OpenStack Compute (nova):
  In Progress
Status in nova package in Ubuntu:
  Confirmed
Status in nova source package in Jammy:
  Fix Committed

Bug description:
  Description
  ===========

  Using the libvirt driver and a host OS that uses cgroups v2 (RHEL 9,
  Ubuntu Jammy), an instance with more than 16 CPUs cannot be booted.

  Steps to reproduce
  ==================

  1. Boot an instance with 10 (or more) CPUs on RHEL 9 or Ubuntu Jammy
  using Nova with the libvirt driver.

  Expected result
  ===============

  Instance boots.

  Actual result
  =============

  Instance fails to boot with a 'Value specified in CPUWeight is out of
  range' error.

  Environment
  ===========

  Originially report as a libvirt but in RHEL 9 [1]

  Additional information
  ======================

  This is happening because Nova defaults to 1024 * (# of CPUs) for the
  value of domain/cputune/shares in the libvirt XML. This is then passed
  directly by libvirt to the cgroups API, but cgroups v2 has a maximum
  value of 10000. 10000 / 1024 ~= 9.76

  [1] https://bugzilla.redhat.com/show_bug.cgi?id=2035518

  
  ====================================

  Ubuntu SRU Details:

  [Impact]
  See above.

  [Test Case]
  See above.

  [Regression Potential]
  We've had this change in other jammy-based versions of the nova package for a while now, including zed, antelope, bobcat.

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