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[Artom Lifshitz <1978489@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

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

** Affects: nova
     Importance: Undecided
         Status: In Progress

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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

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

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