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[OpenStack Infra <2073528@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/c/openstack/nova/+/924427
Committed: https://opendev.org/openstack/nova/commit/757c333c0e55df4bcaf9d442fbe8dc8009e36989
Submitter: "Zuul (22348)"
Branch:    master

commit 757c333c0e55df4bcaf9d442fbe8dc8009e36989
Author: Sylvain Bauza <sbauza@xxxxxxxxxx>
Date:   Thu Jul 18 19:08:49 2024 +0200

    cpu: Only check governor type on online cores
    
    Kernels don't accept to access the governor strategy on an offline core, so
    we need to only validate strategies for online cores.
    
    Change-Id: I14c9b268d0b97221216bd1a9ab9e48b48d6dcc2c
    Closes-Bug: #2073528


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/2073528

Title:
  Restarting nova-compute fails if power management is enabled

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  The nova-compute fails to start up on a physical hardware if power management is enabled, dedicated cpus are configured, and the nova-compute is restarted (initial start works).
  When the strategy is cpu_state then:

  - the nova-compute code reads the cpu state and governor values of the dedicated cpus at startup
  - then offline all the unallocated dedicated cores (except cpu0)
  - then when nova-compute is restarted
  - nova tries to read the governor from an offlined cpus and that is not supported by the kernel on a physical core, so nova fails to start up.

  https://github.com/openstack/nova/blob/master/nova/virt/libvirt/driver.py#L853-L859
  https://github.com/openstack/nova/blob/master/nova/virt/libvirt/cpu/api.py#L186
  physical hardware
  root@bedrock:/home/gibi# cat /sys/devices/system/cpu/cpu4/online
  1
  root@bedrock:/home/gibi# cat /sys/devices/system/cpu/cpu4/cpufreq/scaling_governor
  powersave
  root@bedrock:/home/gibi# echo 0 > /sys/devices/system/cpu/cpu4/online
  root@bedrock:/home/gibi# cat /sys/devices/system/cpu/cpu4/cpufreq/scaling_governor
  cat: /sys/devices/system/cpu/cpu4/cpufreq/scaling_governor: Device or resource busy
  root@bedrock:/home/gibi#

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