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[Sylvain Bauza <2073528@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

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#

** Affects: nova
     Importance: Medium
     Assignee: Sylvain Bauza (sylvain-bauza)
         Status: New


** Tags: libvirt

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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):
  New

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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