Reproduction:

• have a deployment with pinned CPUs configured and power mgmt enabled

  [root@edpm-compute-0 ~]# podman exec -it nova_compute cat /etc/nova/nova.conf.d/25-cpu-pinning-nova.conf | egrep -e '_set|power' -B1
  [compute]
  cpu_shared_set = 0,1,2,3
  cpu_dedicated_set = 4-19
  --
    [libvirt]
  cpu_power_management=true
  

• check that nova-compute disabled the unused pcpus at startup

  On-line CPU(s) list:                0-3,20-255
  Off-line CPU(s) list:               4-19
  

• boot a VM with nova that using pinned CPUs

  [zuul@controller-0 ~]$ openstack flavor show m1.dedicated
  +----------------------------+--------------------------------------+
  | Field                      | Value                                |
  +----------------------------+--------------------------------------+
  | OS-FLV-DISABLED:disabled   | False                                |
  | OS-FLV-EXT-DATA:ephemeral  | 0                                    |
  | access_project_ids         | None                                 |
  | description                | None                                 |
  | disk                       | 1                                    |
  | id                         | 4e5abbfc-2cfc-4f13-a0b0-442aeb51ea7b |
  | name                       | m1.dedicated                         |
  | os-flavor-access:is_public | True                                 |
  | properties                 | hw:cpu_policy='dedicated'            |
  | ram                        | 512                                  |
  | rxtx_factor                | 1.0                                  |
  | swap                       |                                      |
  | vcpus                      | 2                                    |
  +----------------------------+--------------------------------------+
  
  [zuul@controller-0 ~]$ openstack --os-compute-api-version 2.80 server create --image cirros --flavor m1.dedicated --nic none vm1-gibi
  

• observe that nova onlined the two pcpus allocated to the VM

  [root@edpm-compute-0 ~]# virsh dumpxml 5 | grep vcpupin
      <vcpupin vcpu='0' cpuset='7'/>
      <vcpupin vcpu='1' cpuset='11'/>
  
  [root@edpm-compute-0 ~]# lscpu | grep 'line CPU'
  On-line CPU(s) list:                0-3,7,11,20-255
  Off-line CPU(s) list:               4-6,8-10,12-19
  
  [root@edpm-compute-0 ~]# taskset -cp `pgrep qemu-kvm`
  pid 130794's current affinity list: 7,11
  

• restart the nova-compute service

  [root@edpm-compute-0 ~]# systemctl restart edpm_nova_compute
  
  

• observe that the VM is still running, the allocated PCPU cores are offlined and the VM is unpinned

  [root@edpm-compute-0 ~]# virsh list 
   Id   Name                State
  -----------------------------------
   5    instance-00000007   running
  
  [root@edpm-compute-0 ~]# virsh dumpxml 5 | grep vcpupin
      <vcpupin vcpu='0' cpuset='7'/>
      <vcpupin vcpu='1' cpuset='11'/>
  
  [root@edpm-compute-0 ~]# lscpu | grep 'line CPU'
  On-line CPU(s) list:                0-3,20-255
  Off-line CPU(s) list:               4-19
  
  [root@edpm-compute-0 ~]# taskset -cp `pgrep qemu-kvm`
  pid 130794's current affinity list: 0-3,20-255
  

Expected behavior:

• nova-compute restart does not offline any PCPU that are used by running VMs.

Relevant nova-compute log during the service restart:

Oct 17 14:47:26 edpm-compute-0 nova_compute[130962]: 2024-10-17 14:47:26.544 2 DEBUG nova.virt.libvirt.cpu.api [None req-b2f86412-9ebd-44ae-9d0d-925cd6bcb7fd - - - - - -] Cores powered up : {'4', '15', '5', '6', '19', '10', '14', '17', '18', '11', '9', '16', '7', '8', '12', '13'} power_up /usr/lib/python3.9/site-packages/nova/virt/libvirt/cpu/api.py:107
Oct 17 14:47:28 edpm-compute-0 nova_compute[130962]: 2024-10-17 14:47:28.938 2 DEBUG nova.virt.libvirt.cpu.api [None req-b2f86412-9ebd-44ae-9d0d-925cd6bcb7fd - - - - - -] Cores powered down : {4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19} power_down_all_dedicated_cpus /usr/lib/python3.9/site-packages/nova/virt/libvirt/cpu/api.py:169

The whole restart log is attached as https://issues.redhat.com/secure/attachment/13283260/nova-compute-restart.log