Live migration between hosts with different CPU models fails

[Jesse Pendergrass]

Detailed bug description:
  The pre-migration cpu comparison check that is done during a live migration is too strict. For example, if you have one compute node with Broadwell cpu arch, and another with Broadwell-IBRS, then trying to live-migration from the IBRS version to the non-IBRS version will fail. Even when specifying a custom cpu mode and a specific cpu model in nova.conf, it will still fail for this reason.

Expected results:
  When specifying a custom cpu mode and a specific cpu model that exists in the baseline on both compute nodes, the live migration should not fail due to a comparison check failure like this.

Actual result:
  [root@bransible ansible]# openstack server migrate xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx --live node-##.abc123.local
  Migration pre-check error: CPU doesn't have compatibility.

  internal error: Unknown CPU model Broadwell-IBRS

  Refer to http://libvirt.org/html/libvirt-libvirt-host.html#virCPUCompareResult (HTTP 400) (Request-ID: req-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)

Workaround:
  https://bugs.launchpad.net/nova/+bug/1082414

  A workaround is available in this bug report in comment 20, but it requires making manual changes to the nova/virt/libvirt/driver.py file. Ideally, there should be a configuration flag that allows one to skip the pre-migration cpu comparison check, or the check should be less strict when nova is configured to use a common baseline cpu model.

Impact:
  - Users will have difficulty performing live migrations between older hardware and newer hardware.

Additional information:
  - Existing bug found here: https://bugs.launchpad.net/nova/+bug/1082414

[Denis Meltsaykin (dmeltsaykin)]

Please provide MOS version, also the bug you are referring to is fixed in kilo, this means it should also be fixed in all modern versions.

[Denis Meltsaykin (dmeltsaykin)]

No info provided in one month, I'm going to close it as Invalid. Feel free to re-open it if you have the needed information.

[Jesse Pendergrass (jpendergrass)]

"Please provide MOS version, also the bug you are referring to is fixed in kilo, this means it should also be fixed in all modern versions."

Please find the requested information below.

Deployment/LCM Version: MOS 9.2
Deployed Using: Puppet (Fuel)
OpenStack Packages Version: Mitaka
Host OS: Ubuntu 14.04

I understand that the fix for this was released in Kilo, however, as I recall the issue was still present in the client's Mitaka MOS 9.2. Let me know if any additional information is needed.