Hey Folks,

We have a number of nodes in our openstack cluster who have the same family CPU (IvyBridge-IBRS) ... and one advanced CPU (Broadwell-IBRS). We have set the cpu_mode to custom and overridden the cpu_model to IvyBridge-IBRS so that all of the hosts would be compatible.

This seems to work for instances started on the advanced host... we can live migrate off of the host. But... when we live migrate instances TO the advanced host... they seem to inherit the wrong CPU type.

Example:

If I live migrated onto the advanced host and then try to live migrate off of it... nova-compute logs on the older host throw:

Error: Migration pre-check error: Unacceptable CPU info: CPU doesn't have compatibility.

And the output clearly shows that it thinks it was launched on the Broadwell CPU:

Instance launched has CPU info: {"arch": "x86_64", "model": "Broadwell- IBRS", "vendor": "Intel" ...

With that instance on the advanced host, if I restart it... magically it comes up with the correct cpu_model and can be live migrated off...

We're running ussuri ... does anyone know if this is known behavior? Could I have a misconfiguration somewhere?

Thanks.