As part of investigating https://bugs.launchpad.net/nova/+bug/1687067 someone referred me to https://docs.openstack.org/admin-guide/compute-cpu-topologies.html where it says "Image metadata takes precedence over flavor extra specs."
This is generally not true, in fact it is exactly backwards. The flavors are created by administrator-level users, while images can be created by regular users. Thus, flavor extra-specs can be used to restrict what regular users are allowed to set in the image properties.
I looked through the docs for cases discussing mismatch between flavor extra-specs and image properties. I found three cases and in all three cases the docs did not match the code.
I'm proposing a fixup to deal with this.
There's one remaining piece that I haven't dealt with, which is what happens when the flavor specifies a cpu threading policy of "prefer" and the image specifies "isolate" or "require". This is still in discussion within the nova team, since the code behaviour was accidentally changed between Mitaka and Newton. Once the nova team sorts it out a final fix will be made to the docs in a separate commit.
Fix proposed to branch: master
Review: https:/