Comment 18 for bug 1978489

> This behavior can be recovered by setting the quota:cpu_shares flavor extra spec.

You are the openstack experts here, but I will point out that it looks like comment #10 already tried this.

That comment also ends with: "Is there any workaround to rebuilding hundreds of instances like force nova to override flavors of existing instances?"

Do we have a concrete answer for that? Like, "here is what you do, step by step".