Open Stack

* COMPUTE_RESOURCE_SEMAPHORE blocks instance creation on all nodes (on 
the same host) while the _update_available_resource runs on all nodes. 
On 3500 baremetal nodes _update_available_resource takes 1.5 hour.
* Do we still need _update_available_resource periodic task to run for 
ironic nodes?
* Reduce the scope of the COMPUTE_RESOURCE_SEMAPHORE lock
  * https://review.opendev.org/#/c/682242/
  * https://review.opendev.org/#/c/677790/
* changing a locking scheme is frightening => we need more testing

Agreement:
* Do a tempest test with a lot of fake ironic node records to have a 
way to test if changing the locking scheme breaks anything
* Log a bug and propose a patch for having a per-node lock instead of 
the same object for all the ResourceTrackers
* See also whether concurrency helps
* Propose a spec if you really want to pursue the idea of being somehow 
inconsistent with data by not having a lock

Cheers,
gibi