From b880153f078255eb770ff1bb79335f533b8dcac4 Mon Sep 17 00:00:00 2001
From: Adam Gandelman <adamg@ubuntu.com>
Date: Tue, 24 Jun 2014 15:34:42 -0700
Subject: [PATCH] Update Nova's available resources at termination

This updates ClusteredComputeManager to override terminate_instance() with
a call to update_available_resource().  The goal here is to limit the lag
between when an Ironic node has been freed and when it will become available
again to the Nova.  This avoids scheduling errors against Ironic node
inventories with high utilization and/or limited node resources.

Change-Id: I767cb97d9b182f1f9528d078b07a85ffbad313ba
Closes-bug: #1334027
---
 ironic/nova/compute/manager.py | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/ironic/nova/compute/manager.py b/ironic/nova/compute/manager.py
index b764e49a7f..1e2d04f50a 100644
--- a/ironic/nova/compute/manager.py
+++ b/ironic/nova/compute/manager.py
@@ -23,10 +23,14 @@ work. The goal here is to generalise the areas where n-c talking to a clustered
 hypervisor has issues, and long term fold them into the main ComputeManager.
 """
 
+from nova.openstack.common import lockutils
 from nova.compute import manager
 import nova.context
 
 
+CCM_SEMAPHORE='clustered_compute_manager'
+
+
 class ClusteredComputeManager(manager.ComputeManager):
 
     def init_host(self):
@@ -73,3 +77,23 @@ class ClusteredComputeManager(manager.ComputeManager):
             self.update_available_resource(nova.context.get_admin_context())
         except Exception:
             pass
+
+    @lockutils.synchronized(CCM_SEMAPHORE, 'ironic-')
+    def _update_resources(self):
+        """Updates resources while protecting against a race on
+        self._resource_tracker_dict.
+        """
+        self.update_available_resource(nova.context.get_admin_context())
+
+    def terminate_instance(self, context, instance, bdms, reservations):
+        """Terminate an instance on a node.
+
+        We override this method and force a post-termination update to Nova's
+        resources. This avoids having to wait for a Nova periodic task tick
+        before nodes can be reused.
+        """
+        super(ClusteredComputeManager, self).terminate_instance(context,
+                                                                instance,
+                                                                bdms,
+                                                                reservations)
+        self._update_resources()