Enable bulk updates for the dnsmasq

Instead of restarting the dnsmasq agent for every IP we do this
in bulk. That is, if a network has N updates in X seconds then we will
restart the process once with the ports configured in the X seconds and
not N Times.

A new configuration variable have been added:

- bulk_reload_interval - time to wait between bulk reloads. This is 0 by
  default to ensure backwards compatibility. If the value is not 0 the
  new functionlay is invoked.

Change-Id: Ieff5ce4506fd4e7fa427eb50c50fbe316f67103f

neutron/agent/dhcp/agent.py

@@ -115,6 +115,7 @@ class DhcpAgent(manager.Manager):
         self._pool_size = DHCP_PROCESS_GREENLET_MIN
         self._pool = eventlet.GreenPool(size=self._pool_size)
         self._queue = queue.ResourceProcessingQueue()
+        self._network_bulk_allocations = {}
 
     def init_host(self):
         self.sync_state()
@@ -144,11 +145,27 @@ class DhcpAgent(manager.Manager):
         self.periodic_resync()
         self.start_ready_ports_loop()
         eventlet.spawn_n(self._process_loop)
+        if self.conf.bulk_reload_interval:
+            eventlet.spawn_n(self._reload_bulk_allocations)
+
+    def _reload_bulk_allocations(self):
+        while True:
+            for network_id in self._network_bulk_allocations.keys():
+                network = self.cache.get_network_by_id(network_id)
+                self.call_driver('bulk_reload_allocations', network)
+                del self._network_bulk_allocations[network_id]
+            eventlet.greenthread.sleep(self.conf.bulk_reload_interval)
 
     def call_driver(self, action, network, **action_kwargs):
         """Invoke an action on a DHCP driver instance."""
         LOG.debug('Calling driver for network: %(net)s action: %(action)s',
                   {'net': network.id, 'action': action})
+        if self.conf.bulk_reload_interval and action == 'reload_allocations':
+            LOG.debug("Call deferred to bulk load")
+            self._network_bulk_allocations[network.id] = True
+            return True
+        if action == 'bulk_reload_allocations':
+            action = 'reload_allocations'
         try:
             # the Driver expects something that is duck typed similar to
             # the base models.

neutron/conf/agent/dhcp.py

@@ -68,7 +68,13 @@ DHCP_AGENT_OPTS = [
     cfg.IntOpt('num_sync_threads', default=4,
                help=_('Number of threads to use during sync process. '
                       'Should not exceed connection pool size configured on '
-                      'server.'))
+                      'server.')),
+    cfg.IntOpt('bulk_reload_interval', default=0, min=0,
+               help=_('Time to sleep between reloading the DHCP allocations. '
+                      'This will only be invoked if the value is not 0. '
+                      'If a network has N updates in X seconds then '
+                      'we will reload once with the port changes in the X '
+                      'seconds and not N times.')),
 ]
 
 DHCP_OPTS = [

releasenotes/notes/dhcp-bulk-updates-0150b764bb1b165f.yaml

@@ -0,0 +1,14 @@
+---
+features:
+  - By default the dnsmasq agent is restarted for every
+    port created, deleted or updated. When there are
+    many port changes on the same network it can and will
+    take a very long time for all of the port changes to
+    be realised. This enhancement adds in a new
+    configuration variable that will enable bulk updates.
+    This means that the dnsmasq will only be restarted once
+    in a period and not N times.
+    The new option 'bulk_reload_interval' indicates how
+    often the agent should be reloaded. The default value
+    is 0 which means that the original functionality is the
+    default.