diff --git a/neutron/callbacks/events.py b/neutron/callbacks/events.py
index 4db83d85008..a253079914c 100644
--- a/neutron/callbacks/events.py
+++ b/neutron/callbacks/events.py
@@ -34,6 +34,7 @@ AFTER_REQUEST = 'after_request'
 # String literals representing events associated to process operations
 BEFORE_INIT = 'before_init'
 BEFORE_SPAWN = 'before_spawn'  # sent per process
+AFTER_SPAWN = 'after_spawn'  # sent per process
 AFTER_INIT = 'after_init'  # sent per worker
 
 # String literals representing events associated to error conditions
diff --git a/neutron/service.py b/neutron/service.py
index 4d4625b5ef6..9c71238c786 100644
--- a/neutron/service.py
+++ b/neutron/service.py
@@ -32,6 +32,7 @@ from oslo_utils import excutils
 from oslo_utils import importutils
 
 from neutron._i18n import _LE, _LI
+from neutron.callbacks import events as n_events
 from neutron.common import config
 from neutron.common import profiler
 from neutron.common import rpc as n_rpc
@@ -262,7 +263,10 @@ def _start_workers(workers):
 
 def start_all_workers():
     workers = _get_rpc_workers() + _get_plugins_workers()
-    return _start_workers(workers)
+    launcher = _start_workers(workers)
+    # TODO(yamahata): replace n_events with neutron_lib.callback.events
+    registry.notify(resources.PROCESS, n_events.AFTER_SPAWN, None)
+    return launcher
 
 
 def start_rpc_workers():
diff --git a/neutron/tests/unit/test_service.py b/neutron/tests/unit/test_service.py
index d05104b3704..31ffab2533e 100644
--- a/neutron/tests/unit/test_service.py
+++ b/neutron/tests/unit/test_service.py
@@ -15,8 +15,11 @@
 
 import mock
 
+from neutron_lib.callbacks import registry
+from neutron_lib.callbacks import resources
 from oslo_config import cfg
 
+from neutron.callbacks import events as n_events
 from neutron import service
 from neutron.tests import base
 from neutron.tests.unit import test_wsgi
@@ -55,3 +58,16 @@ class TestRunWsgiApp(base.BaseTestCase):
 
     def test_api_workers_defined(self):
         self._test_api_workers(42, 42)
+
+    def test_start_all_workers(self):
+        cfg.CONF.set_override('api_workers', 0)
+        mock.patch.object(service, '_get_rpc_workers').start()
+        mock.patch.object(service, '_get_plugins_workers').start()
+        mock.patch.object(service, '_start_workers').start()
+
+        callback = mock.Mock()
+        # TODO(yamahata): replace n_events with neutron_lib.callback.events
+        registry.subscribe(callback, resources.PROCESS, n_events.AFTER_SPAWN)
+        service.start_all_workers()
+        callback.assert_called_once_with(
+            resources.PROCESS, n_events.AFTER_SPAWN, mock.ANY)