Set default of api_workers to number of CPUs

The current default for api_workers is 0.  This patch changes it to
use the number of CPUs available, which is the default that will
provide best performance.  This is consistent with some other
OpenStack service (Nova and Swift, at least, perhaps others).

Note that devstack is updated in another patch to ensure multiple API
workers is being tested for Neutron the same way it's tested for
several other services:

    https://review.openstack.org/140482

Co-Authored-By: Eugene Nikanorov <enikanorov@mirantis.com>
DocImpact
UpgradeImpact
Change-Id: I4d76baf68b014fc80693f53874734783089abda2

etc/neutron.conf

@@ -201,10 +201,12 @@ lock_path = $state_path/lock
 # =========== end of items for l3 extension =======
 
 # =========== WSGI parameters related to the API server ==============
-# Number of separate worker processes to spawn.  The default, 0, runs the
+# Number of separate worker processes to spawn.  A value of 0 runs the
 # worker thread in the current process.  Greater than 0 launches that number of
-# child processes as workers.  The parent process manages them.
-# api_workers = 0
+# child processes as workers.  The parent process manages them.  If not
+# specified, the default value is equal to the number of CPUs available to
+# achieve best performance.
+# api_workers = <number of CPUs>
 
 # Number of separate RPC worker processes to spawn.  The default, 0, runs the
 # worker thread in the current process.  Greater than 0 launches that number of

neutron/service.py

@@ -18,6 +18,7 @@ import logging as std_logging
 import os
 import random
 
+from oslo_concurrency import processutils
 from oslo_config import cfg
 from oslo_log import log as logging
 from oslo_messaging import server as rpc_server
@@ -40,8 +41,9 @@ service_opts = [
                default=40,
                help=_('Seconds between running periodic tasks')),
     cfg.IntOpt('api_workers',
-               default=0,
-               help=_('Number of separate API worker processes for service')),
+               help=_('Number of separate API worker processes for service. '
+                      'If not specified, the default is equal to the number '
+                      'of CPUs available for best performance.')),
     cfg.IntOpt('rpc_workers',
                default=0,
                help=_('Number of RPC worker processes for service')),
@@ -165,6 +167,13 @@ def serve_rpc():
                               'details.'))
 
 
+def _get_api_workers():
+    workers = cfg.CONF.api_workers
+    if workers is None:
+        workers = processutils.get_worker_count()
+    return workers
+
+
 def _run_wsgi(app_name):
     app = config.load_paste_app(app_name)
     if not app:
@@ -172,7 +181,7 @@ def _run_wsgi(app_name):
         return
     server = wsgi.Server("Neutron")
     server.start(app, cfg.CONF.bind_port, cfg.CONF.bind_host,
-                 workers=cfg.CONF.api_workers)
+                 workers=_get_api_workers())
     # Dump all option values here after all options are parsed
     cfg.CONF.log_opt_values(LOG, std_logging.DEBUG)
     LOG.info(_LI("Neutron service started, listening on %(host)s:%(port)s"),

neutron/tests/functional/test_service.py

@@ -0,0 +1,31 @@
+# Copyright 2014 Red Hat, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from oslo_concurrency import processutils
+from oslo_config import cfg
+
+from neutron import service
+from neutron.tests import base
+
+
+class TestService(base.BaseTestCase):
+
+    def test_api_workers_default(self):
+        self.assertEqual(processutils.get_worker_count(),
+                         service._get_api_workers())
+
+    def test_api_workers_from_config(self):
+        cfg.CONF.set_override('api_workers', 1234)
+        self.assertEqual(1234,
+                         service._get_api_workers())