Merge "Scheduler multiple workers support"

nova/cmd/scheduler.py

@@ -18,6 +18,7 @@
 
 import sys
 
+from oslo_concurrency import processutils
 from oslo_log import log as logging
 from oslo_reports import guru_meditation_report as gmr
 from oslo_reports import opts as gmr_opts
@@ -45,5 +46,11 @@ def main():
 
     server = service.Service.create(binary='nova-scheduler',
                                     topic=scheduler_rpcapi.RPC_TOPIC)
-    service.serve(server)
+    # Determine the number of workers; if not specified in config, default
+    # to ncpu for the FilterScheduler and 1 for everything else.
+    workers = CONF.scheduler.workers
+    if not workers:
+        workers = (processutils.get_worker_count()
+                   if CONF.scheduler.driver == 'filter_scheduler' else 1)
+    service.serve(server, workers=workers)
     service.wait()

nova/conf/scheduler.py

@@ -63,6 +63,10 @@ Possible values:
 * You may also set this to the entry point name of a custom scheduler driver,
   but you will be responsible for creating and maintaining it in your setup.cfg
   file.
+
+Related options:
+
+* workers
 """),
     cfg.IntOpt("periodic_task_interval",
         default=60,
@@ -139,6 +143,13 @@ etc. of the scheduler.
 
 This option is only used by the FilterScheduler; if you use a different
 scheduler, this option has no effect.
+"""),
+    cfg.IntOpt("workers",
+        min=0,
+        help="""
+Number of workers for the nova-scheduler service. The default will be the
+number of CPUs available if using the "filter_scheduler" scheduler driver,
+otherwise the default will be 1.
 """),
 ]
 

nova/tests/unit/cmd/test_scheduler.py

@@ -0,0 +1,61 @@
+# 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.
+
+import mock
+
+from nova.cmd import scheduler
+from nova import config
+from nova import test
+
+
+# required because otherwise oslo early parse_args dies
+@mock.patch.object(config, 'parse_args', new=lambda *args, **kwargs: None)
+class TestScheduler(test.NoDBTestCase):
+
+    @mock.patch('nova.service.Service.create')
+    @mock.patch('nova.service.serve')
+    @mock.patch('nova.service.wait')
+    @mock.patch('oslo_concurrency.processutils.get_worker_count',
+                return_value=2)
+    def test_workers_defaults(self, get_worker_count, mock_wait, mock_serve,
+                              service_create):
+        scheduler.main()
+        get_worker_count.assert_called_once_with()
+        mock_serve.assert_called_once_with(
+            service_create.return_value, workers=2)
+        mock_wait.assert_called_once_with()
+
+    @mock.patch('nova.service.Service.create')
+    @mock.patch('nova.service.serve')
+    @mock.patch('nova.service.wait')
+    @mock.patch('oslo_concurrency.processutils.get_worker_count')
+    def test_workers_override(self, get_worker_count, mock_wait, mock_serve,
+                              service_create):
+        self.flags(workers=4, group='scheduler')
+        scheduler.main()
+        get_worker_count.assert_not_called()
+        mock_serve.assert_called_once_with(
+            service_create.return_value, workers=4)
+        mock_wait.assert_called_once_with()
+
+    @mock.patch('nova.service.Service.create')
+    @mock.patch('nova.service.serve')
+    @mock.patch('nova.service.wait')
+    @mock.patch('oslo_concurrency.processutils.get_worker_count')
+    def test_workers_caching_scheduler(self, get_worker_count, mock_wait,
+                                       mock_serve, service_create):
+        self.flags(driver='caching_scheduler', group='scheduler')
+        scheduler.main()
+        get_worker_count.assert_not_called()
+        mock_serve.assert_called_once_with(
+            service_create.return_value, workers=1)
+        mock_wait.assert_called_once_with()

releasenotes/notes/multiple-scheduler-workers-3e5ac0d86f436338.yaml

@@ -0,0 +1,26 @@
+---
+features:
+  - |
+    It is now possible to configure multiple *nova-scheduler* workers via the
+    ``[scheduler]workers`` configuration option. By default, the option runs
+    ``ncpu`` workers if using the ``filter_scheduler`` scheduler driver,
+    otherwise the default is 1.
+
+    Since `blueprint placement-claims`_ in Pike, the FilterScheduler
+    uses the Placement service to create resource allocations (claims)
+    against a resource provider (i.e. compute node) chosen by the scheduler.
+    That reduces the risk of scheduling collisions when running multiple
+    schedulers.
+
+    Since other scheduler drivers, like the CachingScheduler, do not
+    use Placement, it is recommended to set workers=1 (default) for those
+    other scheduler drivers.
+
+    .. _blueprint placement-claims: https://specs.openstack.org/openstack/nova-specs/specs/pike/implemented/placement-claims.html
+upgrade:
+  - |
+    The new ``[scheduler]workers`` configuration option defaults to ``ncpu``
+    workers if using the ``filter_scheduler`` scheduler driver. If you are
+    running *nova-scheduler* on the same host as other services, you may want
+    to change this default value, or to otherwise account for running other
+    instances of the *nova-scheduler* service.