Default engine workers to the number of CPUs

The engine is single-threaded and thus needs more workers to handle more
concurrent requests on a single machine.

Change-Id: I36117c3876f84a2ff7ba5576444fdbf7716cc69e

bin/heat-engine

@@ -21,6 +21,7 @@ which then calls into this engine.
 import eventlet
 eventlet.monkey_patch()
 
+import multiprocessing
 import os
 import sys
 
@@ -61,7 +62,11 @@ if __name__ == '__main__':
 
     from heat.engine import service as engine
 
+    num_workers = cfg.CONF.num_engine_workers
+    if num_workers == -1:
+        num_workers = multiprocessing.cpu_count()
+
     srv = engine.EngineService(cfg.CONF.host, rpc_api.ENGINE_TOPIC)
-    launcher = service.launch(srv, workers=cfg.CONF.num_engine_workers)
+    launcher = service.launch(srv, workers=num_workers)
     notify.startup_notify(cfg.CONF.onready)
     launcher.wait()

heat/common/config.py

@@ -77,8 +77,9 @@ service_opts = [
                default=3,
                help='Maximum depth allowed when using nested stacks.'),
     cfg.IntOpt('num_engine_workers',
-               default=1,
-               help='Number of heat-engine processes to fork and run.')]
+               default=-1,
+               help='Number of heat-engine processes to fork and run. -1'
+                    ' will spawn a worker for each CPU on the machine')]
 
 engine_opts = [
     cfg.StrOpt('instance_user',