Make start_instance cast directly to compute host

Fixes bug 918615

start_instance doesn't need to go through scheduler because it still has
instance['host'] set and resources are still accounted for in the
scheduler, which means there's still room to restart it on its assigned
host (even though it is deleted from the virt layer)

Change-Id: I3cdd73b7ad2297b57f7e36be84819ff233ac8f08

nova/scheduler/multi.py

@@ -36,7 +36,6 @@ flags.DEFINE_string('volume_scheduler_driver',
 
 # A mapping of methods to topics so we can figure out which driver to use.
 _METHOD_MAP = {'run_instance': 'compute',
-               'start_instance': 'compute',
                'prep_resize': 'compute',
                'live_migration': 'compute',
                'create_volume': 'volume',

nova/scheduler/simple.py

@@ -100,13 +100,6 @@ class SimpleScheduler(chance.ChanceScheduler):
             del request_spec['instance_properties']['uuid']
         return instances
 
-    def schedule_start_instance(self, context, instance_id, *_args, **_kwargs):
-        instance_ref = db.instance_get(context, instance_id)
-        host = self._schedule_instance(context, instance_ref,
-                *_args, **_kwargs)
-        driver.cast_to_compute_host(context, host, 'start_instance',
-                instance_id=instance_id, **_kwargs)
-
     def schedule_create_volume(self, context, volume_id, *_args, **_kwargs):
         """Picks a host that is up and has the fewest volumes."""
         elevated = context.elevated()

nova/tests/scheduler/test_multi_scheduler.py

@@ -31,7 +31,10 @@ class FakeComputeScheduler(driver.Scheduler):
     def schedule_run_instance(self, *args, **kwargs):
         pass
 
-    def schedule_start_instance(self, *args, **kwargs):
+    def schedule_live_migration(self, *args, **kwargs):
+        pass
+
+    def schedule_prep_resize(self, *args, **kwargs):
         pass
 
     def schedule(self, *args, **kwargs):
@@ -76,7 +79,7 @@ class MultiDriverTestCase(test_scheduler.SchedulerTestCase):
         compute_driver = mgr.drivers['compute']
         volume_driver = mgr.drivers['volume']
 
-        test_methods = {compute_driver: ['run_instance', 'start_instance'],
+        test_methods = {compute_driver: ['run_instance', 'prep_resize'],
                         volume_driver: ['create_volume', 'create_volumes']}
 
         for driver, methods in test_methods.iteritems():