Reduce config access in scheduler

Caching the configuration appears to make a impact on the time spent
in the scheduler. These config values reduce the time spent down from
around 5ms to around 4ms per request, when with 200 hosts.

Change-Id: I433cbbdbef4ac3c01a3e2b6ed5cf092a5cce6372

nova/scheduler/filters/ram_filter.py

@@ -67,9 +67,10 @@ class BaseRamFilter(filters.BaseHostFilter):
 
 class RamFilter(BaseRamFilter):
     """Ram Filter with over subscription flag."""
+    ram_allocation_ratio = CONF.ram_allocation_ratio
 
     def _get_ram_allocation_ratio(self, host_state, filter_properties):
-        return CONF.ram_allocation_ratio
+        return self.ram_allocation_ratio
 
 
 class AggregateRamFilter(BaseRamFilter):

nova/servicegroup/drivers/db.py

@@ -35,6 +35,7 @@ class DbDriver(api.ServiceGroupDriver):
     def __init__(self, *args, **kwargs):
         self.db_allowed = kwargs.get('db_allowed', True)
         self.conductor_api = conductor.API(use_local=self.db_allowed)
+        self.service_down_time = CONF.service_down_time
 
     def join(self, member_id, group_id, service=None):
         """Join the given service with it's group."""
@@ -67,7 +68,7 @@ class DbDriver(api.ServiceGroupDriver):
             last_heartbeat = last_heartbeat.replace(tzinfo=None)
         # Timestamps in DB are UTC.
         elapsed = timeutils.delta_seconds(last_heartbeat, timeutils.utcnow())
-        is_up = abs(elapsed) <= CONF.service_down_time
+        is_up = abs(elapsed) <= self.service_down_time
         if not is_up:
             msg = _('Seems service is down. Last heartbeat was %(lhb)s. '
                     'Elapsed time is %(el)s')

nova/tests/scheduler/test_host_filters.py

@@ -27,6 +27,7 @@ from nova.openstack.common import timeutils
 from nova.pci import pci_stats
 from nova.scheduler import filters
 from nova.scheduler.filters import extra_specs_ops
+from nova.scheduler.filters import ram_filter
 from nova.scheduler.filters import trusted_filter
 from nova import servicegroup
 from nova import test
@@ -499,7 +500,7 @@ class HostFiltersTestCase(test.NoDBTestCase):
     def test_ram_filter_fails_on_memory(self):
         self._stub_service_is_up(True)
         filt_cls = self.class_map['RamFilter']()
-        self.flags(ram_allocation_ratio=1.0)
+        ram_filter.RamFilter.ram_allocation_ratio = 1.0
         filter_properties = {'instance_type': {'memory_mb': 1024}}
         service = {'disabled': False}
         host = fakes.FakeHostState('host1', 'node1',
@@ -510,7 +511,7 @@ class HostFiltersTestCase(test.NoDBTestCase):
     def test_ram_filter_passes(self):
         self._stub_service_is_up(True)
         filt_cls = self.class_map['RamFilter']()
-        self.flags(ram_allocation_ratio=1.0)
+        ram_filter.RamFilter.ram_allocation_ratio = 1.0
         filter_properties = {'instance_type': {'memory_mb': 1024}}
         service = {'disabled': False}
         host = fakes.FakeHostState('host1', 'node1',
@@ -521,7 +522,7 @@ class HostFiltersTestCase(test.NoDBTestCase):
     def test_ram_filter_oversubscribe(self):
         self._stub_service_is_up(True)
         filt_cls = self.class_map['RamFilter']()
-        self.flags(ram_allocation_ratio=2.0)
+        ram_filter.RamFilter.ram_allocation_ratio = 2.0
         filter_properties = {'instance_type': {'memory_mb': 1024}}
         service = {'disabled': False}
         host = fakes.FakeHostState('host1', 'node1',