update default overcommit

This change updates the cpu and ram initial
allocation ratios to 4.0 and 1.0 to reflect
the typical values that are suitable for non web
hosting workloads.

Change-Id: I283eb270a4e47da15cf01d098b4f3952f7b5b570
implements: bp/nova-change-default-overcommit-values

Author: SeanMooney

doc/source/admin/scheduling.rst

@@ -1100,6 +1100,16 @@ control the initial allocation ratio values for a compute node:
 * :oslo.config:option:`initial_disk_allocation_ratio` the initial DISK_GB
   inventory allocation ratio for a new compute node record, defaults to 1.0
 
+Starting with the 27.0.0 Antelope release, the following default values are used
+for the initial allocation ratio values for a compute node:
+
+* :oslo.config:option:`initial_cpu_allocation_ratio` the initial VCPU
+  inventory allocation ratio for a new compute node record, defaults to 4.0
+* :oslo.config:option:`initial_ram_allocation_ratio` the initial MEMORY_MB
+  inventory allocation ratio for a new compute node record, defaults to 1.0
+* :oslo.config:option:`initial_disk_allocation_ratio` the initial DISK_GB
+  inventory allocation ratio for a new compute node record, defaults to 1.0
+
 Scheduling considerations
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 

nova/conf/compute.py

@@ -529,7 +529,7 @@
 * ``initial_disk_allocation_ratio``
 """),
     cfg.FloatOpt('initial_cpu_allocation_ratio',
-                 default=16.0,
+                 default=4.0,
                  min=0.0,
                  help="""
 Initial virtual CPU to physical CPU allocation ratio.
@@ -545,7 +545,7 @@
 * ``cpu_allocation_ratio``
 """),
     cfg.FloatOpt('initial_ram_allocation_ratio',
-                 default=1.5,
+                 default=1.0,
                  min=0.0,
                  help="""
 Initial virtual RAM to physical RAM allocation ratio.

nova/tests/functional/test_server_group.py

@@ -103,7 +103,10 @@ class ServerGroupFakeDriver(fake.SmallFakeDriver):
     """
 
     vcpus = 1000
-    memory_mb = 8192
+    # the testcases were built with a default ram allocation ratio
+    # of 1.5 and 8192 mb of ram so to maintain the same capacity with
+    # the new default allocation ratio of 1.0 we use 8192+4096=12288
+    memory_mb = 12288
     local_gb = 100000
 
 

nova/tests/functional/test_servers_provider_tree.py

@@ -82,15 +82,15 @@ def setUp(self):
             },
             'MEMORY_MB': {
                 'total': 8192,
-                'allocation_ratio': 1.5,
+                'allocation_ratio': 1.0,
                 'max_unit': 8192,
                 'min_unit': 1,
                 'reserved': 512,
                 'step_size': 1,
             },
             'VCPU': {
                 'total': 10,
-                'allocation_ratio': 16.0,
+                'allocation_ratio': 4.0,
                 'max_unit': 10,
                 'min_unit': 1,
                 'reserved': 0,

nova/tests/unit/objects/test_compute_node.py

@@ -666,8 +666,8 @@ def test_compat_allocation_ratios_zero_conf(self, mock_update):
             CONF.initial_disk_allocation_ratio, compute.disk_allocation_ratio)
 
         mock_update.assert_called_once_with(
-            self.context, 123, {'cpu_allocation_ratio': 16.0,
-                                'ram_allocation_ratio': 1.5,
+            self.context, 123, {'cpu_allocation_ratio': 4.0,
+                                'ram_allocation_ratio': 1.0,
                                 'disk_allocation_ratio': 1.0})
 
     @mock.patch('nova.db.main.api.compute_node_update')
@@ -694,8 +694,8 @@ def test_compat_allocation_ratios_None_conf_zero_values(self, mock_update):
             CONF.initial_disk_allocation_ratio, compute.disk_allocation_ratio)
 
         mock_update.assert_called_once_with(
-            self.context, 123, {'cpu_allocation_ratio': 16.0,
-                                'ram_allocation_ratio': 1.5,
+            self.context, 123, {'cpu_allocation_ratio': 4.0,
+                                'ram_allocation_ratio': 1.0,
                                 'disk_allocation_ratio': 1.0})
 
     @mock.patch('nova.db.main.api.compute_node_update')
@@ -722,8 +722,8 @@ def test_compat_allocation_ratios_None_conf_None_values(self, mock_update):
             CONF.initial_disk_allocation_ratio, compute.disk_allocation_ratio)
 
         mock_update.assert_called_once_with(
-            self.context, 123, {'cpu_allocation_ratio': 16.0,
-                                'ram_allocation_ratio': 1.5,
+            self.context, 123, {'cpu_allocation_ratio': 4.0,
+                                'ram_allocation_ratio': 1.0,
                                 'disk_allocation_ratio': 1.0})
 
     def test_get_all_by_not_mapped(self):

nova/tests/unit/virt/libvirt/test_driver.py

@@ -21366,7 +21366,7 @@ def _get_inventory(self):
                 'min_unit': 1,
                 'max_unit': self.vcpus,
                 'step_size': 1,
-                'allocation_ratio': 16.0,
+                'allocation_ratio': 4.0,
                 'reserved': 0,
             },
             orc.PCPU: {
@@ -21382,7 +21382,7 @@ def _get_inventory(self):
                 'min_unit': 1,
                 'max_unit': self.memory_mb,
                 'step_size': 1,
-                'allocation_ratio': 1.5,
+                'allocation_ratio': 1.0,
                 'reserved': 512,
             },
             orc.DISK_GB: {

nova/tests/unit/virt/vmwareapi/test_driver_api.py

@@ -2123,15 +2123,15 @@ def test_update_provider_tree(self, mock_get_avail_ds):
                 'min_unit': 1,
                 'max_unit': 16,
                 'step_size': 1,
-                'allocation_ratio': 16.0,
+                'allocation_ratio': 4.0,
             },
             orc.MEMORY_MB: {
                 'total': 2048,
                 'reserved': 512,
                 'min_unit': 1,
                 'max_unit': 1024,
                 'step_size': 1,
-                'allocation_ratio': 1.5,
+                'allocation_ratio': 1.0,
             },
             orc.DISK_GB: {
                 'total': 95,

releasenotes/notes/update-initial-allocation-defaults-94106033b66b8fa0.yaml

@@ -0,0 +1,21 @@
+---
+upgrade:
+  - |
+    In this release the default values for the initial ram and cpu allocation
+    ratios have been updated to 1.0 and 4.0 respectively. This will not
+    affect any existing compute node resource providers but the new default
+    will take effect on the creation of new resource providers.
+other:
+  - |
+    The default initial allocation ratios enabled ram over commit by default
+    with a factor of ``1.5``. This value was chosen early in nova's history
+    as the predominant workload was web hosting or other light weight
+    virtualization. Similarly the default initial cpu allocation ratio
+    defaulted to 16. As more demanding workload from telco, enterprise,
+    scientific and governmental users became the norm the initial values we
+    had chosen became less and less correct overtime. These have now been
+    updated to reflect a more reasonable default for the majority of our users.
+    As of this release the initial ram allocation value is 1.0 disabling
+    overcommit by default for new compute nodes and the initial cpu allocation
+    ratio is now 4.0 which is a more reasonable overcommit for non idle
+    workloads.