Cap the number of worker threads

Users can configure the number of worker threads however when it's
not specified the calculated number of workers can get too large on
hosts with a large number of CPUs.

Change-Id: I10a653dda7444b756fede74ce434b9038415c74c

defaults/main.yml

@@ -441,15 +441,16 @@ neutron_quota_vip: 10
 
 ## General Neutron configuration
 # If ``neutron_api_workers`` is unset the system will use half the number of available VCPUs to
-# compute the number of api workers to use.
+# compute the number of api workers to use with a default capping value of 16.
 # neutron_api_workers: 16
 
 # If ``neutron_metadata_workers`` is unset the system will use half the number of available VCPUs to
-# compute the number of api workers to use.
+# compute the number of api workers to use with a default capping value of 16.
 # neutron_metadata_workers: 16
 
 ## Cap the maximun number of threads / workers when a user value is unspecified.
 neutron_api_threads_max: 16
+neutron_api_threads: "{{ [[ansible_processor_vcpus|default(2) // 2, 1] | max, neutron_api_threads_max] | min }}"
 
 neutron_metadata_backlog: 4096
 
@@ -534,8 +535,8 @@ neutron_dns_domain: openstacklocal
 neutron_dnsmasq_dns_servers: ""
 # Limit number of leases to prevent a denial-of-service.
 neutron_dnsmasq_lease_max: 16777216
-# If ``neutron_num_sync_threads`` is unset, the system will use the value of api_workers calculated
+# If ``neutron_num_sync_threads`` is unset, the system will use the value of
-# in templates/dhcp_agent.ini.j2 for num_sync_threads.
+# neutron_api_threads in templates/dhcp_agent.ini.j2 for num_sync_threads.
 # neutron_num_sync_threads: 4
 
 ## RPC

releasenotes/notes/capping_neutron_workers-d97a5d50ca996af5.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - Capping the default value for the variables ``neutron_api_workers``,
+    ``neutron_num_sync_threads`` and ``neutron_metadata_workers`` to 16 when
+    the user doesn't configure these variables. Default value is half the
+    number of vCPUs available on the machine with a capping value of 16.

templates/dhcp_agent.ini.j2

@@ -1,13 +1,10 @@
 # {{ ansible_managed }}
 
-{% set _api_threads = ansible_processor_vcpus|default(2) // 2 %}
-{% set api_threads = _api_threads if _api_threads > 0 else 1 %}
-
 # General
 [DEFAULT]
 debug = {{ debug }}
 
-num_sync_threads = {{ neutron_num_sync_threads | default(api_threads) }}
+num_sync_threads = {{ neutron_num_sync_threads | default(neutron_api_threads) }}
 
 # Drivers
 interface_driver = {{ neutron_plugins[neutron_plugin_type].driver_interface }}

templates/metadata_agent.ini.j2

@@ -1,8 +1,5 @@
 # {{ ansible_managed }}
 
-{% set _api_threads = ansible_processor_vcpus|default(2) // 2 %}
-{% set api_threads = _api_threads if _api_threads > 0 else 1 %}
-
 # General
 [DEFAULT]
 debug = {{ debug }}
@@ -27,7 +24,7 @@ nova_metadata_port = {{ nova_metadata_port }}
 metadata_proxy_shared_secret = {{ nova_metadata_proxy_secret }}
 
 # Workers and backlog requests
-metadata_workers = {{ neutron_metadata_workers | default(api_threads) }}
+metadata_workers = {{ neutron_metadata_workers | default(neutron_api_threads) }}
 metadata_backlog = {{ neutron_metadata_backlog }}
 
 # Caching

templates/neutron.conf.j2

@@ -1,8 +1,5 @@
 # {{ ansible_managed }}
 
-{% set _api_threads = [ansible_processor_vcpus|default(2) // 2, neutron_api_threads_max] | min %}
-{% set api_threads = _api_threads if _api_threads > 0 else 1 %}
-
 # General, applies to all host groups
 [DEFAULT]
 # Disable stderr logging
@@ -78,7 +75,7 @@ bind_port = 9696
 bind_host = 0.0.0.0
 
 # Workers
-api_workers = {{ neutron_api_workers | default(api_threads) }}
+api_workers = {{ neutron_api_workers | default(neutron_api_threads) }}
 rpc_workers = {{ neutron_rpc_workers }}
 
 {% set dhcp_agents_max = num_agent if num_agent > 2 else 2 %}