Allow configuration of CPU affinity

Make it possible to set the CPU affinity in the config file, so that we don't
need to remember to do it manually every time.

synapse/app/_base.py

@@ -15,6 +15,7 @@
 import gc
 import logging
 
+import affinity
 from daemonize import Daemonize
 from synapse.util import PreserveLoggingContext
 from synapse.util.rlimit import change_resource_limit
@@ -40,7 +41,8 @@ def start_worker_reactor(appname, config):
         config.gc_thresholds,
         config.worker_pid_file,
         config.worker_daemonize,
-        logger
+        config.worker_cpu_affinity,
+        logger,
     )
 
 
@@ -50,6 +52,7 @@ def start_reactor(
         gc_thresholds,
         pid_file,
         daemonize,
+        cpu_affinity,
         logger,
 ):
     """ Run the reactor in the main process
@@ -63,6 +66,7 @@ def start_reactor(
         gc_thresholds:
         pid_file (str): name of pid file to write to if daemonize is True
         daemonize (bool): true to run the reactor in a background process
+        cpu_affinity (int|None): cpu affinity mask
         logger (logging.Logger): logger instance to pass to Daemonize
     """
 
@@ -73,6 +77,9 @@ def start_reactor(
         # between the sentinel and `run` logcontexts.
         with PreserveLoggingContext():
             logger.info("Running")
+            if cpu_affinity is not None:
+                logger.info("Setting CPU affinity to %s" % cpu_affinity)
+                affinity.set_process_affinity_mask(0, cpu_affinity)
             change_resource_limit(soft_file_limit)
             if gc_thresholds:
                 gc.set_threshold(*gc_thresholds)

synapse/app/homeserver.py

@@ -442,6 +442,7 @@ def run(hs):
         hs.config.gc_thresholds,
         hs.config.pid_file,
         hs.config.daemonize,
+        hs.config.cpu_affinity,
         logger,
     )
 

synapse/config/server.py

@@ -29,6 +29,7 @@ class ServerConfig(Config):
         self.user_agent_suffix = config.get("user_agent_suffix")
         self.use_frozen_dicts = config.get("use_frozen_dicts", False)
         self.public_baseurl = config.get("public_baseurl")
+        self.cpu_affinity = config.get("cpu_affinity")
 
         # Whether to send federation traffic out in this process. This only
         # applies to some federation traffic, and so shouldn't be used to
@@ -147,6 +148,17 @@ class ServerConfig(Config):
         # When running as a daemon, the file to store the pid in
         pid_file: %(pid_file)s
 
+        # CPU affinity mask. Setting this restricts the CPUs on which the process
+        # will be scheduled. It is represented as a bitmask, with the lowest order
+        # bit corresponding to the first logical CPU and the highest order bit
+        # corresponding to the last logical CPU. Not all CPUs may exist on a
+        # given system but a mask may specify more CPUs than are present.
+        # For example:
+        #    0x00000001  is processor #0,
+        #    0x00000003  is processors #0 and #1,
+        #    0xFFFFFFFF  is all processors (#0 through #31).
+        # cpu_affinity: 0xFFFFFFFF
+
         # Whether to serve a web client from the HTTP/HTTPS root resource.
         web_client: True
 

synapse/config/workers.py

@@ -33,6 +33,7 @@ class WorkerConfig(Config):
         self.worker_name = config.get("worker_name", self.worker_app)
 
         self.worker_main_http_uri = config.get("worker_main_http_uri", None)
+        self.worker_cpu_affinity = config.get("worker_cpu_affinity")
 
         if self.worker_listeners:
             for listener in self.worker_listeners:

synapse/python_dependencies.py

@@ -40,6 +40,7 @@ REQUIREMENTS = {
     "pymacaroons-pynacl": ["pymacaroons"],
     "msgpack-python>=0.3.0": ["msgpack"],
     "phonenumbers>=8.2.0": ["phonenumbers"],
+    "affinity": ["affinity"],
 }
 CONDITIONAL_REQUIREMENTS = {
     "web_client": {