issue #317: ansible: fix log filtering in several cases

* mitogen/ansible_mitogen should only generate ERROR-level logs in
  log_path unless -vvv is enabled.
* Targets were accidentally configured to always have DEBUG set, causing
  many log messages to be sent on the wire even though they would be
  filtered in the master.

Closes #317.

ansible_mitogen/logging.py

@@ -85,8 +85,16 @@ def setup():
     mitogen.core.IOLOG.propagate = False
 
     if display.verbosity > 2:
-        logging.getLogger('ansible_mitogen').setLevel(logging.DEBUG)
         mitogen.core.LOG.setLevel(logging.DEBUG)
+        logging.getLogger('ansible_mitogen').setLevel(logging.DEBUG)
+    else:
+        # Mitogen copies the active log level into new children, allowing them
+        # to filter tiny messages before they hit the network, and therefore
+        # before they wake the IO loop. Explicitly setting INFO saves ~4%
+        # running against just the local machine.
+        mitogen.core.LOG.setLevel(logging.ERROR)
+        logging.getLogger('ansible_mitogen').setLevel(logging.ERROR)
 
     if display.verbosity > 3:
         mitogen.core.IOLOG.setLevel(logging.DEBUG)
+        logging.getLogger('ansible_mitogen').setLevel(logging.DEBUG)

ansible_mitogen/services.py

@@ -297,7 +297,8 @@ class ContextService(mitogen.service.Service):
                                 lambda: self._on_stream_disconnect(stream))
 
         self._send_module_forwards(context)
-        init_child_result = context.call(ansible_mitogen.target.init_child)
+        init_child_result = context.call(ansible_mitogen.target.init_child,
+                                         log_level=LOG.getEffectiveLevel())
 
         if os.environ.get('MITOGEN_DUMP_THREAD_STACKS'):
             from mitogen import debug

ansible_mitogen/target.py

@@ -202,7 +202,7 @@ def reset_temp_dir(econtext):
 
 
 @mitogen.core.takes_econtext
-def init_child(econtext):
+def init_child(econtext, log_level):
     """
     Called by ContextService immediately after connection; arranges for the
     (presently) spotless Python interpreter to be forked, where the newly
@@ -213,6 +213,9 @@ def init_child(econtext):
     polluting the global interpreter state in a way that effects explicitly
     isolated modules.
 
+    :param int log_level:
+        Logging package level active in the master.
+
     :returns:
         Dict like::
 
@@ -230,6 +233,12 @@ def init_child(econtext):
     _fork_parent = econtext.router.fork()
     reset_temp_dir(econtext)
 
+    # Copying the master's log level causes log messages to be filtered before
+    # they reach LogForwarder, thus reducing an influx of tiny messges waking
+    # the connection multiplexer process in the master.
+    LOG.setLevel(log_level)
+    logging.getLogger('ansible_mitogen').setLevel(log_level)
+
     return {
         'fork_context': _fork_parent,
         'home_dir': mitogen.core.to_text(os.path.expanduser('~')),