Added some comments and a warning message to pyauto perf tests in perf.py.

chrome/test/functional/perf.py

 #!/usr/bin/python
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Basic pyauto performance tests.
 
 For tests that need to be run for multiple iterations (e.g., so that average
 and standard deviation values can be reported), the default number of iterations
 run for each of these tests is specified by |_DEFAULT_NUM_ITERATIONS|.
@@ skipping 94 matching lines @@
     if values:
       avg = float(sum(values)) / len(values)
       if len(values) > 1:
         temp_vals = [math.pow(x - avg, 2) for x in values]
         std_dev = math.sqrt(sum(temp_vals) / (len(temp_vals) - 1))
     return avg, std_dev
 
   def _OutputPerfGraphValue(self, description, value):
     """Outputs a performance value to have it graphed on the performance bots.
 
-    Only used for ChromeOS.
+    Only used for ChromeOS.  The performance bots have a 30-character limit on
+    the length of the description for a performance value.  Any characters
+    beyond that are truncated before results are stored in the autotest
+    database.
 
     Args:
-      description: A string description of the performance value.
+      description: A string description of the performance value.  This will
+                   be truncated to 30 characters when stored in the autotest
+                   database.
       value: A numeric value representing a single performance measurement.
     """
     if self.IsChromeOS():
+      if len(description) > 30:
+        logging.warning('The description "%s" will be truncated to "%s" '
+                        '(length 30) when added to the autotest database.' %

[truty, 2011/10/20 00:12:01]

Not a big deal, but I think it's preferred when calling logging.xxxx() to avoid
the % string substitution and simple append arguments i.e. logging.warning('blah
%s more %s.', sub1, sub2)

[dennis_jeffrey, 2011/10/20 01:18:21]

Done (also changed in several other places in this file where the same comment
applies).

+                        (description, description[:30]))
       print '\n%s(\'%s\', %.2f)%s' % (self._PERF_OUTPUT_MARKER_PRE, description,
                                       value, self._PERF_OUTPUT_MARKER_POST)
 
   def _PrintSummaryResults(self, description, values, units):
     """Logs summary measurement information.
 
+    This function computes and outputs the average and standard deviation of
+    the specified list of value measurements.  It also invokes
+    _OutputPerfGraphValue() with the computed *average* value, to ensure the
+    average value can be plotted in a performance graph.
+
     Args:
       description: A string description for the specified results.
       values: A list of numeric value measurements.
       units: A string specifying the units for the specified measurements.
     """
     logging.info('Results for: ' + description)
     if values:
       avg, std_dev = self._AvgAndStdDev(values)
       logging.info('Number of iterations: %d', len(values))
       for val in values:
@@ skipping 739 matching lines @@
     """Identifies the port number to which the server is currently bound.
 
     Returns:
       The numeric port number to which the server is currently bound.
     """
     return self._server.server_address[1]
 
 
 if __name__ == '__main__':
   pyauto_functional.Main()