[Telemetry] Fix idle wakeup reporting in the face of dead processes

tools/perf/metrics/power.py

 # Copyright 2014 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.
 
 import time
 
 from metrics import Metric
+from telemetry.core.platform import timeline_objects
 from telemetry.value import scalar
 
 
 class PowerMetric(Metric):
   """A metric for measuring power usage."""
 
   # System power draw while idle.
   _quiescent_power_draw_mwh = 0
 
   def __init__(self, browser, quiescent_measurement_time_s=0):
@@ skipping 133 matching lines @@
     # Add CPU c-state residency measurements.
     cstate_percent = whole_package_utilization.get('cstate_residency_percent')
     if cstate_percent is not None:
       for state, percent in cstate_percent.iteritems():
         results.AddValue(scalar.ScalarValue(
             results.current_page, 'cpu_cstate_%s_residency_percent' % state,
             '%', percent, important=False))
 
     self._results = None
 
 def _SubtractCpuStats(cpu_stats, start_cpu_stats):

[tonyg, 2014/08/24 16:53:43]

I was hoping this whole method would go away from this file in favor of an
inlined subtraction. Is that feasible?

   """Computes number of idle wakeups that occurred over measurement period.
 
   Each of the two cpu_stats arguments is a dict as returned by the
   Browser.cpu_stats call.
 
   Returns:
     A dict of process type names (Browser, Renderer, etc.) to idle wakeup count
     over the period recorded by the input.
   """
   cpu_delta = {}
   for process_type in cpu_stats:
     assert process_type in start_cpu_stats, 'Mismatching process types'
     # Skip any process_types that are empty.
     if (not cpu_stats[process_type]) or (not start_cpu_stats[process_type]):
       continue
     # Skip if IdleWakeupCount is not present.
     if (('IdleWakeupCount' not in cpu_stats[process_type]) or
         ('IdleWakeupCount' not in start_cpu_stats[process_type])):
       continue
+
+    # Verify that the IdleWakeupCount field has been converted to a

[tonyg, 2014/08/24 16:53:43]

Let's just kill this comment. It answers "what" instead of "why" which is
usually extraneous.

[jeremy, 2014/08/26 14:14:16]

Done.

+    # TimlineData-based object.
+    assert isinstance(cpu_stats[process_type]['IdleWakeupCount'],
+        timeline_objects.IdleStatsData)
     idle_wakeup_delta = (cpu_stats[process_type]['IdleWakeupCount'] -
                         start_cpu_stats[process_type]['IdleWakeupCount'])
-    cpu_delta[process_type] = idle_wakeup_delta
+    cpu_delta[process_type] = idle_wakeup_delta.IdleWakeupCount()
   return cpu_delta