[Telemetry] Have powermetrics summarize power usage rather than doing it by ourselves

Tell `powermetrics` to print a summary instead of telling it to sample and summing ourselves.

Aim is to try to get more accurate measurements.

BUG=None

Review URL: https://codereview.chromium.org/330543008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276881 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/platform/power_monitor/powermetrics_power_monitor.py

@@ -7,7 +7,6 @@ import logging
 import os
 import plistlib
 import shutil
-import signal
 import tempfile
 import xml.parsers.expat
 
@@ -42,7 +41,9 @@ class PowerMetricsPowerMonitor(power_monitor.PowerMonitor):
     self._output_filename = os.path.join(self._output_directory,
         'powermetrics.output')
     args = ['-f', 'plist',
-            '-u', self._output_filename]
+            '-u', self._output_filename,
+            '-i0',
+            '--show-usage-summary']
     self._powermetrics_process = self._backend.LaunchApplication(
         self.binary_path, args, elevate_privilege=True)
 
@@ -130,6 +131,7 @@ class PowerMetricsPowerMonitor(power_monitor.PowerMonitor):
     # powermetrics outputs multiple plists separated by null terminators.
     raw_plists = powermetrics_output.split('\0')
     raw_plists = [x for x in raw_plists if len(x) > 0]
+    assert(len(raw_plists) == 1)
 
     # -------- Examine contents of first plist for systems specs. --------
     plist = PowerMetricsPowerMonitor._ParsePlistString(raw_plists[0])
@@ -171,17 +173,18 @@ class PowerMetricsPowerMonitor(power_monitor.PowerMonitor):
           cpu_num += 1
 
     # -------- Parse Data Out of Plists --------
-    for raw_plist in raw_plists:
-      plist = PowerMetricsPowerMonitor._ParsePlistString(raw_plist)
+    plist = PowerMetricsPowerMonitor._ParsePlistString(raw_plists[0])
     if not plist:
-        continue
+      logging.error("Error parsing plist.")
+      return
 
     # Duration of this sample.
     sample_duration_ms = int(plist['elapsed_ns']) / 10**6
     sample_durations.append(sample_duration_ms)
 
     if 'processor' not in plist:
-        continue
+      logging.error("'processor' field not found in plist.")
+      return
     processor = plist['processor']
 
     energy_consumption_mw = int(processor.get('package_watts', 0)) * 10**3
@@ -238,8 +241,7 @@ class PowerMetricsPowerMonitor(power_monitor.PowerMonitor):
         "StartMonitoringPower() not called.")
     # Tell powermetrics to take an immediate sample.
     try:
-      self._powermetrics_process.send_signal(signal.SIGINFO)
-      self._powermetrics_process.send_signal(signal.SIGTERM)
+      self._powermetrics_process.terminate()
       (power_stdout, power_stderr) = self._powermetrics_process.communicate()
       returncode = self._powermetrics_process.returncode
       assert returncode in [0, -15], (