Telemetry: adds CPU frequency stats.

tools/perf/metrics/cpu.py

Index: tools/perf/metrics/cpu.py
diff --git a/tools/perf/metrics/cpu.py b/tools/perf/metrics/cpu.py
index aa57b073078a791ea945e954f030c1c3cf9b3d9a..1c5979764b6d8d9e720bda1ca0ed8e312e935cb0 100644
--- a/tools/perf/metrics/cpu.py
+++ b/tools/perf/metrics/cpu.py
@@ -30,10 +30,24 @@ class CpuMetric(Metric):
     assert self._results, 'Must call Stop() first'
     # Add a result for each process type.
     for process_type in self._results:
+      if process_type == 'Global':
+        continue
       trace_name_for_process = '%s_%s' % (trace_name, process_type.lower())
       cpu_percent = 100 * self._results[process_type]
       results.Add(trace_name_for_process, '%', cpu_percent,
                   chart_name='cpu_utilization', data_type='unimportant')
+    # Add a result for Global CPU stats: these are system-wide metrics,
+    # not per process as the ones above.
+    total_time = 0.0
+    frequency_sum = 0.0
+    for frequency, time_in_state in \
+        self._results['Global']['GlobalCpuFrequencyStats'].iteritems():
+      frequency_sum += (frequency * time_in_state)
+      total_time += time_in_state
+    results.Add('average_frequency_hz', 'Hz',

[qyearsley, 2014/04/22 18:22:26]

This would require changing a couple places, but might it be reasonable to use
MHz or GHz as the units and report a floating-point number?

(It's easier to see the difference between 200 and 2000 MHz than it is to see
between 200000000 and 2000000000 Hz...)

[bulach, 2014/04/22 18:34:50]

good point! rounded to MHz with 2 digits precision, hopefully that's good
enough?

[qyearsley, 2014/04/22 18:48:37]

I think that sounds good; although note that in order for the perf dashboard to
know whether increase/decrease should be considered a regression, you would have
to add an entry to src/tools/perf/unit-info.json.

But, in this case, is higher or lower necessarily better? Lower means less power
consumption, but possibly slower page load right?

+                int(frequency_sum / total_time),

[qyearsley, 2014/04/22 18:22:26]

Is total_time ever 0.0? (i.e. would it ever be the case that
self._results['Global']['GlobalCpuFrequencyStats'] is empty, or contains an
entry with a time_in_state of 0.0)?

For the other CPU stats, we're expecting that it if everything is working OK,
then time should never be 0, and we have:
  assert total_time > 0, 'Expected total_time > 0, was: %d' % total_time

[bulach, 2014/04/22 18:34:50]

ahn, great catch, thanks! I'm only adding this to "proc_supporting" platforms,
so no Windows for now..
guarded with an if instead of an assert.

+                chart_name='cpu_frequency',
+                data_type='unimportant')
 
 
 def _SubtractCpuStats(cpu_stats, start_cpu_stats):
@@ -56,7 +70,9 @@ def _SubtractCpuStats(cpu_stats, start_cpu_stats):
   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]):
+    if ((not cpu_stats[process_type]) or
+        (not start_cpu_stats[process_type]) or
+        process_type == 'Global'):
       continue
     cpu_process_time = (cpu_stats[process_type]['CpuProcessTime'] -
                         start_cpu_stats[process_type]['CpuProcessTime'])
@@ -64,5 +80,16 @@ def _SubtractCpuStats(cpu_stats, start_cpu_stats):
                   start_cpu_stats[process_type]['TotalTime'])
     assert total_time > 0, 'Expected total_time > 0, was: %d' % total_time
     cpu_usage[process_type] = float(cpu_process_time) / total_time
-  return cpu_usage
 
+  if 'Global' not in cpu_stats:
+    return cpu_usage
+
+  frequency_stats = cpu_stats['Global']['GlobalCpuFrequencyStats']
+  start_frequency_stats = start_cpu_stats['Global']['GlobalCpuFrequencyStats']
+  total_frequency_stats = {}
+  for k in frequency_stats.iterkeys():
+    total_frequency_stats[k] = frequency_stats[k] - start_frequency_stats[k]
+
+  cpu_usage['Global'] = {}
+  cpu_usage['Global']['GlobalCpuFrequencyStats'] = total_frequency_stats
+  return cpu_usage