tools/perf/metrics/histogram_util.py

   1 # Copyright 2013 The Chromium Authors. All rights reserved.
   2 # Use of this source code is governed by a BSD-style license that can be
   3 # found in the LICENSE file.
   4
   5 """This is a helper module to get and manipulate histogram data.
   6
   7 The histogram data is the same data as is visible from "chrome://histograms".
   8 More information can be found at: chromium/src/base/metrics/histogram.h
   9 """
  10
  11 import json
  12 import logging
  13
  14 BROWSER_HISTOGRAM = 'browser_histogram'
  15 RENDERER_HISTOGRAM = 'renderer_histogram'
  16
  17
  18 def CustomizeBrowserOptions(options):
  19   """Allows histogram collection."""
  20   options.AppendExtraBrowserArgs(['--enable-stats-collection-bindings'])
  21
  22
  23 def SubtractHistogram(histogram_json, start_histogram_json):
  24   """Subtracts a previous histogram from a histogram.
  25
  26   Both parameters and the returned result are json serializations.
  27   """
  28   start_histogram = json.loads(start_histogram_json)
  29   # It's ok if the start histogram is empty (we had no data, maybe even no
  30   # histogram at all, at the start of the test).
  31   if 'buckets' not in start_histogram:
  32     return histogram_json
  33
  34   histogram = json.loads(histogram_json)
  35   if ('pid' in start_histogram and 'pid' in histogram
  36       and start_histogram['pid'] != histogram['pid']):
  37     raise Exception(
  38         'Trying to compare histograms from different processes (%d and %d)'
  39         % (start_histogram['pid'], histogram['pid']))
  40
  41   start_histogram_buckets = dict()
  42   for b in start_histogram['buckets']:
  43     start_histogram_buckets[b['low']] = b['count']
  44
  45   new_buckets = []
  46   for b in histogram['buckets']:
  47     new_bucket = b
  48     low = b['low']
  49     if low in start_histogram_buckets:
  50       new_bucket['count'] = b['count'] - start_histogram_buckets[low]
  51       if new_bucket['count'] < 0:
  52         logging.error('Histogram subtraction error, starting histogram most '
  53                       'probably invalid.')
  54     if new_bucket['count']:
  55       new_buckets.append(new_bucket)
  56   histogram['buckets'] = new_buckets
  57   histogram['count'] -= start_histogram['count']
  58
  59   return json.dumps(histogram)
  60
  61
  62 def GetHistogram(histogram_type, histogram_name, tab):
  63   """Get a json serialization of a histogram."""
  64   assert histogram_type in [BROWSER_HISTOGRAM, RENDERER_HISTOGRAM]
  65   function = 'getHistogram'
  66   if histogram_type == BROWSER_HISTOGRAM:
  67     function = 'getBrowserHistogram'
  68   histogram_json = tab.EvaluateJavaScript(
  69       'statsCollectionController.%s("%s")' %
  70       (function, histogram_name))
  71   if histogram_json:
  72     return histogram_json
  73   return None
  74
  75
  76 def GetHistogramCount(histogram_type, histogram_name, tab):
  77   """Get the count of events for the given histograms."""
  78   histogram_json = GetHistogram(histogram_type, histogram_name, tab)
  79   histogram = json.loads(histogram_json)
  80   if 'count' in histogram:
  81     return histogram['count']
  82   else:
  83     return 0
  84
  85 def GetHistogramSum(histogram_type, histogram_name, tab):
  86   """Get the sum of events for the given histograms."""
  87   histogram_json = GetHistogram(histogram_type, histogram_name, tab)
  88   histogram = json.loads(histogram_json)
  89   if 'sum' in histogram:
  90     return histogram['sum']
  91   else:
  92     return 0