tools/perf/perf_tools/histogram.py

   1 # Copyright (c) 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 import json
   5 import logging
   6
   7 def SubtractHistogram(histogram_json, start_histogram_json):
   8   """Subtracts a previous histogram from a histogram. Both parameters are json
   9   serializations of histograms."""
  10   start_histogram = json.loads(start_histogram_json)
  11   # It's ok if the start histogram is empty (we had no data, maybe even no
  12   # histogram at all, at the start of the test).
  13   if 'buckets' not in start_histogram:
  14     return histogram_json
  15
  16   histogram = json.loads(histogram_json)
  17   if ('pid' in start_histogram and 'pid' in histogram
  18       and start_histogram['pid'] != histogram['pid']):
  19     raise Exception(
  20         'Trying to compare histograms from different processes (%d and %d)'
  21         % (start_histogram['pid'], histogram['pid']))
  22
  23   start_histogram_buckets = dict()
  24   for b in start_histogram['buckets']:
  25     start_histogram_buckets[b['low']] = b['count']
  26
  27   new_buckets = []
  28   for b in histogram['buckets']:
  29     new_bucket = b
  30     low = b['low']
  31     if low in start_histogram_buckets:
  32       new_bucket['count'] = b['count'] - start_histogram_buckets[low]
  33       if new_bucket['count'] < 0:
  34         logging.error('Histogram subtraction error, starting histogram most '
  35                       'probably invalid.')
  36     if new_bucket['count']:
  37       new_buckets.append(new_bucket)
  38   histogram['buckets'] = new_buckets
  39   histogram['count'] -= start_histogram['count']
  40
  41   return json.dumps(histogram)