tools/perf/metrics/speedindex.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 from telemetry.util import image_util
   6 from telemetry.util import rgba_color
   7 from telemetry.value import scalar
   8
   9 from metrics import Metric
  10
  11
  12 class SpeedIndexMetric(Metric):
  13   """The speed index metric is one way of measuring page load speed.
  14
  15   It is meant to approximate user perception of page load speed, and it
  16   is based on the amount of time that it takes to paint to the visual
  17   portion of the screen. It includes paint events that occur after the
  18   onload event, and it doesn't include time loading things off-screen.
  19
  20   This speed index metric is based on WebPageTest.org (WPT).
  21   For more info see: http://goo.gl/e7AH5l
  22   """
  23   def __init__(self):
  24     super(SpeedIndexMetric, self).__init__()
  25     self._impl = None
  26
  27   @classmethod
  28   def CustomizeBrowserOptions(cls, options):
  29     options.AppendExtraBrowserArgs('--disable-infobars')
  30
  31   def Start(self, _, tab):
  32     """Start recording events.
  33
  34     This method should be called in the WillNavigateToPage method of
  35     a PageTest, so that all the events can be captured. If it's called
  36     in DidNavigateToPage, that will be too late.
  37     """
  38     if not tab.video_capture_supported:
  39       return
  40     self._impl = VideoSpeedIndexImpl()
  41     self._impl.Start(tab)
  42
  43   def Stop(self, _, tab):
  44     """Stop recording."""
  45     if not tab.video_capture_supported:
  46       return
  47     assert self._impl, 'Must call Start() before Stop()'
  48     assert self.IsFinished(tab), 'Must wait for IsFinished() before Stop()'
  49     self._impl.Stop(tab)
  50
  51   # Optional argument chart_name is not in base class Metric.
  52   # pylint: disable=W0221
  53   def AddResults(self, tab, results, chart_name=None):
  54     """Calculate the speed index and add it to the results."""
  55     try:
  56       if tab.video_capture_supported:
  57         index = self._impl.CalculateSpeedIndex(tab)
  58         none_value_reason = None
  59       else:
  60         index = None
  61         none_value_reason = 'Video capture is not supported.'
  62     finally:
  63       self._impl = None  # Release the tab so that it can be disconnected.
  64
  65     results.AddValue(scalar.ScalarValue(
  66         results.current_page, '%s_speed_index' % chart_name, 'ms', index,
  67         description='Speed Index. This focuses on time when visible parts of '
  68                     'page are displayed and shows the time when the '
  69                     'first look is "almost" composed. If the contents of the '
  70                     'testing page are composed by only static resources, load '
  71                     'time can measure more accurately and speed index will be '
  72                     'smaller than the load time. On the other hand, If the '
  73                     'contents are composed by many XHR requests with small '
  74                     'main resource and javascript, speed index will be able to '
  75                     'get the features of performance more accurately than load '
  76                     'time because the load time will measure the time when '
  77                     'static resources are loaded. If you want to get more '
  78                     'detail, please refer to http://goo.gl/Rw3d5d. Currently '
  79                     'there are two implementations: for Android and for '
  80                     'Desktop. The Android version uses video capture; the '
  81                     'Desktop one uses paint events and has extra overhead to '
  82                     'catch paint events.', none_value_reason=none_value_reason))
  83
  84   def IsFinished(self, tab):
  85     """Decide whether the recording should be stopped.
  86
  87     A page may repeatedly request resources in an infinite loop; a timeout
  88     should be placed in any measurement that uses this metric, e.g.:
  89       def IsDone():
  90         return self._speedindex.IsFinished(tab)
  91       util.WaitFor(IsDone, 60)
  92
  93     Returns:
  94       True if 2 seconds have passed since last resource received, false
  95       otherwise.
  96     """
  97     return tab.HasReachedQuiescence()
  98
  99
 100 class SpeedIndexImpl(object):
 101
 102   def Start(self, tab):
 103     raise NotImplementedError()
 104
 105   def Stop(self, tab):
 106     raise NotImplementedError()
 107
 108   def GetTimeCompletenessList(self, tab):
 109     """Returns a list of time to visual completeness tuples.
 110
 111     In the WPT PHP implementation, this is also called 'visual progress'.
 112     """
 113     raise NotImplementedError()
 114
 115   def CalculateSpeedIndex(self, tab):
 116     """Calculate the speed index.
 117
 118     The speed index number conceptually represents the number of milliseconds
 119     that the page was "visually incomplete". If the page were 0% complete for
 120     1000 ms, then the score would be 1000; if it were 0% complete for 100 ms
 121     then 90% complete (ie 10% incomplete) for 900 ms, then the score would be
 122     1.0*100 + 0.1*900 = 190.
 123
 124     Returns:
 125       A single number, milliseconds of visual incompleteness.
 126     """
 127     time_completeness_list = self.GetTimeCompletenessList(tab)
 128     prev_completeness = 0.0
 129     speed_index = 0.0
 130     prev_time = time_completeness_list[0][0]
 131     for time, completeness in time_completeness_list:
 132       # Add the incemental value for the interval just before this event.
 133       elapsed_time = time - prev_time
 134       incompleteness = (1.0 - prev_completeness)
 135       speed_index += elapsed_time * incompleteness
 136
 137       # Update variables for next iteration.
 138       prev_completeness = completeness
 139       prev_time = time
 140     return int(speed_index)
 141
 142
 143 class VideoSpeedIndexImpl(SpeedIndexImpl):
 144
 145   def __init__(self, image_util_module=image_util):
 146     # Allow image_util to be passed in so we can fake it out for testing.
 147     super(VideoSpeedIndexImpl, self).__init__()
 148     self._time_completeness_list = None
 149     self._image_util_module = image_util_module
 150
 151   def Start(self, tab):
 152     assert tab.video_capture_supported
 153     # Blank out the current page so it doesn't count towards the new page's
 154     # completeness.
 155     tab.Highlight(rgba_color.WHITE)
 156     # TODO(tonyg): Bitrate is arbitrary here. Experiment with screen capture
 157     # overhead vs. speed index accuracy and set the bitrate appropriately.
 158     tab.StartVideoCapture(min_bitrate_mbps=4)
 159
 160   def Stop(self, tab):
 161     # Ignore white because Chrome may blank out the page during load and we want
 162     # that to count as 0% complete. Relying on this fact, we also blank out the
 163     # previous page to white. The tolerance of 8 experimentally does well with
 164     # video capture at 4mbps. We should keep this as low as possible with
 165     # supported video compression settings.
 166     video_capture = tab.StopVideoCapture()
 167     histograms = [(time, self._image_util_module.GetColorHistogram(
 168                        image, ignore_color=rgba_color.WHITE, tolerance=8))
 169                   for time, image in video_capture.GetVideoFrameIter()]
 170
 171     start_histogram = histograms[0][1]
 172     final_histogram = histograms[-1][1]
 173     total_distance = start_histogram.Distance(final_histogram)
 174
 175     def FrameProgress(histogram):
 176       if total_distance == 0:
 177         if histogram.Distance(final_histogram) == 0:
 178           return 1.0
 179         else:
 180           return 0.0
 181       return 1 - histogram.Distance(final_histogram) / total_distance
 182
 183     self._time_completeness_list = [(time, FrameProgress(hist))
 184                                     for time, hist in histograms]
 185
 186   def GetTimeCompletenessList(self, tab):
 187     assert self._time_completeness_list, 'Must call Stop() first.'
 188     return self._time_completeness_list