telemtry: better error message for not enought frames cases.

R=tonyg@chromium.org
BUG=360204

Review URL: https://codereview.chromium.org/255603003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266281 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf/metrics/rendering_stats.py

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 from operator import attrgetter
+from telemetry.page import page_measurement
 
 # These are LatencyInfo component names indicating the various components
 # that the input event has travelled through.
@@ -16,6 +17,19 @@ BEGIN_COMP_NAME = 'INPUT_EVENT_LATENCY_BEGIN_RWH_COMPONENT'
 END_COMP_NAME = 'INPUT_EVENT_LATENCY_TERMINATED_FRAME_SWAP_COMPONENT'
 
 
+class NotEnoughFramesError(page_measurement.MeasurementFailure):
+  def __init__(self, frame_count):
+    super(NotEnoughFramesError, self).__init__(
+      'Only %i frame timestamps were collected ' % frame_count +
+      '(at least two are required).\n'
+      'Issues that have caused this in the past:\n' +
+      '- Browser bugs that prevents the page from redrawing\n' +
+      '- Bugs in the synthetic gesture code\n' +
+      '- Page and benchmark out of sync (e.g. clicked element was renamed)\n' +
+      '- Pages that render extremely slow\n' +
+      '- Pages that can\'t be scrolled')
+
+
 def GetScrollInputLatencyEvents(scroll_type, browser_process, timeline_range):
   """Get scroll events' LatencyInfo from the browser process's trace buffer
      that are within the timeline_range.
@@ -160,6 +174,12 @@ class RenderingStats(object):
       self.initImplThreadStatsFromTimeline(timeline_range)
       self.initScrollLatencyStatsFromTimeline(browser_process, timeline_range)
 
+    # Check if we have collected at least 2 frames in every range. Otherwise we
+    # can't compute any meaningful metrics.
+    for segment in self.frame_timestamps:
+      if len(segment) < 2:
+        raise NotEnoughFramesError(len(segment))
+
   def initScrollLatencyStatsFromTimeline(self, browser_process, timeline_range):
     mouse_wheel_events = GetScrollInputLatencyEvents(
         "MouseWheel", browser_process, timeline_range)

tools/perf/metrics/rendering_stats_unittest.py

@@ -11,6 +11,7 @@ from metrics.rendering_stats import ComputeMouseWheelScrollLatency
 from metrics.rendering_stats import ComputeTouchScrollLatency
 from metrics.rendering_stats import HasRenderingStats
 from metrics.rendering_stats import RenderingStats
+from metrics.rendering_stats import NotEnoughFramesError
 import telemetry.core.timeline.bounds as timeline_bounds
 from telemetry.core.timeline import model
 import telemetry.core.timeline.async_slice as tracing_async_slice
@@ -224,6 +225,46 @@ class RenderingStatsUnitTest(unittest.TestCase):
     process_with_frames.FinalizeImport()
     self.assertTrue(HasRenderingStats(thread_with_frames))
 
+  def testRangeWithoutFrames(self):
+    timer = MockTimer()
+    timeline = model.TimelineModel()
+
+    # Create a renderer process, with a main thread and impl thread.
+    renderer = timeline.GetOrCreateProcess(pid = 2)
+    renderer_main = renderer.GetOrCreateThread(tid = 21)
+    renderer_compositor = renderer.GetOrCreateThread(tid = 22)
+
+    # Create 10 main and impl rendering stats events for Action A.
+    timer.Advance(2, 4)
+    renderer_main.BeginSlice('webkit.console', 'ActionA', timer.Get(), '')
+    for i in xrange(0, 10):
+      first = (i == 0)
+      AddMainThreadRenderingStats(timer, renderer_main, first, None)
+      AddImplThreadRenderingStats(timer, renderer_compositor, first, None)
+    timer.Advance(2, 4)
+    renderer_main.EndSlice(timer.Get())
+
+    # Create 5 main and impl rendering stats events not within any action.
+    for i in xrange(0, 5):
+      first = (i == 0)
+      AddMainThreadRenderingStats(timer, renderer_main, first, None)
+      AddImplThreadRenderingStats(timer, renderer_compositor, first, None)
+
+    # Create Action B without any frames. This should trigger
+    # NotEnoughFramesError when the RenderingStats object is created.
+    timer.Advance(2, 4)
+    renderer_main.BeginSlice('webkit.console', 'ActionB', timer.Get(), '')
+    timer.Advance(2, 4)
+    renderer_main.EndSlice(timer.Get())
+
+    renderer.FinalizeImport()
+
+    timeline_markers = timeline.FindTimelineMarkers(['ActionA', 'ActionB'])
+    timeline_ranges = [ timeline_bounds.Bounds.CreateFromEvent(marker)
+                        for marker in timeline_markers ]
+    self.assertRaises(NotEnoughFramesError, RenderingStats,
+                      renderer, None, timeline_ranges)
+
   def testFromTimeline(self):
     timeline = model.TimelineModel()