UMA metric for LayerUpdateTimes

cc/trees/layer_tree_host_in_process.cc

Index: cc/trees/layer_tree_host_in_process.cc
diff --git a/cc/trees/layer_tree_host_in_process.cc b/cc/trees/layer_tree_host_in_process.cc
index 8a9d969f3a6e84dd2ccfa29311a4a836ea8cfa63..58c78f85eb05c72004ad6e85e68ba85c01829a4a 100644
--- a/cc/trees/layer_tree_host_in_process.cc
+++ b/cc/trees/layer_tree_host_in_process.cc
@@ -23,7 +23,9 @@
 #include "base/single_thread_task_runner.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
+#include "base/timer/elapsed_timer.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/base/math_util.h"
@@ -582,12 +584,39 @@ void LayerTreeHostInProcess::Composite(base::TimeTicks frame_begin_time) {
   proxy->CompositeImmediately(frame_begin_time);
 }
 
+static int GetLayersUpdateTimeHistogramBucket(size_t numLayers) {
+  // We uses the following exponential (ratio 2) bucketization:
+  // [0, 10), [10, 30), [30, 70), [70, 150), [150, infinity)
+  if (numLayers < 10)
+    return 0;
+  else if (numLayers >= 10 && numLayers < 30)
+    return 1;
+  else if (numLayers >= 30 && numLayers < 70)
+    return 2;
+  else if (numLayers >= 70 && numLayers < 150)
+    return 3;
+  else
+    return 4;
+}
+
 bool LayerTreeHostInProcess::UpdateLayers() {
   if (!layer_tree_->root_layer())
     return false;
   DCHECK(!layer_tree_->root_layer()->parent());
+  base::ElapsedTimer timer;
+
   bool result = DoUpdateLayers(layer_tree_->root_layer());
   micro_benchmark_controller_.DidUpdateLayers();
+
+  std::string histogram_name = base::StringPrintf(
+      "Compositing.Renderer.LayersUpdateTime.%d",

[ajuma, 2016/12/03 01:28:23]

This is going to get called for both the browser and renderers. To separate
them, you can use GetClientNameForMetrics (see LayerTreeHostImpl::PrepareToDraw
for an example).

[majidvp, 2016/12/08 20:19:18]

Thanks for the comment. Fixed!

+      GetLayersUpdateTimeHistogramBucket(layer_tree_->NumLayers()));
+  base::Histogram::FactoryTimeGet(
+      histogram_name, base::TimeDelta::FromMilliseconds(1),
+      base::TimeDelta::FromSeconds(10), 50,
+      base::HistogramBase::kUmaTargetedHistogramFlag)
+      ->AddTime(timer.Elapsed());
+
   return result || next_commit_forces_redraw_;
 }