Break down end-to-end scroll update latency UMA metrics

content/browser/renderer_host/render_widget_host_latency_tracker.cc

Index: content/browser/renderer_host/render_widget_host_latency_tracker.cc
diff --git a/content/browser/renderer_host/render_widget_host_latency_tracker.cc b/content/browser/renderer_host/render_widget_host_latency_tracker.cc
index 2d738c491910c4d429709da26d4ecd6193f9105b..d248648e2ecda151ffd39ef224945eff2c5123ed 100644
--- a/content/browser/renderer_host/render_widget_host_latency_tracker.cc
+++ b/content/browser/renderer_host/render_widget_host_latency_tracker.cc
@@ -171,6 +171,69 @@ void ComputeScrollLatencyHistograms(
             .InMicroseconds(),
         1, 1000000, 100);
   }
+
+  LatencyInfo::LatencyComponent rendering_scheduled_component;
+  bool rendering_scheduled_on_main = latency.FindLatency(
+      ui::INPUT_EVENT_LATENCY_RENDERING_SCHEDULED_MAIN_COMPONENT,
+      0, &rendering_scheduled_component);
+
+  if (!rendering_scheduled_on_main) {
+    if (!latency.FindLatency(
+            ui::INPUT_EVENT_LATENCY_RENDERING_SCHEDULED_IMPL_COMPONENT,
+            0, &rendering_scheduled_component))
+      return;
+  }
+
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      rendering_scheduled_on_main ?

[Alexei Svitkine (slow), 2015/02/12 15:31:32]

This is not valid to do.

Histogram macros cache the histogram object on first hit, so this ternary will
do nothing on the next invocation.

[Yufeng Shen (Slow to review), 2015/02/12 21:33:25]

Thanks for pointing this out.

+      "Event.Latency.ScrollUpdateTouchToHandledMain" :
+      "Event.Latency.ScrollUpdateTouchToHandledImpl",
+      (rendering_scheduled_component.event_time -
+       original_component.event_time).InMicroseconds(),
+      1, 1000000, 100);
+
+  LatencyInfo::LatencyComponent renderer_swap_component;
+  if (!latency.FindLatency(ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT,
+                           0, &renderer_swap_component))
+    return;
+
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      rendering_scheduled_on_main ?
+      "Event.Latency.ScrollUpdateHandledMainToRendererSwap" :
+      "Event.Latency.ScrollUpdateHandledImplToRendererSwap",
+      (renderer_swap_component.event_time -
+       rendering_scheduled_component.event_time).
+      InMicroseconds(),
+      1, 1000000, 100);
+
+  LatencyInfo::LatencyComponent browser_received_swap_component;
+  if (!latency.FindLatency(
+          ui::INPUT_EVENT_BROWSER_RECEIVED_RENDERER_SWAP_COMPONENT,
+          0, &browser_received_swap_component))
+    return;
+
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      "Event.Latency.ScrollUpdateRendererSwapToBrowserNotified",
+      (browser_received_swap_component.event_time -
+       renderer_swap_component.event_time).InMicroseconds(),
+      1, 1000000, 100);
+
+  LatencyInfo::LatencyComponent gpu_swap_component;
+  if (!latency.FindLatency(ui::INPUT_EVENT_GPU_SWAP_BUFFER_COMPONENT,
+                           0, &gpu_swap_component))
+    return;
+
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      "Event.Latency.ScrollUpdateBrowserNotifiedToBeforeGpuSwap",
+      (gpu_swap_component.event_time -
+       browser_received_swap_component.event_time).InMicroseconds(),
+      1, 1000000, 100);

[Alexei Svitkine (slow), 2015/02/12 15:31:33]

If you're using the same ranges for all of these, please make a helper macro
instead of duplicating these constants. Along with a comment explaining why
those values were chosen.

[Yufeng Shen (Slow to review), 2015/02/12 21:33:25]

Done.

+
+  UMA_HISTOGRAM_CUSTOM_COUNTS(
+      "Event.Latency.ScrollUpdateGpuSwap",
+      (swap_component.event_time -
+       gpu_swap_component.event_time).InMicroseconds(),
+      1, 1000000, 100);
 }
 
 // LatencyComponents generated in the renderer must have component IDs
@@ -264,7 +327,9 @@ void RenderWidgetHostLatencyTracker::OnInputEventAck(
 
   // Latency ends when it is acked but does not cause render scheduling.
   bool rendering_scheduled = latency->FindLatency(
-      ui::INPUT_EVENT_LATENCY_RENDERING_SCHEDULED_COMPONENT, 0, NULL);
+      ui::INPUT_EVENT_LATENCY_RENDERING_SCHEDULED_MAIN_COMPONENT, 0, nullptr);
+  rendering_scheduled |= latency->FindLatency(
+      ui::INPUT_EVENT_LATENCY_RENDERING_SCHEDULED_IMPL_COMPONENT, 0, nullptr);
 
   if (WebInputEvent::isGestureEventType(event.type)) {
     if (!rendering_scheduled) {