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..a4bb02131838b0614a4250adfc0225edc5c67978 100644
--- a/content/browser/renderer_host/render_widget_host_latency_tracker.cc
+++ b/content/browser/renderer_host/render_widget_host_latency_tracker.cc
@@ -135,6 +135,13 @@ void ComputeInputLatencyHistograms(WebInputEvent::Type type,
   }
 }
 
+// Scroll latency is mostly under 1000ms.
+#define UMA_HISTOGRAM_SCROLL_LATENCY(name, end, start)        \

[jdduke (slow), 2015/02/12 21:44:08]

The end vs start arg order is a little confusing when reading the code below, if
it's not too much trouble could we reverse it?

[Yufeng Shen (Slow to review), 2015/02/12 22:04:56]

Done.

+  UMA_HISTOGRAM_CUSTOM_COUNTS(                                \
+    name,                                                     \
+    (end.event_time - start.event_time).InMicroseconds(),     \
+    1, 1000000, 100)
+
 void ComputeScrollLatencyHistograms(
     const LatencyInfo::LatencyComponent& swap_component,
     int64 latency_component_id,
@@ -148,11 +155,9 @@ void ComputeScrollLatencyHistograms(
     // first scroll event in a sequence and the original timestamp of that
     // scroll event's underlying touch event.
     for (size_t i = 0; i < first_original_component.event_count; i++) {
-      UMA_HISTOGRAM_CUSTOM_COUNTS(
+      UMA_HISTOGRAM_SCROLL_LATENCY(
           "Event.Latency.TouchToFirstScrollUpdateSwap",
-          (swap_component.event_time - first_original_component.event_time)
-              .InMicroseconds(),
-          1, 1000000, 100);
+          swap_component, first_original_component);
     }
     original_component = first_original_component;
   } else if (!latency.FindLatency(
@@ -165,12 +170,69 @@ void ComputeScrollLatencyHistograms(
   // created (averaged if there are multiple) to when the scroll gesture
   // results in final frame swap.
   for (size_t i = 0; i < original_component.event_count; i++) {
-    UMA_HISTOGRAM_CUSTOM_COUNTS(
+    UMA_HISTOGRAM_SCROLL_LATENCY(
         "Event.Latency.TouchToScrollUpdateSwap",
-        (swap_component.event_time - original_component.event_time)
-            .InMicroseconds(),
-        1, 1000000, 100);
+        swap_component, original_component);
+  }
+
+  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;
+  }
+
+  if (rendering_scheduled_on_main) {
+    UMA_HISTOGRAM_SCROLL_LATENCY(
+        "Event.Latency.ScrollUpdate.TouchToHandled_Main",
+        rendering_scheduled_component, original_component);
+  } else {
+    UMA_HISTOGRAM_SCROLL_LATENCY(
+        "Event.Latency.ScrollUpdate.TouchToHandled_Impl",
+        rendering_scheduled_component, original_component);
+  }
+
+  LatencyInfo::LatencyComponent renderer_swap_component;
+  if (!latency.FindLatency(ui::INPUT_EVENT_LATENCY_RENDERER_SWAP_COMPONENT,
+                           0, &renderer_swap_component))
+    return;
+
+  if (rendering_scheduled_on_main) {
+    UMA_HISTOGRAM_SCROLL_LATENCY(
+        "Event.Latency.ScrollUpdate.HandledToRendererSwap_Main",
+        renderer_swap_component, rendering_scheduled_component);
+  } else {
+    UMA_HISTOGRAM_SCROLL_LATENCY(
+        "Event.Latency.ScrollUpdate.HandledToRendererSwap_Impl",
+        renderer_swap_component, rendering_scheduled_component);
   }
+
+  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_SCROLL_LATENCY(
+      "Event.Latency.ScrollUpdate.RendererSwapToBrowserNotified",
+      browser_received_swap_component, renderer_swap_component);
+
+  LatencyInfo::LatencyComponent gpu_swap_component;
+  if (!latency.FindLatency(ui::INPUT_EVENT_GPU_SWAP_BUFFER_COMPONENT,
+                           0, &gpu_swap_component))
+    return;
+
+  UMA_HISTOGRAM_SCROLL_LATENCY(
+      "Event.Latency.ScrollUpdate.BrowserNotifiedToBeforeGpuSwap",
+      gpu_swap_component, browser_received_swap_component);
+
+  UMA_HISTOGRAM_SCROLL_LATENCY("Event.Latency.ScrollUpdate.GpuSwap",
+                               swap_component, gpu_swap_component);
 }
 
 // LatencyComponents generated in the renderer must have component IDs
@@ -264,7 +326,9 @@ 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) {