Add a sampling scheme to ScrollUpdate.Touch UKM

content/browser/renderer_host/input/render_widget_host_latency_tracker.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/input/render_widget_host_latency_tracker.h"
 
 #include <stddef.h>
 
 #include "base/logging.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/rand_util.h"
 #include "build/build_config.h"
 #include "components/rappor/public/rappor_utils.h"
 #include "content/browser/renderer_host/render_widget_host_delegate.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/common/content_client.h"
 #include "services/metrics/public/cpp/ukm_entry_builder.h"
 #include "ui/events/blink/web_input_event_traits.h"
 #include "ui/latency/latency_histogram_macros.h"
 
 using blink::WebGestureEvent;
 using blink::WebInputEvent;
 using blink::WebMouseEvent;
 using blink::WebMouseWheelEvent;
 using blink::WebTouchEvent;
 using ui::LatencyInfo;
 
 namespace content {
 namespace {
 
+constexpr int kSamplingInterval = 10;
+
 std::string WebInputEventTypeToInputModalityString(WebInputEvent::Type type) {
   if (type == blink::WebInputEvent::kMouseWheel) {
     return "Wheel";
   } else if (WebInputEvent::IsKeyboardEventType(type)) {
     // We should only be reporting latency for key presses.
     DCHECK(type == WebInputEvent::kRawKeyDown || type == WebInputEvent::kChar);
     return "KeyPress";
   } else if (WebInputEvent::IsMouseEventType(type)) {
     return "Mouse";
   } else if (WebInputEvent::IsTouchEventType(type)) {
@@ skipping 89 matching lines @@
   if (expected_queueing_time_ms > 450) {
     UMA_HISTOGRAM_TIMES(
         "RendererScheduler."
         "QueueingDurationWhenExpectedQueueingTime_GreaterThan.450ms",
         queueing_time);
   }
 }
 
 }  // namespace
 
-RenderWidgetHostLatencyTracker::RenderWidgetHostLatencyTracker()
+RenderWidgetHostLatencyTracker::RenderWidgetHostLatencyTracker(
+    bool metric_sampling)
     : ukm_source_id_(-1),
       last_event_id_(0),
       latency_component_id_(0),
       device_scale_factor_(1),
       has_seen_first_gesture_scroll_update_(false),
       active_multi_finger_gesture_(false),
       touch_start_default_prevented_(false),
-      render_widget_host_delegate_(nullptr) {}
+      metric_sampling_(metric_sampling),
+      metric_sampling_countdown_(-1),
+      render_widget_host_delegate_(nullptr) {
+  if (metric_sampling)
+    metric_sampling_countdown_ = base::RandUint64() % kSamplingInterval;
+}
 
 RenderWidgetHostLatencyTracker::~RenderWidgetHostLatencyTracker() {}
 
 void RenderWidgetHostLatencyTracker::Initialize(int routing_id,
                                                 int process_id) {
   DCHECK_EQ(0, last_event_id_);
   DCHECK_EQ(0, latency_component_id_);
   last_event_id_ = static_cast<int64_t>(process_id) << 32;
   latency_component_id_ = routing_id | last_event_id_;
 }
@@ skipping 247 matching lines @@
   return ukm_source_id_;
 }
 
 void RenderWidgetHostLatencyTracker::ReportUkmScrollLatency(
     const std::string& event_name,
     const std::string& metric_name,
     const LatencyInfo::LatencyComponent& start_component,
     const LatencyInfo::LatencyComponent& end_component) {
   CONFIRM_VALID_TIMING(start_component, end_component)
 
+  // Only report a subset of this metric as the volume is too high.
+  if (event_name == "Event.ScrollUpdate.Touch") {
+    metric_sampling_countdown_++;

[tdresser, 2017/07/17 20:25:22]

"countdown" implies it counts down, but it counts up!

I'm not sure what the best name would be though.
metric_sampling_events_since_last_sample ?

Any better ideas?

[Navid Zolghadr, 2017/07/19 15:57:46]

Done.

+    metric_sampling_countdown_ %= kSamplingInterval;
+    if (metric_sampling_ && metric_sampling_countdown_)
+      return;
+    metric_sampling_countdown_ = 0;

[dtapuska, 2017/07/17 20:21:41]

This line is useless.

[Navid Zolghadr, 2017/07/19 15:57:46]

Done.

+  }
+
   ukm::SourceId ukm_source_id = GetUkmSourceId();
   ukm::UkmRecorder* ukm_recorder = ukm::UkmRecorder::Get();
 
   if (ukm_source_id == -1 || !ukm_recorder)
     return;
 
   std::unique_ptr<ukm::UkmEntryBuilder> builder =
       ukm_recorder->GetEntryBuilder(ukm_source_id, event_name.c_str());
   builder->AddMetric(metric_name.c_str(), (end_component.last_event_time -
                                            start_component.first_event_time)
                                               .InMicroseconds());
 }
 }  // namespace content