blob: 302e41b47c75bb4c5ddefcb2da7cef70f2ffd6e2 [file] [log] [blame]
// Copyright 2019 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 "ui/events/blink/momentum_scroll_jank_tracker.h"
#include "base/metrics/histogram_functions.h"
#include "ui/events/blink/blink_event_util.h"
#include "ui/events/blink/event_with_callback.h"
namespace ui {
constexpr base::TimeDelta MomentumScrollJankTracker::kRecentEventCutoff;
MomentumScrollJankTracker::~MomentumScrollJankTracker() {
// Don't log if this scroll had no momentum input (after the first event).
if (total_event_count_ == 0)
// We want to target 0 janks, so round our percentages up so that a single
// jank over a large number of frames doesn't get lost.
// Don't worry about overflow as we'd need a gesture > 100hrs long to hit,
// and the downside is an incorrect metric.
uint32_t rounding_factor = total_event_count_ - 1;
uint32_t jank_percentage =
(jank_count_ * 100 + rounding_factor) / total_event_count_;
uint32_t ordering_jank_percentage =
(ordering_jank_count_ * 100 + rounding_factor) / total_event_count_;
void MomentumScrollJankTracker::OnDispatchedInputEvent(
EventWithCallback* event_with_callback,
const base::TimeTicks& now) {
const auto& gesture_event = ToWebGestureEvent(event_with_callback->event());
// If the scroll is not in the momentum phase, it's driven by user input,
// which happens at a higher frequency. Ignore this.
if ( !=
blink::WebGestureEvent::InertialPhaseState::kMomentum) {
// Ignore the first momentum input event, as this may happen out-of band
// with BeginFrame, and may be coalesced in a non-jank scenario.
// TODO(ericrk): Add a metric to track jank in the transition from user
// to momentum input.
if (!seen_first_momentum_input_) {
seen_first_momentum_input_ = true;
total_event_count_ += event_with_callback->coalesced_count();
jank_count_ +=
event_with_callback->coalesced_count() - kExpectedMomentumEventsPerFrame;
// To isolate the case where we are processing events ~every frame but
// still experiencing jank due unstable ordering of event delivery wrt.
// begin frame, check if this event has been coalesced exactly once more
// than expected and if that coalescing happened within kRecentEventCutoff.
bool one_extra_event = event_with_callback->coalesced_count() ==
kExpectedMomentumEventsPerFrame + 1;
bool coalesced_recently =
(now - event_with_callback->last_coalesced_timestamp()) <
if (one_extra_event && coalesced_recently)
} // namespace ui