Add a flag to configure the gamepad polling interval

Adds --gamepad-polling-interval [INTERVAL], where INTERVAL is the delay
in milliseconds between successive polls of gamepad button and axis
inputs. Decreasing the interval improves latency, but may cause a loss
in performance due to more CPU time spent in the input polling thread.
The interval must be between 4 and 16 ms, inclusive. If no interval is
specified the max value (16ms) is used.

Also adds chrome://flags#gamepad-polling-rate to allow selection of the
target polling rate from the flags page.

BUG=855188

Change-Id: I9ec58c7320eff952c46bce263da8526459ad8a9b
Reviewed-on: https://chromium-review.googlesource.com/1110742
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571227}

chrome/browser/BUILD.gn

@@ -1819,6 +1819,7 @@ jumbo_split_static_library("browser") {
     "//crypto:platform",
     "//device/base",
     "//device/fido",
+    "//device/gamepad/public/cpp:switches",
     "//device/usb/mojo",
     "//device/usb/public/mojom",
     "//device/vr/buildflags",

chrome/browser/DEPS

@@ -26,6 +26,7 @@ include_rules = [
   "+device/bluetooth",
   "+device/fido",
   "+device/geolocation/public/cpp",
+  "+device/gamepad/public/cpp",
   "+device/usb",
   "+device/vr/buildflags/buildflags.h",
   "+extensions/browser",

chrome/browser/about_flags.cc

@@ -105,6 +105,7 @@
 #include "content/public/common/content_switches.h"
 #include "content/public/common/feature_h264_with_openh264_ffmpeg.h"
 #include "device/base/features.h"
+#include "device/gamepad/public/cpp/gamepad_switches.h"
 #include "device/vr/buildflags/buildflags.h"
 #include "extensions/buildflags/buildflags.h"
 #include "google_apis/drive/drive_switches.h"
@@ -1155,6 +1156,14 @@ const FeatureEntry::FeatureVariation kProactiveTabFreezeAndDiscardVariations[] =
       base::size(kProactiveTabFreezeAndDiscard_FreezeAndDiscard), nullptr}};
 #endif
 
+const FeatureEntry::Choice kGamepadPollingRateChoices[] = {
+    {"60 Hz (Default)", "", ""},  // 16 ms, technically 62.5 Hz
+    {"100 Hz", switches::kGamepadPollingInterval, "10"},
+    {"125 Hz", switches::kGamepadPollingInterval, "8"},
+    {"200 Hz", switches::kGamepadPollingInterval, "5"},
+    {"250 Hz", switches::kGamepadPollingInterval, "4"},
+};
+
 // RECORDING USER METRICS FOR FLAGS:
 // -----------------------------------------------------------------------------
 // The first line of the entry is the internal name.
@@ -3996,6 +4005,10 @@ const FeatureEntry kFeatureEntries[] = {
      FEATURE_VALUE_TYPE(features::kArcCupsApi)},
 #endif  // OS_CHROMEOS
 
+    {"gamepad-polling-rate", flag_descriptions::kGamepadPollingRateName,
+     flag_descriptions::kGamepadPollingRateDescription, kOsDesktop,
+     MULTI_VALUE_TYPE(kGamepadPollingRateChoices)},
+
     // NOTE: Adding a new flag requires adding a corresponding entry to enum
     // "LoginCustomFlags" in tools/metrics/histograms/enums.xml. See "Flag
     // Histograms" in tools/metrics/histograms/README.md (run the

chrome/browser/flag_descriptions.cc

@@ -880,6 +880,11 @@ const char kFramebustingDescription[] =
 const char kGamepadExtensionsName[] = "Gamepad Extensions";
 const char kGamepadExtensionsDescription[] =
     "Enables experimental extensions to the Gamepad APIs.";
+const char kGamepadPollingRateName[] = "Gamepad Polling Rate";
+const char kGamepadPollingRateDescription[] =
+    "Changes the rate at which gamepad input devices are polled. Increasing "
+    "the polling rate improves the average latency of button and axis inputs "
+    "but may negatively affect performance.";
 const char kGamepadVibrationName[] = "Gamepad Vibration";
 const char kGamepadVibrationDescription[] =
     "Enables haptic vibration effects on supported gamepads.";

chrome/browser/flag_descriptions.h

@@ -550,6 +550,8 @@ extern const char kFramebustingDescription[];
 
 extern const char kGamepadExtensionsName[];
 extern const char kGamepadExtensionsDescription[];
+extern const char kGamepadPollingRateName[];
+extern const char kGamepadPollingRateDescription[];
 extern const char kGamepadVibrationName[];
 extern const char kGamepadVibrationDescription[];
 

device/gamepad/BUILD.gn

@@ -89,6 +89,7 @@ component("gamepad") {
     "//base/third_party/dynamic_annotations",
     "//device/base/synchronization",
     "//device/gamepad/public/cpp:shared_with_blink",
+    "//device/gamepad/public/cpp:switches",
     "//device/gamepad/public/mojom",
     "//mojo/public/cpp/system",
     "//third_party/blink/public:blink_headers",

device/gamepad/gamepad_provider.cc

@@ -11,10 +11,12 @@
 #include <vector>
 
 #include "base/bind.h"
+#include "base/command_line.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "base/single_thread_task_runner.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
@@ -23,10 +25,18 @@
 #include "device/gamepad/gamepad_data_fetcher.h"
 #include "device/gamepad/gamepad_data_fetcher_manager.h"
 #include "device/gamepad/gamepad_user_gesture.h"
+#include "device/gamepad/public/cpp/gamepad_switches.h"
 #include "mojo/public/cpp/system/platform_handle.h"
 
 namespace device {
 
+namespace {
+
+const size_t kPollingIntervalMillisecondsMin = 4;   // ~250 Hz
+const size_t kPollingIntervalMillisecondsMax = 16;  // ~62.5 Hz
+
+}  // namespace
+
 GamepadProvider::ClosureAndThread::ClosureAndThread(
     const base::Closure& c,
     const scoped_refptr<base::SingleThreadTaskRunner>& m)
@@ -185,6 +195,22 @@ void GamepadProvider::OnDevicesChanged(base::SystemMonitor::DeviceType type) {
 }
 
 void GamepadProvider::Initialize(std::unique_ptr<GamepadDataFetcher> fetcher) {
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  size_t interval_millis = kPollingIntervalMillisecondsMax;
+  if (command_line &&
+      command_line->HasSwitch(switches::kGamepadPollingInterval)) {
+    std::string string_value =
+        command_line->GetSwitchValueASCII(switches::kGamepadPollingInterval);
+    size_t int_value;
+    if (base::StringToSizeT(string_value, &int_value)) {
+      // Clamp interval duration to valid range.
+      int_value = std::max(int_value, kPollingIntervalMillisecondsMin);
+      int_value = std::min(int_value, kPollingIntervalMillisecondsMax);
+      interval_millis = int_value;
+    }
+  }
+  sampling_interval_delta_ = base::TimeDelta::FromMilliseconds(interval_millis);
+
   base::SystemMonitor* monitor = base::SystemMonitor::Get();
   if (monitor)
     monitor->AddDevicesChangedObserver(this);
@@ -372,7 +398,7 @@ void GamepadProvider::ScheduleDoPoll() {
 
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE, base::BindOnce(&GamepadProvider::DoPoll, Unretained(this)),
-      base::TimeDelta::FromMilliseconds(kDesiredSamplingIntervalMs));
+      sampling_interval_delta_);
   have_scheduled_do_poll_ = true;
 }
 

device/gamepad/gamepad_provider.h

@@ -15,6 +15,7 @@
 #include "base/memory/shared_memory.h"
 #include "base/synchronization/lock.h"
 #include "base/system_monitor/system_monitor.h"
+#include "base/time/time.h"
 #include "device/gamepad/gamepad_export.h"
 #include "device/gamepad/gamepad_pad_state_provider.h"
 #include "device/gamepad/gamepad_shared_buffer.h"
@@ -114,7 +115,8 @@ class DEVICE_GAMEPAD_EXPORT GamepadProvider
   // true if any user gesture observers were notified.
   bool CheckForUserGesture();
 
-  enum { kDesiredSamplingIntervalMs = 16 };
+  // The duration of the delay between iterations of DoPoll.
+  base::TimeDelta sampling_interval_delta_;
 
   // Keeps track of when the background thread is paused. Access to is_paused_
   // must be guarded by is_paused_lock_.

device/gamepad/public/cpp/BUILD.gn

@@ -41,3 +41,10 @@ component("shared_typemap_traits") {
     "//device/gamepad/public/mojom:mojom_shared",
   ]
 }
+
+static_library("switches") {
+  sources = [
+    "gamepad_switches.cc",
+    "gamepad_switches.h",
+  ]
+}

device/gamepad/public/cpp/gamepad_switches.cc

+// Copyright 2018 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 "device/gamepad/public/cpp/gamepad_switches.h"
+
+namespace switches {
+
+// Overrides the gamepad polling interval. Decreasing the interval improves
+// input latency of buttons and axes but may negatively affect performance due
+// to more CPU time spent in the input polling thread.
+const char kGamepadPollingInterval[] = "gamepad-polling-interval";
+
+}  // namespace switches

device/gamepad/public/cpp/gamepad_switches.h

+// Copyright 2018 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.
+
+#ifndef DEVICE_GAMEPAD_PUBLIC_CPP_GAMEPAD_SWITCHES_H_
+#define DEVICE_GAMEPAD_PUBLIC_CPP_GAMEPAD_SWITCHES_H_
+
+namespace switches {
+
+// All switches in alphabetical order. The switches should be documented
+// alongside the definition of their values in the .cc file.
+extern const char kGamepadPollingInterval[];
+
+}  // namespace switches
+
+#endif  // DEVICE_GAMEPAD_PUBLIC_CPP_GAMEPAD_SWITCHES_H_

tools/metrics/histograms/enums.xml

@@ -28460,6 +28460,7 @@ from previous Chrome versions.
   <int value="1209221384" label="enable-experimental-accessibility-features"/>
   <int value="1210343926" label="enable-drop-sync-credential"/>
   <int value="1211284676" label="V8NoTurbo:enabled"/>
+  <int value="1214219155" label="gamepad-polling-interval"/>
   <int value="1214455758" label="VideoRotateToFullscreen:disabled"/>
   <int value="1215531732" label="OmniboxUIExperiments:disabled"/>
   <int value="1217907443" label="spurious-power-button-keyboard-accel"/>