Initialize the TaskScheduler with Variation Parameters if Available

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index d1a7a6e3866a7442a68adb0d2c8ef6b4d0b92f2d..2310715b8d30256c2e507ace92d26eead8fd9fb1 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -7,6 +7,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <algorithm>
+#include <map>
 #include <set>
 #include <string>
 #include <utility>
@@ -21,6 +23,7 @@
 #include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
+#include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
@@ -33,6 +36,9 @@
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
+#include "base/task_scheduler/scheduler_worker_pool_params.h"
+#include "base/task_scheduler/task_scheduler.h"
+#include "base/task_scheduler/task_traits.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/default_tick_clock.h"
 #include "base/time/time.h"
@@ -317,6 +323,128 @@ void AddFirstRunNewTabs(StartupBrowserCreator* browser_creator,
 }
 #endif  // !defined(OS_ANDROID) && !defined(OS_CHROMEOS)
 
+enum WorkerPoolType : size_t {
+  BACKGROUND_WORKER_POOL = 0,
+  BACKGROUND_FILE_IO_WORKER_POOL,
+  FOREGROUND_WORKER_POOL,
+  FOREGROUND_FILE_IO_WORKER_POOL,
+  WORKER_POOL_COUNT  // Always last.
+};
+
+struct WorkerPoolVariationValues {
+  int threads = 0;
+  base::TimeDelta detach_period;
+};
+
+// Converts |pool_descriptor| to a WorkerPoolVariationValues. Returns a default
+// WorkerPoolVariationValues on failure.
+//
+// |pool_descriptor| is a comma separated value string with the following items:
+// 1. Minimum Thread Count (int)
+// 2. Maximum Thread Count (int)
+// 3. Thread Count Multiplier (double)
+// 4. Thread Count Offset (int)
+// 5. Detach Time in Milliseconds (milliseconds)
+// Additional values may appear as necessary and will be ignored.
+WorkerPoolVariationValues StringToWorkerPoolVariationValues(
+    const base::StringPiece pool_descriptor) {
+  const std::vector<std::string> tokens =
+      SplitString(pool_descriptor, ",",
+                  base::KEEP_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
+  int minimum;
+  int maximum;
+  double multiplier;
+  int offset;
+  int detach_milliseconds;
+  // Checking for a size greater than the expected amount allows us to be
+  // forward compatible if we add more variation values.
+  if (tokens.size() >= 5 &&
+      base::StringToInt(tokens[0], &minimum) &&
+      base::StringToInt(tokens[1], &maximum) &&
+      base::StringToDouble(tokens[2], &multiplier) &&
+      base::StringToInt(tokens[3], &offset) &&
+      base::StringToInt(tokens[4], &detach_milliseconds)) {
+    const int num_of_cores = base::SysInfo::NumberOfProcessors();
+    const int threads = std::ceil<int>(num_of_cores * multiplier) + offset;
+    WorkerPoolVariationValues values;
+    values.threads = std::min(maximum, std::max(minimum, threads));
+    values.detach_period =
+        base::TimeDelta::FromMilliseconds(detach_milliseconds);
+    return values;
+  }
+  DLOG(ERROR) << "Invalid Worker Pool Descriptor: " << pool_descriptor;
+  return WorkerPoolVariationValues();
+}
+
+// Returns the worker pool index for |traits| defaulting to
+// FOREGROUND_WORKER_POOL or FOREGROUND_FILE_IO_WORKER_POOL on unknown
+// priorities.
+size_t WorkerPoolIndexForTraits(const base::TaskTraits& traits) {
+  const bool is_background =
+      traits.priority() == base::TaskPriority::BACKGROUND;
+  if (traits.with_file_io()) {
+    return is_background ? BACKGROUND_FILE_IO_WORKER_POOL
+                         : FOREGROUND_FILE_IO_WORKER_POOL;
+  }
+  return is_background ? BACKGROUND_WORKER_POOL : FOREGROUND_WORKER_POOL;
+}
+
+// Initializes the Default Browser Task Scheduler if there is a valid variation
+// parameter for the field trial.
+void MaybeInitializeTaskScheduler() {
+  static constexpr char kFieldTrialName[] = "BrowserScheduler";
+  std::map<std::string, std::string> variation_params;
+  if (!variations::GetVariationParams(kFieldTrialName, &variation_params))
+    return;
+
+  using ThreadPriority = base::ThreadPriority;
+  using IORestriction = base::SchedulerWorkerPoolParams::IORestriction;
+  struct SchedulerWorkerPoolPredefinedParams {
+    const char* name;
+    ThreadPriority priority_hint;
+    IORestriction io_restriction;
+  };
+  static const SchedulerWorkerPoolPredefinedParams kAllPredefinedParams[] = {
+    {"Background", ThreadPriority::BACKGROUND, IORestriction::DISALLOWED},
+    {"BackgroundFileIO", ThreadPriority::BACKGROUND, IORestriction::ALLOWED},
+    {"Foreground", ThreadPriority::NORMAL, IORestriction::DISALLOWED},
+    {"ForegroundFileIO", ThreadPriority::NORMAL, IORestriction::ALLOWED},
+  };
+  static_assert(arraysize(kAllPredefinedParams) == WORKER_POOL_COUNT,
+                "Mismatched Worker Pool Types and Predefined Parameters");
+
+  std::vector<base::SchedulerWorkerPoolParams> params_vector;
+  for (const auto& predefined_params : kAllPredefinedParams) {
+    const auto pair = variation_params.find(predefined_params.name);
+    if (pair == variation_params.end()) {
+      DLOG(ERROR) << "Missing Worker Pool Configuration: "
+                  << predefined_params.name;
+      return;
+    }
+
+    const WorkerPoolVariationValues variation_values =
+        StringToWorkerPoolVariationValues(pair->second);
+
+    if (variation_values.threads <= 0 ||
+        variation_values.detach_period.is_zero()) {
+      DLOG(ERROR) << "Invalid Worker Pool Configuration: " <<
+          predefined_params.name << " [" << pair->second << "]";
+      return;
+    }
+
+    params_vector.emplace_back(predefined_params.name,
+                               predefined_params.priority_hint,
+                               predefined_params.io_restriction,
+                               variation_values.threads,
+                               variation_values.detach_period);
+  }
+
+  DCHECK_EQ(WORKER_POOL_COUNT, params_vector.size());
+
+  base::TaskScheduler::CreateAndSetDefaultTaskScheduler(
+      params_vector, base::Bind(WorkerPoolIndexForTraits));
+}
+
 // Returns the new local state object, guaranteed non-NULL.
 // |local_state_task_runner| must be a shutdown-blocking task runner.
 PrefService* InitializeLocalState(
@@ -1214,6 +1342,8 @@ int ChromeBrowserMainParts::PreCreateThreadsImpl() {
   // IOThread's initialization which happens in BrowserProcess:PreCreateThreads.
   SetupMetricsAndFieldTrials();
 
+  MaybeInitializeTaskScheduler();
+
   // ChromeOS needs ResourceBundle::InitSharedInstance to be called before this.
   browser_process_->PreCreateThreads();