Bug 1800412 - Add a preference to control whether the EcoQoS is used for background content processes, r=gsvelto.

Differential Revision: https://phabricator.services.mozilla.com/D161975

browser/app/profile/firefox.js

@@ -2076,6 +2076,10 @@ pref("extensions.experiments.enabled", false);
   pref("dom.ipc.processPriorityManager.enabled", true);
 #endif
 
+#if defined(XP_WIN)
+  pref("dom.ipc.processPriorityManager.backgroundUsesEcoQoS", true);
+#endif
+
 // Don't limit how many nodes we care about on desktop:
 pref("reader.parse-node-limit", 0);
 

hal/windows/WindowsProcessPriority.cpp

@@ -11,6 +11,7 @@
 #include "Hal.h"
 #include "HalLog.h"
 #include "nsWindowsHelpers.h"  // for nsAutoHandle and nsModuleHandle
+#include "mozilla/StaticPrefs_dom.h"
 
 #include <windows.h>
 
@@ -42,6 +43,11 @@ void SetProcessPriority(int aPid, ProcessPriority aPriority) {
     static bool alreadyInitialized = false;
     static decltype(::SetProcessInformation)* setProcessInformation = nullptr;
     if (!alreadyInitialized) {
+      if (aPriority == PROCESS_PRIORITY_PARENT_PROCESS ||
+          !StaticPrefs::dom_ipc_processPriorityManager_backgroundUsesEcoQoS()) {
+        return;
+      }
+
       alreadyInitialized = true;
       // SetProcessInformation only exists on Windows 8 and later.
       nsModuleHandle module(LoadLibrary(L"Kernel32.dll"));
@@ -59,9 +65,12 @@ void SetProcessPriority(int aPid, ProcessPriority aPriority) {
     RtlZeroMemory(&PowerThrottling, sizeof(PowerThrottling));
     PowerThrottling.Version = PROCESS_POWER_THROTTLING_CURRENT_VERSION;
     PowerThrottling.ControlMask = PROCESS_POWER_THROTTLING_EXECUTION_SPEED;
-    PowerThrottling.StateMask = aPriority == PROCESS_PRIORITY_BACKGROUND
-                                    ? PROCESS_POWER_THROTTLING_EXECUTION_SPEED
-                                    : 0;
+    PowerThrottling.StateMask =
+        (aPriority == PROCESS_PRIORITY_BACKGROUND) &&
+                StaticPrefs::
+                    dom_ipc_processPriorityManager_backgroundUsesEcoQoS()
+            ? PROCESS_POWER_THROTTLING_EXECUTION_SPEED
+            : 0;
     if (setProcessInformation(processHandle, ProcessPowerThrottling,
                               &PowerThrottling, sizeof(PowerThrottling))) {
       HAL_LOG("SetProcessInformation(%d, %s)\n", aPid,

modules/libpref/init/StaticPrefList.yaml

@@ -2863,6 +2863,13 @@
 #endif
   mirror: always
 
+#ifdef XP_WIN
+- name: dom.ipc.processPriorityManager.backgroundUsesEcoQoS
+  type: bool
+  value: false
+  mirror: always
+#endif
+
 # Is support for HTMLElement.autocapitalize enabled?
 - name: dom.forms.autocapitalize
   type: bool