Add product flag for enabling all processor groups

src/hotspot/os/windows/globals_windows.hpp

@@ -36,6 +36,9 @@
                          range,                                           \
                          constraint)                                      \
                                                                           \
+product(bool, UseAllWindowsProcessorGroups, false,                        \
+        "Use all processor groups on supported Windows versions")         \
+                                                                          \
 product(bool, UseOSErrorReporting, false,                                 \
         "Let VM fatal error propagate to the OS (ie. WER on Windows)")
 

src/hotspot/os/windows/os_windows.cpp

@@ -868,19 +868,22 @@ int os::active_processor_count() {
     return ActiveProcessorCount;
   }
 
-  // Starting with Windows 11 and Windows Server 2022, the OS has changed to
-  // make processes and their threads span all processors in the system,
-  // across all processor groups, by default. Therefore, we will allow all
-  // processors to be active processors on these operating systems. However,
-  // job objects can be used to restrict processor affinity across the
-  // processor groups. In this case, the number of active processors must be
-  // obtained from the processor affinity in the job object.
-  bool schedules_all_processor_groups = win32::is_windows_11_or_greater() || win32::is_windows_server_2022_or_greater();
-  if (schedules_all_processor_groups) {
-    DWORD processors_in_job_object = win32::active_processors_in_job_object();
-
-    if (processors_in_job_object > 0) {
-      return processors_in_job_object;
+  bool schedules_all_processor_groups = false;
+  if (UseAllWindowsProcessorGroups) {
+    // Starting with Windows 11 and Windows Server 2022, the OS has changed to
+    // make processes and their threads span all processors in the system,
+    // across all processor groups, by default. Therefore, we will allow all
+    // processors to be active processors on these operating systems. However,
+    // job objects can be used to restrict processor affinity across the
+    // processor groups. In this case, the number of active processors must be
+    // obtained from the processor affinity in the job object.
+    schedules_all_processor_groups = win32::is_windows_11_or_greater() || win32::is_windows_server_2022_or_greater();
+    if (schedules_all_processor_groups) {
+      DWORD processors_in_job_object = win32::active_processors_in_job_object();
+
+      if (processors_in_job_object > 0) {
+        return processors_in_job_object;
+      }
     }
   }
 
@@ -902,17 +905,19 @@ int os::active_processor_count() {
     warning("GetProcessAffinityMask() failed: GetLastError->%ld.", GetLastError());
   }
 
-  // There are no processor affinity restrictions at this point so we can return
-  // the overall processor count if the OS automatically schedules threads across
-  // all processors on the system. Note that older operating systems can
-  // correctly report processor count but will not schedule threads across
-  // processor groups unless the application explicitly uses group affinity APIs
-  // to assign threads to processor groups. On these older operating systems, we
-  // will continue to use the dwNumberOfProcessors field. For details on the
-  // latest Windows scheduling behavior, see
-  // https://learn.microsoft.com/en-us/windows/win32/procthread/processor-groups#behavior-starting-with-windows-11-and-windows-server-2022
-  if (schedules_all_processor_groups) {
-    logical_processors = processor_count();
+  if (UseAllWindowsProcessorGroups) {
+    // There are no processor affinity restrictions at this point so we can return
+    // the overall processor count if the OS automatically schedules threads across
+    // all processors on the system. Note that older operating systems can
+    // correctly report processor count but will not schedule threads across
+    // processor groups unless the application explicitly uses group affinity APIs
+    // to assign threads to processor groups. On these older operating systems, we
+    // will continue to use the dwNumberOfProcessors field. For details on the
+    // latest Windows scheduling behavior, see
+    // https://learn.microsoft.com/en-us/windows/win32/procthread/processor-groups#behavior-starting-with-windows-11-and-windows-server-2022
+    if (schedules_all_processor_groups) {
+      logical_processors = processor_count();
+    }
   }
 
   return logical_processors == 0 ? si.dwNumberOfProcessors : logical_processors;

test/hotspot/gtest/runtime/test_os_windows.cpp

@@ -704,14 +704,17 @@ TEST_VM(os_windows, reserve_memory_special) {
 }
 
 TEST_VM(os_windows, processor_count) {
+  JVMFlag* flag = JVMFlag::find_flag("UseAllWindowsProcessorGroups");
+  EXPECT_NE(flag, nullptr) << "Expected UseAllWindowsProcessorGroups product flag to be available";
+
   int processors = os::processor_count();
   EXPECT_GT(processors, 0) << "Expected at least 1 processor";
 
   int active_processors = os::active_processor_count();
   EXPECT_GT(active_processors, 0) << "Expected at least 1 active processor";
 
   bool schedules_all_processor_groups = os::win32::is_windows_11_or_greater() || os::win32::is_windows_server_2022_or_greater();
-  if (schedules_all_processor_groups) {
+  if (schedules_all_processor_groups && UseAllWindowsProcessorGroups) {
     EXPECT_EQ(active_processors, processors) << "Expected all processors to be active";
   } else {
     // active_processors should be at most the number of processors in 1 Windows processor group.

test/hotspot/jtreg/TEST.groups

@@ -145,6 +145,7 @@ tier1_common = \
   gtest/MetaspaceGtests.java \
   gtest/LargePageGtests.java \
   gtest/NMTGtests.java \
+  gtest/WindowsProcessorGroups.java
 
 tier1_compiler = \
   :tier1_compiler_1 \

test/hotspot/jtreg/gtest/WindowsProcessorGroups.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+/*
+ * This runs the os related gtests on Windows with all processor groups enabled.
+ */
+
+/* @test id=use-all-windows-processor-groups
+ * @summary Run gtests with all Windows processor groups enabled
+ * @requires os.family == "windows"
+ * @run main/native GTestWrapper --gtest_filter=os* -XX:+UseAllWindowsProcessorGroups
+ */