Allow to override default behavior on Windows 11+

src/coreclr/inc/configuration.h

@@ -33,7 +33,9 @@ class Configuration
     // Unfortunately our traditional config system insists on interpreting numbers as 32-bit so interpret the config
     // in the traditional way separately if you need to.
     //
-    // Returns value for name if found in config.
+    // Returns (in priority order):
+    //    - The value of the ConfigurationKnob (searched by name) if it's set (performs a _wcstoui64)
+    //    - The default value passed in
     static ULONGLONG GetKnobULONGLONGValue(LPCWSTR name, ULONGLONG defaultValue);
 
     // Returns (in priority order):
@@ -48,11 +50,17 @@ class Configuration
     static LPCWSTR GetKnobStringValue(LPCWSTR name);
 
     // Returns (in priority order):
-    //    - The value of the ConfigDWORDInfo if it's set (1 is true, anything else is false)
+    //    - The value of the ConfigDWORDInfo if it's set (0 is false, anything else is true)
     //    - The value of the ConfigurationKnob (searched by name) if it's set (performs a wcscmp with "true").
-    //    - The default set in the ConfigDWORDInfo (1 is true, anything else is false)
+    //    - The default set in the ConfigDWORDInfo (0 is false, anything else is true)
     static bool GetKnobBooleanValue(LPCWSTR name, const CLRConfig::ConfigDWORDInfo& dwordInfo);
 
+    // Returns (in priority order):
+    //    - The value of the ConfigDWORDInfo if it's set (0 is false, anything else is true)
+    //    - The value of the ConfigurationKnob (searched by name) if it's set (performs a wcscmp with "true").
+    //    - The default value passed in
+    static bool GetKnobBooleanValue(LPCWSTR name, const CLRConfig::ConfigDWORDInfo& dwordInfo, bool defaultValue);
+
     // Returns (in priority order):
     //    - The value of the ConfigurationKnob (searched by name) if it's set (performs a wcscmp with "true").
     //    - The default value passed in

src/coreclr/utilcode/configuration.cpp

@@ -123,6 +123,18 @@ bool Configuration::GetKnobBooleanValue(LPCWSTR name, const CLRConfig::ConfigDWO
     return (legacyValue != 0);
 }
 
+bool Configuration::GetKnobBooleanValue(LPCWSTR name, const CLRConfig::ConfigDWORDInfo& dwordInfo, bool defaultValue)
+{
+    bool returnedDefaultValue;
+    DWORD legacyValue = CLRConfig::GetConfigValue(dwordInfo, &returnedDefaultValue);
+    if (!returnedDefaultValue)
+    {
+        return (legacyValue != 0);
+    }
+
+    return GetKnobBooleanValue(name, defaultValue);
+}
+
 bool Configuration::GetKnobBooleanValue(LPCWSTR name, bool defaultValue)
 {
     LPCWSTR knobValue = GetConfigurationValue(name);

src/coreclr/utilcode/util.cpp

@@ -762,13 +762,14 @@ DWORD LCM(DWORD u, DWORD v)
 #if !defined(FEATURE_NATIVEAOT) && (defined(TARGET_AMD64) || defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64))
     USHORT groupCount = 0;
 
-    // Starting with Windows 11 and Windows Server 2022, a process is no longer restricted to a single processor group
-    // by default. Use all processor groups if the process is not affinitized to a single one.
+    // On Windows 11+ and Windows Server 2022+, a process is no longer restricted to a single processor group by default.
+    // If more than one processor group is available to the process (a non-affinitized process on Windows 11+),
+    // default to using multiple processor groups; otherwise, default to using a single processor group. This default
+    // behavior may be overridden by the configuration values below.
     if (GetProcessGroupAffinity(GetCurrentProcess(), &groupCount, NULL) || GetLastError() != ERROR_INSUFFICIENT_BUFFER)
         groupCount = 1;
 
-    BOOL enableGCCPUGroups = groupCount > 1 ||
-        Configuration::GetKnobBooleanValue(W("System.GC.CpuGroup"), CLRConfig::EXTERNAL_GCCpuGroup);
+    BOOL enableGCCPUGroups = Configuration::GetKnobBooleanValue(W("System.GC.CpuGroup"), CLRConfig::EXTERNAL_GCCpuGroup, groupCount > 1);
 
     if (!enableGCCPUGroups)
         return;
@@ -780,7 +781,7 @@ DWORD LCM(DWORD u, DWORD v)
     if (m_nGroups > 1)
     {
         m_enableGCCPUGroups = TRUE;
-        m_threadUseAllCpuGroups = groupCount > 1 || CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_Thread_UseAllCpuGroups) != 0;
+        m_threadUseAllCpuGroups = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_Thread_UseAllCpuGroups, groupCount > 1) != 0;
         m_threadAssignCpuGroups = CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_Thread_AssignCpuGroups) != 0;
 
         // Save the processor group affinity of the initial thread