Add a flag to return 0 if only one data point has been recorded

Currently, getProcessCpuLoad() and getSystemCpuLoad() return -1 if only
one data point has been recorded. A compatibility flag
-XX:[+/-]CpuLoadCompatibility is added to match the behaviour of the RI,
which is to return 0.

Fixes: #13389
Related: eclipse-omr/omr#7189

Signed-off-by: Gengchen Tuo <[email protected]>

jcl/src/jdk.management/share/classes/com/ibm/lang/management/internal/ExtendedOperatingSystemMXBeanImpl.java

@@ -245,6 +245,12 @@ public final String getHardwareModel() throws UnsupportedOperationException {
 	/* Returns the number of CPU's online at this very moment. */
 	private native int getOnlineProcessorsImpl();
 
+	/**
+	 * Check if the CpuLoadCompatibility flag is set.
+	 * @return if the CpuLoadCompatibility flag is set
+	 */
+	private static native boolean hasCpuLoadCompatibilityFlag();
+
 	/**
 	 * {@inheritDoc}
 	 */
@@ -263,16 +269,21 @@ public final synchronized double getProcessCpuLoad() {
 		}
 		latestCpuTime = cpuTime;
 
-		/* First call to this method should -1, since we don't have any previous
-		 * CPU times (or timestamp) to compute CPU load against.
+		/* First call to this method returns 0 to match the behaviour of the RI.
+		 * If the CpuLoadCompatibility flag is set, the bahaviour is reverted to
+		 * return -1 for compatibility.
 		 */
 		if (-1 == oldTime) {
 			/* Save current counters; next invocation onwards, we use these to
 			 * compute CPU loads.
 			 */
 			oldTime = interimTime = latestTime;
 			oldCpuTime = interimCpuTime = latestCpuTime;
-			return CpuLoadCalculationConstants.ERROR_VALUE;
+			if (hasCpuLoadCompatibilityFlag()) {
+				return 0;
+			} else {
+				return CpuLoadCalculationConstants.ERROR_VALUE;
+			}
 		}
 
 		/* If a sufficiently long interval has elapsed since last sampling, calculate using

runtime/jcl/common/extendedosmbean.c

@@ -518,6 +518,20 @@ Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getHardw
 	return (NULL == str) ? NULL : (*env)->NewStringUTF(env, str);
 }
 
+/**
+ * Check if the CpuLoadCompatibility flag is set.
+ *
+ * @param env instance of JNIEnv
+ * @param unusedClass
+ *
+ * @return if the CpuLoadCompatibility flag is set
+ */
+jboolean JNICALL
+Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_hasCpuLoadCompatibilityFlag(JNIEnv *env, jclass unusedClass) {
+	J9JavaVM *vm = ((J9VMThread *)env)->javaVM;
+	return J9_ARE_ALL_BITS_SET(vm->extendedRuntimeFlags2, J9_EXTENDED_RUNTIME2_CPU_LOAD_COMPATIBILITY);
+}
+
 /**
  * Returns the maximum number of file descriptors that can be opened in a process.
  *

runtime/jcl/common/mgmtosext.c

@@ -83,6 +83,8 @@ jdouble JNICALL
 Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getSystemCpuLoadImpl(JNIEnv *env, jobject instance) {
 	PORT_ACCESS_FROM_ENV(env);
 	OMRPORT_ACCESS_FROM_J9PORT(PORTLIB);
+
+	J9JavaVM *vm = ((J9VMThread *)env)->javaVM;
 	double cpuLoad = 0.0;
 
 	intptr_t portLibraryStatus = omrsysinfo_get_CPU_load(&cpuLoad);
@@ -95,6 +97,12 @@ Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getSyste
 		case OMRPORT_ERROR_SYSINFO_NOT_SUPPORTED:
 			portLibraryStatus = -3;
 			break;
+		case OMRPORT_ERROR_INSUFFICIENT_DATA:
+			portLibraryStatus =
+				J9_ARE_ALL_BITS_SET(vm->extendedRuntimeFlags2, J9_EXTENDED_RUNTIME2_CPU_LOAD_COMPATIBILITY)
+				? 0
+				: -1;
+			break;
 		default:
 			portLibraryStatus = OMRPORT_ERROR_OPFAILED;
 			break;

runtime/jcl/exports.cmake

@@ -228,6 +228,7 @@ omr_add_exports(jclse
 	Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getSystemCpuLoadImpl
 	Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getTotalPhysicalMemoryImpl
 	Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getTotalProcessorUsageImpl
+	Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_hasCpuLoadCompatibilityFlag
 	Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_isDLPAREnabled
 	Java_com_ibm_lang_management_internal_ExtendedRuntimeMXBeanImpl_getVMIdleStateImpl
 	Java_com_ibm_lang_management_internal_JvmCpuMonitor_getThreadCategoryImpl

runtime/jcl/uma/se7_exports.xml

@@ -67,6 +67,7 @@
 	<export name="Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getMemoryUsageImpl" />
 	<export name="Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getOnlineProcessorsImpl" />
 	<export name="Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getHardwareModelImpl" />
+	<export name="Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_hasCpuLoadCompatibilityFlag" />
 	<export name="Java_com_ibm_lang_management_internal_JvmCpuMonitor_getThreadsCpuUsageImpl" />
 	<export name="Java_com_ibm_lang_management_internal_JvmCpuMonitor_setThreadCategoryImpl" />
 	<export name="Java_com_ibm_lang_management_internal_JvmCpuMonitor_getThreadCategoryImpl" />

runtime/oti/j9consts.h

@@ -361,7 +361,7 @@ extern "C" {
 #define J9_EXTENDED_RUNTIME2_USE_CONTAINER_SUPPORT 0x200000
 #define J9_EXTENDED_RUNTIME2_SHOW_CARRIER_FRAMES 0x400000
 #define J9_EXTENDED_RUNTIME2_CRIU_SINGLE_THROW_BLOCKING_EXCEPTIONS 0x800000
-#define J9_EXTENDED_RUNTIME2_UNUSED_0x1000000 0x1000000
+#define J9_EXTENDED_RUNTIME2_CPU_LOAD_COMPATIBILITY 0x1000000
 
 #define J9_OBJECT_HEADER_AGE_DEFAULT 0xA /* OBJECT_HEADER_AGE_DEFAULT */
 #define J9_OBJECT_HEADER_SHAPE_MASK 0xE /* OBJECT_HEADER_SHAPE_MASK */

runtime/oti/jclprots.h

@@ -1166,6 +1166,8 @@ Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getOnlin
 jstring JNICALL
 Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_getHardwareModelImpl(JNIEnv *env, jobject obj);
 
+jboolean JNICALL
+Java_com_ibm_lang_management_internal_ExtendedOperatingSystemMXBeanImpl_hasCpuLoadCompatibilityFlag(JNIEnv *env, jclass unusedClass);
 /**
  * Returns the maximum number of file descriptors that can be opened in a process.
  *

runtime/oti/jvminit.h

@@ -417,6 +417,8 @@ enum INIT_STAGE {
 #define VMOPT_XXDISABLEENSUREHASHED "-XX:-EnsureHashed:"
 #define VMOPT_XXOPENJ9COMMANDLINEENV "-XX:+OpenJ9CommandLineEnv"
 #define VMOPT_XXNOOPENJ9COMMANDLINEENV "-XX:-OpenJ9CommandLineEnv"
+#define VMOPT_XXCPULOADCOMPATIBILITY "-XX:+CpuLoadCompatibility"
+#define VMOPT_XXNOCPULOADCOMPATIBILITY "-XX:-CpuLoadCompatibility"
 
 #if defined(J9VM_ZOS_3164_INTEROPERABILITY)
 #define VMOPT_XXENABLE3164INTEROPERABILITY "-XX:+Enable3164Interoperability"

runtime/vm/jvminit.c

@@ -4123,6 +4123,14 @@ processVMArgsFromFirstToLast(J9JavaVM * vm)
 		}
 	}
 
+	{
+		IDATA cpuLoadCompatibility = FIND_AND_CONSUME_VMARG(EXACT_MATCH, VMOPT_XXCPULOADCOMPATIBILITY , NULL);
+		IDATA noCpuLoadCompatibility = FIND_AND_CONSUME_VMARG(EXACT_MATCH, VMOPT_XXNOCPULOADCOMPATIBILITY , NULL);
+		if (cpuLoadCompatibility > noCpuLoadCompatibility) {
+			vm->extendedRuntimeFlags2 |= J9_EXTENDED_RUNTIME2_CPU_LOAD_COMPATIBILITY;
+		}
+	}
+
 	return JNI_OK;
 }