8277137: Set OnSpinWaitInst/OnSpinWaitInstCount defaults to "isb"/1 for Arm Neoverse N1

Reviewed-by: phh, aph, ngasson

src/hotspot/cpu/aarch64/vm_version_aarch64.cpp

@@ -202,6 +202,14 @@ void VM_Version::initialize() {
     if (FLAG_IS_DEFAULT(UseSIMDForMemoryOps)) {
       FLAG_SET_DEFAULT(UseSIMDForMemoryOps, true);
     }
+
+    if (FLAG_IS_DEFAULT(OnSpinWaitInst)) {
+      FLAG_SET_DEFAULT(OnSpinWaitInst, "isb");
+    }
+
+    if (FLAG_IS_DEFAULT(OnSpinWaitInstCount)) {
+      FLAG_SET_DEFAULT(OnSpinWaitInstCount, 1);
+    }
   }
 
   if (_cpu == CPU_ARM) {

test/hotspot/jtreg/compiler/onSpinWait/TestOnSpinWaitAArch64DefaultFlags.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright Amazon.com Inc. 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.
+ */
+
+/**
+ * @test TestOnSpinWaitAArch64DefaultFlags
+ * @summary Check default values of '-XX:OnSpinWaitInst' and '-XX:OnSpinWaitInstCount' for AArch64 implementations.
+ * @bug 8277137
+ * @library /test/lib /
+ *
+ * @requires os.arch=="aarch64"
+ *
+ * @build sun.hotspot.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller sun.hotspot.WhiteBox
+ * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions
+ *                   -XX:+WhiteBoxAPI
+ *                   compiler.onSpinWait.TestOnSpinWaitAArch64DefaultFlags
+ */
+
+package compiler.onSpinWait;
+
+import java.util.Iterator;
+import java.util.List;
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.process.ProcessTools;
+import sun.hotspot.cpuinfo.CPUInfo;
+
+public class TestOnSpinWaitAArch64DefaultFlags {
+    private static boolean isCPUModelNeoverseN1(String cpuModel) {
+        return cpuModel.contains("0xd0c");
+    }
+
+    private static void checkFinalFlagsEqualTo(ProcessBuilder pb, String expectedOnSpinWaitInstValue, String expectedOnSpinWaitInstCountValue) throws Exception {
+        OutputAnalyzer analyzer = new OutputAnalyzer(pb.start());
+        analyzer.shouldHaveExitValue(0);
+
+        Iterator<String> iter = analyzer.asLines().listIterator();
+        String line = null;
+        boolean hasExpectedOnSpinWaitInstValue = false;
+        boolean hasExpectedOnSpinWaitInstCountValue = false;
+        while (iter.hasNext()) {
+            line = iter.next();
+            if (!hasExpectedOnSpinWaitInstValue && line.contains("ccstr OnSpinWaitInst")) {
+                hasExpectedOnSpinWaitInstValue = line.contains("= " + expectedOnSpinWaitInstValue);
+            }
+
+            if (!hasExpectedOnSpinWaitInstCountValue && line.contains("uint OnSpinWaitInstCount")) {
+                hasExpectedOnSpinWaitInstCountValue = line.contains("= " + expectedOnSpinWaitInstCountValue);
+            }
+        }
+        if (!hasExpectedOnSpinWaitInstValue) {
+            System.out.println(analyzer.getOutput());
+            throw new RuntimeException("OnSpinWaitInst with the expected value '" + expectedOnSpinWaitInstValue + "' not found.");
+        }
+        if (!hasExpectedOnSpinWaitInstCountValue) {
+            System.out.println(analyzer.getOutput());
+            throw new RuntimeException("OnSpinWaitInstCount with the expected value '" + expectedOnSpinWaitInstCountValue + "' not found.");
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        List<String> cpuFeatures = CPUInfo.getFeatures();
+        if (cpuFeatures.isEmpty()) {
+            System.out.println("Skip because no CPU features are available.");
+            return;
+        }
+
+        final String cpuModel = cpuFeatures.get(0);
+
+        if (isCPUModelNeoverseN1(cpuModel)) {
+            checkFinalFlagsEqualTo(ProcessTools.createJavaProcessBuilder("-XX:+PrintFlagsFinal", "-version"), "isb", "1");
+            checkFinalFlagsEqualTo(ProcessTools.createJavaProcessBuilder("-XX:+UnlockDiagnosticVMOptions", "-XX:OnSpinWaitInstCount=2", "-XX:+PrintFlagsFinal", "-version"),
+                "isb", "2");
+        } else {
+            System.out.println("Skip because no defaults for CPU model: " + cpuModel);
+        }
+    }
+}