--- a/hotspot/src/share/vm/gc_implementation/g1/concurrentG1Refine.cpp	Fri Sep 26 01:40:31 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/concurrentG1Refine.cpp	Sat Sep 27 15:11:41 2014 +0200
@@ -128,9 +128,7 @@
 }
 
 uint ConcurrentG1Refine::thread_num() {
-  uint n_threads = (G1ConcRefinementThreads > 0) ? G1ConcRefinementThreads
-                                                : ParallelGCThreads;
-  return MAX2<uint>(n_threads, 1);
+  return G1ConcRefinementThreads;
 }
 
 void ConcurrentG1Refine::print_worker_threads_on(outputStream* st) const {

--- a/hotspot/src/share/vm/runtime/arguments.cpp	Fri Sep 26 01:40:31 2014 -0700
+++ b/hotspot/src/share/vm/runtime/arguments.cpp	Sat Sep 27 15:11:41 2014 +0200
@@ -1697,6 +1697,12 @@
                      Abstract_VM_Version::parallel_worker_threads());
   }
 
+#if INCLUDE_ALL_GCS
+  if (G1ConcRefinementThreads == 0) {
+    FLAG_SET_DEFAULT(G1ConcRefinementThreads, ParallelGCThreads);
+  }
+#endif
+
   // MarkStackSize will be set (if it hasn't been set by the user)
   // when concurrent marking is initialized.
   // Its value will be based upon the number of parallel marking threads.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/gc/arguments/TestG1ConcRefinementThreads.java	Sat Sep 27 15:11:41 2014 +0200
@@ -0,0 +1,97 @@
+/*
+* Copyright (c) 2014, 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.
+*/
+
+/*
+ * @test TestG1ConcRefinementThreads
+ * @key gc
+ * @bug 8047976
+ * @summary Tests argument processing for G1ConcRefinementThreads
+ * @library /testlibrary
+ */
+
+import com.oracle.java.testlibrary.*;
+import java.util.*;
+import java.util.regex.*;
+
+public class TestG1ConcRefinementThreads {
+
+  static final int AUTO_SELECT_THREADS_COUNT = 0;
+  static final int PASSED_THREADS_COUNT = 11;
+
+  public static void main(String args[]) throws Exception {
+    // default case
+    runG1ConcRefinementThreadsTest(
+        new String[]{}, // automatically selected
+        AUTO_SELECT_THREADS_COUNT /* use default setting */);
+
+    // zero setting case
+    runG1ConcRefinementThreadsTest(
+        new String[]{"-XX:G1ConcRefinementThreads=0"}, // automatically selected
+        AUTO_SELECT_THREADS_COUNT /* set to zero */);
+
+    // non-zero sestting case
+    runG1ConcRefinementThreadsTest(
+        new String[]{"-XX:G1ConcRefinementThreads="+Integer.toString(PASSED_THREADS_COUNT)},
+        PASSED_THREADS_COUNT);
+  }
+
+  private static void runG1ConcRefinementThreadsTest(String[] passedOpts,
+          int expectedValue) throws Exception {
+    List<String> vmOpts = new ArrayList<>();
+    if (passedOpts.length > 0) {
+      Collections.addAll(vmOpts, passedOpts);
+    }
+    Collections.addAll(vmOpts, "-XX:+UseG1GC", "-XX:+PrintFlagsFinal", "-version");
+
+    ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(vmOpts.toArray(new String[vmOpts.size()]));
+    OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+    output.shouldHaveExitValue(0);
+    String stdout = output.getStdout();
+    checkG1ConcRefinementThreadsConsistency(stdout, expectedValue);
+  }
+
+  private static void checkG1ConcRefinementThreadsConsistency(String output, int expectedValue) {
+    int actualValue = getIntValue("G1ConcRefinementThreads", output);
+
+    if (expectedValue == 0) {
+      // If expectedValue is automatically selected, set it same as ParallelGCThreads.
+      expectedValue = getIntValue("ParallelGCThreads", output);
+    }
+
+    if (expectedValue != actualValue) {
+      throw new RuntimeException(
+            "Actual G1ConcRefinementThreads(" + Integer.toString(actualValue)
+            + ") is not equal to expected value(" + Integer.toString(expectedValue) + ")");
+    }
+  }
+
+  public static int getIntValue(String flag, String where) {
+    Matcher m = Pattern.compile(flag + "\\s+:?=\\s+\\d+").matcher(where);
+    if (!m.find()) {
+      throw new RuntimeException("Could not find value for flag " + flag + " in output string");
+    }
+    String match = m.group();
+    return Integer.parseInt(match.substring(match.lastIndexOf(" ") + 1, match.length()));
+  }
+}