--- a/hotspot/src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp	Fri Dec 16 11:40:00 2011 -0800
+++ b/hotspot/src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp	Mon Dec 19 10:02:05 2011 -0800
@@ -672,15 +672,20 @@
 }
 
 jlong PSMarkSweep::millis_since_last_gc() {
-  jlong ret_val = os::javaTimeMillis() - _time_of_last_gc;
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
+  jlong ret_val = now - _time_of_last_gc;
   // XXX See note in genCollectedHeap::millis_since_last_gc().
   if (ret_val < 0) {
-    NOT_PRODUCT(warning("time warp: %d", ret_val);)
+    NOT_PRODUCT(warning("time warp: "INT64_FORMAT, ret_val);)
     return 0;
   }
   return ret_val;
 }
 
 void PSMarkSweep::reset_millis_since_last_gc() {
-  _time_of_last_gc = os::javaTimeMillis();
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 }