--- a/hotspot/src/share/vm/gc/g1/g1Analytics.cpp	Wed Jul 05 22:07:34 2017 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1Analytics.cpp	Fri Aug 19 17:19:47 2016 +0200
@@ -316,14 +316,10 @@
   return get_new_size_prediction(_pending_cards_seq);
 }
 
-double G1Analytics::oldest_known_gc_end_time_sec() const {
+double G1Analytics::last_known_gc_end_time_sec() const {
   return _recent_prev_end_times_for_all_gcs_sec->oldest();
 }
 
-double G1Analytics::last_known_gc_end_time_sec() const {
-  return _recent_prev_end_times_for_all_gcs_sec->last();
-}
-
 void G1Analytics::update_recent_gc_times(double end_time_sec,
                                          double pause_time_ms) {
   _recent_gc_times_ms->add(pause_time_ms);

--- a/hotspot/src/share/vm/gc/g1/g1Analytics.hpp	Wed Jul 05 22:07:34 2017 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1Analytics.hpp	Fri Aug 19 17:19:47 2016 +0200
@@ -155,7 +155,6 @@
   void update_recent_gc_times(double end_time_sec, double elapsed_ms);
   void compute_pause_time_ratio(double interval_ms, double pause_time_ms);
 
-  double oldest_known_gc_end_time_sec() const;
   double last_known_gc_end_time_sec() const;
 };
 

--- a/hotspot/src/share/vm/gc/g1/g1CollectedHeap.cpp	Wed Jul 05 22:07:34 2017 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1CollectedHeap.cpp	Fri Aug 19 17:19:47 2016 +0200
@@ -28,7 +28,6 @@
 #include "classfile/symbolTable.hpp"
 #include "code/codeCache.hpp"
 #include "code/icBuffer.hpp"
-#include "gc/g1/g1Analytics.hpp"
 #include "gc/g1/bufferingOopClosure.hpp"
 #include "gc/g1/concurrentG1Refine.hpp"
 #include "gc/g1/concurrentG1RefineThread.hpp"
@@ -2474,19 +2473,8 @@
 }
 
 jlong G1CollectedHeap::millis_since_last_gc() {
-  jlong now = os::elapsed_counter() / NANOSECS_PER_MILLISEC;
-  const G1Analytics* analytics = _g1_policy->analytics();
-  double last = analytics->last_known_gc_end_time_sec();
-  jlong ret_val = now - (last * 1000);
-  if (ret_val < 0) {
-    // See the notes in GenCollectedHeap::millis_since_last_gc()
-    // for more information about the implementation.
-    log_warning(gc)("Detected clock going backwards. "
-      "Milliseconds since last GC would be " JLONG_FORMAT
-      ". returning zero instead.", ret_val);
-    return 0;
-  }
-  return ret_val;
+  // assert(false, "NYI");
+  return 0;
 }
 
 void G1CollectedHeap::prepare_for_verify() {

--- a/hotspot/src/share/vm/gc/g1/g1DefaultPolicy.cpp	Wed Jul 05 22:07:34 2017 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1DefaultPolicy.cpp	Fri Aug 19 17:19:47 2016 +0200
@@ -604,7 +604,7 @@
     _analytics->report_alloc_rate_ms(alloc_rate_ms);
 
     double interval_ms =
-      (end_time_sec - _analytics->oldest_known_gc_end_time_sec()) * 1000.0;
+      (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
     _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
     _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
   }

--- a/hotspot/src/share/vm/gc/shared/genCollectedHeap.cpp	Wed Jul 05 22:07:34 2017 +0200
+++ b/hotspot/src/share/vm/gc/shared/genCollectedHeap.cpp	Fri Aug 19 17:19:47 2016 +0200
@@ -1256,21 +1256,21 @@
 };
 
 jlong GenCollectedHeap::millis_since_last_gc() {
-  // javaTimeNanos() is guaranteed to be monotonically non-decreasing
-  // provided the underlying platform provides such a time source
-  // (and it is bug free). So we still have to guard against getting
-  // back a time later than 'now'.
+  // We need a monotonically non-decreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
   GenTimeOfLastGCClosure tolgc_cl(now);
   // iterate over generations getting the oldest
   // time that a generation was collected
   generation_iterate(&tolgc_cl, false);
 
+  // javaTimeNanos() is guaranteed to be monotonically non-decreasing
+  // provided the underlying platform provides such a time source
+  // (and it is bug free). So we still have to guard against getting
+  // back a time later than 'now'.
   jlong retVal = now - tolgc_cl.time();
   if (retVal < 0) {
-    log_warning(gc)("Detected clock going backwards. "
-      "Milliseconds since last GC would be " JLONG_FORMAT
-      ". returning zero instead.", retVal);
+    NOT_PRODUCT(log_warning(gc)("time warp: " JLONG_FORMAT, retVal);)
     return 0;
   }
   return retVal;