--- old/src/hotspot/share/gc/g1/g1Analytics.cpp	2020-05-18 10:29:16.219435250 +0200
+++ new/src/hotspot/share/gc/g1/g1Analytics.cpp	2020-05-18 10:29:16.131433384 +0200
@@ -149,18 +149,14 @@
   _alloc_rate_ms_seq->add(alloc_rate);
 }
 
-void G1Analytics::compute_pause_time_ratio(double interval_ms, double pause_time_ms) {
-  _long_term_pause_time_ratio = _recent_gc_times_ms->sum() / interval_ms;
-  // Filter out nonsensical results due to bad input.
+void G1Analytics::compute_pause_time_ratios(double end_time_sec, double pause_time_ms) {
+  double long_interval_ms = (end_time_sec - oldest_known_gc_end_time_sec()) * 1000.0;
+  _long_term_pause_time_ratio = _recent_gc_times_ms->sum() / long_interval_ms;
   _long_term_pause_time_ratio = clamp(_long_term_pause_time_ratio, 0.0, 1.0);
 
-  // Compute the ratio of just this last pause time to the entire time range stored
-  // in the vectors. Comparing this pause to the entire range, rather than only the
-  // most recent interval, has the effect of smoothing over a possible transient 'burst'
-  // of more frequent pauses that don't really reflect a change in heap occupancy.
-  // This reduces the likelihood of a needless heap expansion being triggered.
-  _short_term_pause_time_ratio =
-    (pause_time_ms * _recent_prev_end_times_for_all_gcs_sec->num()) / interval_ms;
+  double short_interval_ms = (end_time_sec - most_recent_gc_end_time_sec()) * 1000.0;
+  _short_term_pause_time_ratio = pause_time_ms / short_interval_ms;
+  _short_term_pause_time_ratio = clamp(_short_term_pause_time_ratio, 0.0, 1.0);
 }
 
 void G1Analytics::report_concurrent_refine_rate_ms(double cards_per_ms) {
@@ -311,10 +307,14 @@
   return predict_size(_pending_cards_seq);
 }
 
-double G1Analytics::last_known_gc_end_time_sec() const {
+double G1Analytics::oldest_known_gc_end_time_sec() const {
   return _recent_prev_end_times_for_all_gcs_sec->oldest();
 }
 
+double G1Analytics::most_recent_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);
--- old/src/hotspot/share/gc/g1/g1Analytics.hpp	2020-05-18 10:29:16.659444579 +0200
+++ new/src/hotspot/share/gc/g1/g1Analytics.hpp	2020-05-18 10:29:16.579442883 +0200
@@ -88,6 +88,9 @@
   size_t predict_size(TruncatedSeq const* seq) const;
   double predict_zero_bounded(TruncatedSeq const* seq) const;
 
+  double oldest_known_gc_end_time_sec() const;
+  double most_recent_gc_end_time_sec() const;
+
 public:
   G1Analytics(const G1Predictions* predictor);
 
@@ -160,9 +163,7 @@
 
   // Add a new GC of the given duration and end time to the record.
   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 last_known_gc_end_time_sec() const;
+  void compute_pause_time_ratios(double end_time_sec, double pause_time_ms);
 };
 
 #endif // SHARE_GC_G1_G1ANALYTICS_HPP
--- old/src/hotspot/share/gc/g1/g1Policy.cpp	2020-05-18 10:29:17.083453568 +0200
+++ new/src/hotspot/share/gc/g1/g1Policy.cpp	2020-05-18 10:29:17.007451960 +0200
@@ -118,6 +118,9 @@
   // We may immediately start allocating regions and placing them on the
   // collection set list. Initialize the per-collection set info
   _collection_set->start_incremental_building();
+
+  double now = os::elapsedTime();
+  _analytics->update_recent_gc_times(now, 0.0);
 }
 
 void G1Policy::note_gc_start() {
@@ -669,10 +672,8 @@
     double alloc_rate_ms = (double) regions_allocated / app_time_ms;
     _analytics->report_alloc_rate_ms(alloc_rate_ms);
 
-    double interval_ms =
-      (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
+    _analytics->compute_pause_time_ratios(end_time_sec, pause_time_ms);
     _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
-    _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
   }
 
   if (collector_state()->in_young_gc_before_mixed()) {