src/hotspot/share/gc/g1/g1Policy.cpp

rev 56990 : imported patch 8228609-used-vs-copied-bytes
rev 56991 : imported patch 8228609-kbarrett-review
rev 56992 : imported patch 8227739-merge-scan-rs-update-rs-cost
rev 56993 : [mq]: 8227739-sjohanss-review

@@ -720,11 +720,15 @@
     // Update prediction for card merge; MergeRSDirtyCards includes the cards from the Eager Reclaim phase.
     size_t const total_cards_merged = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
                                       p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
                                       total_log_buffer_cards;
 
-    if (total_cards_merged > 10) {
+    // The threshold for the number of cards in a given sampling which we consider
+    // large enough so that the impact from setup and other costs is negligible.
+    size_t const CardsNumSamplingThreshold = 10;
+    
+    if (total_cards_merged > CardsNumSamplingThreshold) {
       double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) +
                                     average_time_ms(G1GCPhaseTimes::MergeRS) +
                                     average_time_ms(G1GCPhaseTimes::MergeHCC) +
                                     average_time_ms(G1GCPhaseTimes::MergeLB) +
                                     average_time_ms(G1GCPhaseTimes::OptMergeRS);

@@ -733,11 +737,11 @@
 
     // Update prediction for card scan
     size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
                                        p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
 
-    if (total_cards_scanned > 10) {
+    if (total_cards_scanned > CardsNumSamplingThreshold) {
       double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) +
                                         average_time_ms(G1GCPhaseTimes::OptScanHR);
 
       _analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned, this_pause_was_young_only);
     }