RFR: Print correct message about gross times in stats

[Aleksey Shipilev]

Hi,

We should make it clear gross times are not only about TTSP, but about the
entire safepoint mechanics. Let's make it say this:

$ hg diff
diff -r 4931b832162d src/share/vm/gc/shenandoah/shenandoahCollectorPolicy.cpp
--- a/src/share/vm/gc/shenandoah/shenandoahCollectorPolicy.cpp	Fri May 12
17:06:04 2017 +0200
+++ b/src/share/vm/gc/shenandoah/shenandoahCollectorPolicy.cpp	Mon May 15
20:10:38 2017 +0200
@@ -1018,7 +1018,9 @@
 void ShenandoahCollectorPolicy::print_tracing_info(outputStream* out) {
   out->cr();
   out->print_cr("GC STATISTICS:");
-  out->print_cr("  \"(G)\" (gross) pauses include time to safepoint. \"(N)\"
(net) pauses are times spent in GC.");
+  out->print_cr("  \"(G)\" (gross) pauses include VM time: time to notify and
block threads, do the pre-");
+  out->print_cr("        and post-safepoint housekeeping. Use
-XX:+PrintSafepointStatistics to dissect.");
+  out->print_cr("  \"(N)\" (net) pauses are the times spent in the actual GC
code.");
   out->print_cr("  \"a\" is average time for each phase, look at levels to see
if average makes sense.");
   out->print_cr("  \"lvls\" are quantiles: 0%% (minimum), 25%%, 50%% (median),
75%%, 100%% (maximum).");
   out->cr();

Thanks,
-Aleksey