RFR (S) 8245812: Shenandoah: compute root phase parallelism

[Aleksey Shipilev]

On 5/26/20 4:40 PM, Aleksey Shipilev wrote:
> RFE:
>   https://bugs.openjdk.java.net/browse/JDK-8245812
> 
> Current gc+stats log says:
> 
> [gc,stats] All times are wall-clock times, except per-root-class counters, that are sum over
> [gc,stats] all workers. Dividing the <total> over the root stage time estimates parallelism.
> 
> But we can actually compute it ourselves:

Actually, should test for (total > 0), on the off-chance it is uninitialized:

diff -r 6a562866cbd0 src/hotspot/share/gc/shenandoah/shenandoahPhaseTimings.cpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahPhaseTimings.cpp        Tue May 26 09:44:17 2020 -0400
+++ b/src/hotspot/share/gc/shenandoah/shenandoahPhaseTimings.cpp        Tue May 26 19:49:45 2020 +0200
@@ -35,10 +35,11 @@

 #define SHENANDOAH_PHASE_NAME_FORMAT "%-28s"
 #define SHENANDOAH_S_TIME_FORMAT "%8.3lf"
 #define SHENANDOAH_US_TIME_FORMAT "%8.0lf"
 #define SHENANDOAH_US_WORKER_TIME_FORMAT "%3.0lf"
+#define SHENANDOAH_PARALLELISM_FORMAT "%4.2lf"

 #define SHENANDOAH_PHASE_DECLARE_NAME(type, title) \
   title,

 const char* ShenandoahPhaseTimings::_phase_names[] = {
@@ -227,10 +228,18 @@
   out->cr();
   for (uint i = 0; i < _num_phases; i++) {
     double v = _cycle_data[i] * 1000000.0;
     if (v > 0) {
       out->print(SHENANDOAH_PHASE_NAME_FORMAT " " SHENANDOAH_US_TIME_FORMAT " us", _phase_names[i], v);
+
+      if (is_worker_phase(Phase(i))) {
+        double total = _cycle_data[i + 1] * 1000000.0;
+        if (total > 0) {
+          out->print(", parallelism: " SHENANDOAH_PARALLELISM_FORMAT "x", total / v);
+        }
+      }
+
       if (_worker_data[i] != NULL) {
         out->print(", workers (us): ");
         for (uint c = 0; c < _max_workers; c++) {
           double tv = _worker_data[i]->get(c);
           if (tv != ShenandoahWorkerData::uninitialized()) {

-- 
Thanks,
-Aleksey