RFR: 8336742: Shenandoah: Add more verbose logging/stats for mark termination attempts [v2]

[Neethu Prasad]

> **Notes**
> This PR adds the following
> 1.  info logging on number of SATB flush attempts
> 2. total time spend on handshaking all threads requesting them to flush their SATB buffers.
> 
> As suggested by William in [JDK-8336742 ](https://bugs.openjdk.org/browse/JDK-83367420), we can use handshake logging to get time spend and other stats for each handshake.
> 
> [4.515s][info][handshake   ] Handshake "Shenandoah Flush SATB Handshake", Targeted threads: 1036, Executed by requesting thread: 1035, Total completion time: 597004 ns
> [4.517s][info][handshake   ] Handshake "Shenandoah Flush SATB Handshake", Targeted threads: 1036, Executed by requesting thread: 1033, Total completion time: 207402 ns
> 
> 
> **Testing**
> 1. tier1, tier2 and hotspot_gc_shenandoah tests.
> 2. **-Xlog:gc+stats=info**
> 
> 
> [4.058s][info][gc,stats    ] Concurrent Marking             =    0.080 s (a =     5351 us) (n =    15) (lvls, us =     4746,     5000,     5156,     5684,     5988)
> [4.058s][info][gc,stats    ]   SATB Flush Rendezvous        =    0.013 s (a =      860 us) (n =    15) (lvls, us =      764,      814,      836,      885,      961)
> [4.058s][info][gc,stats    ] Pause Final Mark (G)           =    0.058 s (a =     3839 us) (n =    15) (lvls, us =     3047,     3320,     3867,     4121,     4930)
> [4.058s][info][gc,stats    ] Pause Final Mark (N)           =    0.054 s (a =     3592 us) (n =    15) (lvls, us =     2812,     3047,     3574,     3887,     4597)
> [4.058s][info][gc,stats    ]   Finish Mark                  =    0.028 s (a =     1843 us) (n =    15) (lvls, us =     1602,     1641,     1816,     1934,     2045)
> [4.058s][info][gc,stats    ]   Update Region States         =    0.006 s (a =      386 us) (n =    15) (lvls, us =      375,      375,      381,      389,      413)
> [4.058s][info][gc,stats    ]   Choose Collection Set        =    0.018 s (a =     1186 us) (n =    15) (lvls, us =      609,      619,     1309,     1387,     2109)
> [4.058s][info][gc,stats    ]   Rebuild Free Set             =    0.001 s (a =       43 us) (n =    15) (lvls, us =       40,       41,       42,       43,       53)
> [4.058s][info][gc,stats    ] Concurrent Weak References     =    0.007 s (a =      452 us) (n =    15) (lvls, us =      420,      438,      443,      455,      487)
> 
> 
> on app termination
> 
> 
> [5.299s][info][gc,stats] GC STATISTICS:
> [5.299s][info][gc,stats]   "(G)" (gross) pauses include VM time: time to notify and block threads, do the pre-
> [5.299s][info][gc,stats]         and post-safepoint housekee...

Neethu Prasad has updated the pull request incrementally with one additional commit since the last revision:

  ShenandoahTimingsTracker to support aggregation of cycle times

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/20318/files
  - new: https://git.openjdk.org/jdk/pull/20318/files/7c3d4a84..6e7fdd5e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20318&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20318&range=00-01

  Stats: 31 lines in 5 files changed: 9 ins; 6 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/20318.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20318/head:pull/20318

PR: https://git.openjdk.org/jdk/pull/20318