8346568: G1: Other time can be negative

[sangheon]

Other time described in this bug is displayed at G1GCPhaseTimes::print_other(total_measured_time - sum_of_sub_phases). And the value can be negative for 3 reasons.

1. Different scope of measurement
   • 3 variables is out of scope from total_measured_time. Those used for wait-root-region-scan, verify-before/after.
     (_root_region_scan_wait_time_ms, _cur_verify_before_time_ms and _cur_verify_after_time_ms)
   • Changed not to be included in sum_of_sub_phases.
   • One may want to include them in total_measured_time but I think it is better to be addressed in a separate ticket.
2. Duplicated measurement
   • Initial and optional evacuation time include nmethod-cleanup-time, so separated them as we are already measuring them. As there is no public getter, just added cleanup time when those evacuation time are used internally.
3. Pre Concurrent task execution time
   • Sometimes the difference between the existing average time and pre-concurrent work is 2 digit milliseconds. Changed to measure exact time rather than accumulating the average value to sum_of_sub_phases and keep displaying concurrent tasks' average execution time.

Testing: tier 1 ~ 5

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• JDK-8346568: G1: Other time can be negative (Bug - P4)

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