8373625: CPUTimeCounters creates a total counter for unsupported GCs

[JonasNorlinder]

CPUTimeCounters unconditionally creates CPUTimeGroups::CPUTimeType::gc_total. Since only Parallel and G1 are supported by this framework/class, this leads to publishing a counter that always resolves to 0. This may be contradictory for an end-user especially so as we now support logging GC CPU time for any GC inside Hotspot. For an example using -XX:+UseZGC -Xlog:cpu we get

[7.907s][info][cpu] === CPU time Statistics =============================================================
[7.907s][info][cpu]                                                                             CPUs
[7.907s][info][cpu]                                                                s       %  utilized
[7.907s][info][cpu]    Process
[7.907s][info][cpu]      Total                                              186.9562  100.00      23.6
[7.907s][info][cpu]      Garbage Collection                                   0.6700    0.36       0.1
[7.907s][info][cpu]        GC Threads                                         0.6692    0.36       0.1
[7.907s][info][cpu]        VM Thread                                          0.0008    0.00       0.0
[7.907s][info][cpu] =====================================================================================

But jcmd $(pgrep -n java) PerfCounter.print | grep -E "sun.threads.total_gc_cpu_time" prints: sun.threads.total_gc_cpu_time=0.

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• JDK-8373625: CPUTimeCounters creates a total counter for unsupported GCs (Bug - P4)

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/label add hotspot-gc serviceability

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