8373625: CPUTimeCounters creates a total counter for unsupported GCs

[jyma22]

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.

Testing: passed tier1-4

---

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• JDK-8373625 needs maintainer approval

Issue

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

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[openjdk]

This backport pull request has now been updated with issue from the original commit.

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⚠️ @jyma22 This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[mlbridge]

Webrevs

• 00: Full (40040756)

[jyma22]

/approval request Backporting this patch fixes the misleading GC CPU time counter issue where sun.threads.total_gc_cpu_time always reports 0 for non-G1/Parallel collectors. The change conditionally creates the gc_total counter only when UseG1GC or UseParallelGC is enabled, preventing contradictory metrics when using other collectors like ZGC that report GC CPU time through logging but not through this counter framework.

Patch applies cleanly to 25u.

Included test passes. Ran tier1-4 with no regressions observed.

[openjdk]

@jyma22
8373625: The approval request has been created successfully.

[GoeLin]

HI @jyma22
please backport to 26 first. Maybe refer to next release of 25 as this is brand new.
Removing the label for now.