RFR: 8315149: Add hsperf counters for CPU time of internal GC threads [v53]

[Jonathan Joo]

On Fri, 1 Dec 2023 14:42:22 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> I would say it depends on the use-case and here when switching to use static functions to use the instance it felt more like an all-static class. I agree that it would be nice to avoid the additional memory usage if `UsePerfData` is `false` so I'm ok with keeping the instance if we add that.
>
>> It is easier to control the initialization order and timing of an on-heap singleton object than statics.
> 
> It's generally true, but the init of CPUTimeCounters is not sensitive to ordering.
> 
>> This could save some memory when UsePerfData is false.
> 
> True, but the mem savings will be marginal at most, `PerfCounter* _cpu_time_counters[static_cast<int>(CPUTimeGroups::CPUTimeType::COUNT)];` will be 8 * ~12 = ~96 bytes (including future cpu-time-type enums).
> 
> (I don't have a strong preference here; however, I'd like to make the pros and cons explicit.)

Added the check in the initializer

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PR Review Comment: https://git.openjdk.org/jdk/pull/15082#discussion_r1412749097