RFR: 8364638: Refactor and make accumulated GC CPU time code generic [v3]

[Daniel D. Daugherty]

On Mon, 4 Aug 2025 19:53:24 GMT, Jonas Norlinder <duke at openjdk.org> wrote:

>> Hi all,
>> 
>> This PR refactors the newly added GC CPU time code from [JDK-8359110](https://bugs.openjdk.org/browse/JDK-8359110).
>> 
>> As a stepping-stone to enable consolidation of CPU time tracking in e.g. hsperf counters and GCTraceCPUTime and to have a unified interface for tracking CPU time of various components in Hotspot this code can be refactored. This PR introduces a new interface to retrieve CPU time for various Hotspot components and it currently supports:
>> 
>> CPUTimeUsage::GC::total() // the sum of gc_threads(), vm_thread(), stringdedup()
>> 
>> CPUTimeUsage::GC::gc_threads()
>> CPUTimeUsage::GC::vm_thread()
>> CPUTimeUsage::GC::stringdedup()
>> 
>> CPUTimeUsage::Runtime::vm_thread()
>> 
>> 
>> I moved `CPUTimeUsage` to `src/hotspot/share/services` since it seemed fitting as it housed similar performance tracking code like `RuntimeService`, as this is no longer a class that is only specific to GC.
>> 
>> I also made a minor improvement in the CPU time logging during exit. Since `CPUTimeUsage` supports more components than just GC I changed the logging flag to from `gc,cpu` to `cpu` and created a detailed table:
>> 
>> 
>> [12.517s][info][cpu] === CPU time Statistics =============================================================
>> [12.517s][info][cpu]                                                                             CPUs
>> [12.517s][info][cpu]                                                                s       %  utilized
>> [12.517s][info][cpu]    Process
>> [12.517s][info][cpu]      Total                                              175.7628  100.00      14.0
>> [12.517s][info][cpu]      VM Thread                                            7.0000    3.98       0.6
>> [12.517s][info][cpu]      Garbage Collection                                  72.0000   40.96       5.8
>> [12.517s][info][cpu]        GC Threads                                        70.0000   39.83       5.6
>> [12.517s][info][cpu]        VM Thread                                          1.0000    0.57       0.1
>> [12.518s][info][cpu]        String Deduplication                               0.0000    0.00       0.0
>> [12.518s][info][cpu] =====================================================================================
>> 
>> 
>> Additionally, if CPU time retrieval fails it should not be the caller's responsibility to log warnings as this would bloat the code unnecessarily. I've noticed that `os` does log a warning for some methods if they fail so I continued on this path.
>
> Jonas Norlinder has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Prefer returning 0 over +/-inf,nan

Seems like JVM/TI folks will be interested also.

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PR Comment: https://git.openjdk.org/jdk/pull/26621#issuecomment-3152782164