RFR: 8364638: Refactor and make accumulated GC CPU time code generic [v9]

[Stefan Johansson]

On Mon, 18 Aug 2025 14:02:48 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:
>> 
>> 
>> [71.425s][info][cpu   ] === CPU time Statistics =============================================================
>> [71.425s][info][cpu   ]                                                                             CPUs
>> [71.425s][info][cpu   ]                                                                s       %  utilized
>> [71.425s][info][cpu   ]    Process
>> [71.425s][info][cpu   ]      Total                                             1616.3627  100.00      22.6
>> [71.425s][info][cpu   ]      VM Thread                                            5.2992    0.33       0.1
>> [71.425s][info][cpu   ]      Garbage Collection                                  83.7322    5.18       1.2
>> [71.425s][info][cpu   ]        GC Threads                                        82.7671    5.12       1.2
>> [71.425s][info][cpu   ]        VM Thread                                          0.9651    0.06       0.0
>> [71.425s][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:
> 
>   Fix indentation

Just some minor things that you can fix before integrating. Otherwise I think this looks good.

src/hotspot/share/gc/shared/collectedHeap.cpp line 59:

> 57: #include "runtime/threadSMR.hpp"
> 58: #include "runtime/vmThread.hpp"
> 59: #include "services/cpuTimeUsage.hpp"

Can be removed now.

src/hotspot/share/gc/shared/collectedHeap.hpp line 434:

> 432:   void print_relative_to_gc(GCWhen::Type when) const;
> 433: 
> 434:   void log_cpu_time() const;

This has moved to `Universe` and can be removed.

-------------

Marked as reviewed by sjohanss (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26621#pullrequestreview-3131175838
PR Review Comment: https://git.openjdk.org/jdk/pull/26621#discussion_r2284454451
PR Review Comment: https://git.openjdk.org/jdk/pull/26621#discussion_r2284450710