RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v26]

[Markus Grönlund]

On Sun, 1 Jun 2025 07:26:19 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

>> This is the code for the [JEP 509: CPU Time based profiling for JFR](https://openjdk.org/jeps/509).
>> 
>> Currently tested using [this test suite](https://github.com/parttimenerd/basic-profiler-tests). This runs profiles the [Renaissance](https://renaissance.dev/) benchmark with
>> - ... different heap sizes
>> - ... different GCs
>> - ... different samplers (the standard JFR and the new CPU Time Sampler and both)
>> - ... different JFR recording durations
>> - ... different chunk-sizes
>
> Johannes Bechberger has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Refactoring
>  - Remove convoluted native trace logic

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 332:

> 330:     JavaThread* jt = tlh.list()->thread_at(i);
> 331:     JfrThreadLocal* tl = jt->jfr_thread_local();
> 332:     if (tl != nullptr && tl->wants_async_processing_of_cpu_time_jfr_requests()) {

tl is never nullptr.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 344:

> 342: 
> 343: // equals operator for JfrSampleRequest
> 344: inline bool operator==(const JfrSampleRequest& lhs, const JfrSampleRequest& rhs) {

Can be removed.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 574:

> 572: 
> 573:   if (queue.enqueue(request)) {
> 574:     tl->set_has_cpu_time_jfr_requests(true);

This should only need to be set when enqueuing the first entry.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 581:

> 579: 
> 580:   if (jt->thread_state() == _thread_in_native &&
> 581:       queue.size() > queue.capacity() * 2 / 3) {

Is this logic still valid? You are only asking for a async processing depending on the load factor of the queue?

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 586:

> 584:     JfrCPUTimeThreadSampling::trigger_async_processing_of_cpu_time_jfr_requests();
> 585:   } else {
> 586:     tl->set_do_async_processing_of_cpu_time_jfr_requests(false);

Was it true before and needed a reset?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119250661
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119250887
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119248176
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119248824
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119249381