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/jfrThreadSampling.cpp line 362:

> 360:   drain_enqueued_requests(now, tl, jt, current);
> 361: #ifdef LINUX
> 362:   if (tl->has_cpu_time_jfr_requests()) {

You are having all threads traverse over this lock, even though the cpu time sampler is disabled by default. Can it be improved?

src/hotspot/share/jfr/support/jfrThreadLocal.cpp line 604:

> 602: 
> 603: bool JfrThreadLocal::has_cpu_time_jfr_requests() {
> 604:   return Atomic::load(&_has_cpu_time_jfr_requests);

Atomic::load_acquire()

src/hotspot/share/jfr/support/jfrThreadLocal.cpp line 620:

> 618: 
> 619: bool JfrThreadLocal::wants_async_processing_of_cpu_time_jfr_requests() {
> 620:   return Atomic::load(&_do_async_processing_of_cpu_time_jfr_requests);

Atomic::load_acquire()

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119242319
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119243305
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119243393