RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v29]

[Markus Grönlund]

On Mon, 2 Jun 2025 13:50:49 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 one additional commit since the last revision:
> 
>   Fix bug related to async stack walking

src/hotspot/share/jfr/jfr.inline.hpp line 41:

> 39: inline void Jfr::check_and_process_sample_request(JavaThread* jt) {
> 40:   JfrThreadLocal* tl = jt->jfr_thread_local();
> 41:   bool has_cpu_time_sample_request = tl->has_cpu_time_jfr_requests();

Why this change?

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 191:

> 189:   void sample_thread(JfrSampleRequest& request, void* ucontext, JavaThread* jt, JfrThreadLocal* tl);
> 190: 
> 191:   // process the queues for all threads that are in native state (and requested to be sampled)

"requested to be processed" I guess.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 270:

> 268: void JfrCPUTimeThreadSampler::enroll() {
> 269:   if (Atomic::cmpxchg(&_disenrolled, true, false)) {
> 270:     log_info(jfr)("Enrolling CPU thread sampler");

log_trace, please.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 279:

> 277: void JfrCPUTimeThreadSampler::disenroll() {
> 278:   if (!Atomic::cmpxchg(&_disenrolled, false, true)) {
> 279:     log_info(jfr)("Disenrolling CPU thread sampler");

log_trace, please.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121414317
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121416556
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121426574
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121428073