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

[Johannes Bechberger]

On Mon, 2 Jun 2025 14:57:47 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> 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?

So I don't read the ` tl->has_cpu_time_jfr_requests()` twice on the hot-path

> src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 349:
> 
>> 347:   const frame top_frame = thread->last_frame();
>> 348:   bool in_continuation = is_in_continuation(top_frame, thread);
>> 349:   for (u4 i = 0; i < queue.size(); i++) {
> 
> Realized this drainage is entirely wrong!
> 
> You are not using the sample requests in the queue to build individual stack traces for events; instead, you are using the same top frame (the last Java frame) for all of them.

Can I export compute_top_frame and use it here?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121424752
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121413413