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/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.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121391177