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 49:

> 47: 
> 48: static bool is_excluded(JavaThread* thread) {
> 49:   return thread->is_hidden_from_external_view() || thread->jfr_thread_local()->is_excluded();

I think I misled you saying that JfrRecorder_thread would be excluded by the above expression. That was true - but not anymore.

Our exclusion test looks like:

static inline bool is_excluded(JavaThread* jt) {
  assert(jt != nullptr, "invariant");
  return jt->is_Compiler_thread() || jt->is_hidden_from_external_view() || jt->is_JfrRecorder_thread() || jt->jfr_thread_local()->is_excluded();
}

I like you could fold jt->is_Compiler_thread() into jt->is_hidden_from_external_view() - good!.

But can you please again list the condition jt->is_JfrRecorder_thread() ? Sorry, I forgot we had removed it from being considered excluded on the JfrThreadLocal level. Thanks.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2122045043