RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v5]

[Markus Grönlund]

On Fri, 23 May 2025 21:20:39 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 compilation

src/hotspot/share/jfr/support/jfrThreadLocal.cpp line 548:

> 546: #ifdef LINUX
> 547: 
> 548: bool JfrThreadLocal::acquire_cpu_time_jfr_enqueue_lock() {

Can you describe the lock protocol and why a thread must lock its thread-local queue?

Is it because sampling interrupts can interleave after you have started to process a sample as part of a previous interrupt?

src/hotspot/share/jfr/support/jfrThreadLocal.hpp line 373:

> 371: #ifdef LINUX
> 372:   void set_cpu_timer(timer_t timer) {
> 373:     _has_cpu_timer = true;

Does not necessarily have to be defined in the .hpp file. Please move to .cpp.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2106156788
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2106156997