RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v42]

[Markus Grönlund]

On Tue, 3 Jun 2025 14:09:29 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:
> 
>   Rename autoadapt

src/hotspot/share/jfr/periodic/sampling/jfrThreadSampling.cpp line 360:

> 358:   tl->set_do_async_processing_of_cpu_time_jfr_requests(false);
> 359:   if (lock) {
> 360:     tl->acquire_cpu_time_jfr_dequeue_lock();

This is your synchronization point on return from native code, which is effectively a spinlock. This can cause problems when a large number of threads are being processed by the "do_async_processing" request call.

We should fix this as a bug after integration (use a proper Monitor as a synchronization point).

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2124997140