RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v61]

[David Holmes]

On Wed, 4 Jun 2025 19:55:55 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:
> 
>   Renaming

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 88:

> 86:       return false;
> 87:     }
> 88:   } while (Atomic::cmpxchg(&_head, elementIndex, elementIndex + 1) != elementIndex);

Why do we need atomic operations if we hold the enqueue lock. ??

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2127755502