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/jfrCPUTimeThreadSampler.cpp line 520:

> 518:   // the sampling period might be too low for the current Linux configuration
> 519:   // so samples might be skipped and we have to compute the actual period
> 520:   int64_t period = get_sampling_period() * (info->si_overrun + 1);

Does this calculation have to be done on every signal, by every thread? It seems like something that could be precalculated when the period is set?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2124980054