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/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 365:

> 363:   // idea: this ensures that the frames happened in native
> 364:   // maybe we can wrap this in #ifdef ASSERT if first_index is always 0
> 365:   s4 first_index = queue.size() - 1;

I'm afraid I don't understand this logic at all. If the intent is to share a sid over many requests, why are the individual requests passed to stacktrace.record_inner()?

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 373:

> 371:     }
> 372:   }
> 373:   assert(first_index == 0, "invariant");

How is this possible?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2106244737
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2106244850