RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v16]

[Robert Toyonaga]

On Mon, 26 May 2025 19:38:16 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:
> 
>   Remove mistake

src/hotspot/share/jfr/recorder/service/jfrEventThrottler.cpp line 89:

> 87:   }
> 88:   if (event_id == JfrCPUTimeSampleEvent) {
> 89:     return _disabled_cpu_time_sample_throttler;

Why do you need to make a "disabled" throttler? Shouldn't the rate limiting always be done by the arguments given to `timer_create`? The actual JFR throttling mechanism used by `ObjectAllocationSample` doesn't really fit this use-case anyway since you can already pre-determine the rate at which events are emitted (while with `ObjectAllocationSample` you can't).

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2107808894