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 590:

> 588:   // so samples might be skipped and we have to compute the actual period
> 589:   int64_t period = get_sampling_period() * (info->si_overrun + 1);
> 590:   request._cpu_time_period = Ticks(period / 1000000000.0 * JfrTime::frequency()) - Ticks(0);

Are you treating JfrTime::frequency() as nanos here? JfrTime::frequency() can be in ticks, hence not a valid conversion.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 630:

> 628: 
> 629: bool JfrCPUTimeThreadSampler::create_timer_for_thread(JavaThread* thread, timer_t& timerid) {
> 630:   if (thread->osthread() == nullptr || thread->osthread()->thread_id() == 0){

When is this possible?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2106229890
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2106230710