RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v29]

[Aleksey Shipilev]

On Mon, 2 Jun 2025 13:50:49 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 bug related to async stack walking

Scanned this briefly, would do another pass tomorrow.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 117:

> 115: 
> 116: bool JfrCPUTimeTraceQueue::is_empty() const {
> 117:   return Atomic::load(&_head) == 0;

Not entirely clear what is the memory semantics for accessing `_head`. Does it need to be acq/rel? If so, this one should be `::load_acquire`?

src/hotspot/share/memory/resourceArea.hpp line 46:

> 44: // A ResourceArea is an Arena that supports safe usage of ResourceMark.
> 45: class ResourceArea: public Arena {
> 46: 

All the changes in this file are unnecessary, please revert.

src/jdk.jfr/share/classes/jdk/jfr/internal/JVM.java line 281:

> 279:      * @param autoadapt true if the rate should be adapted automatically
> 280:      */
> 281:     public static native void setCPUThrottle(double rate, boolean autoadapt);

Suggestion:

    public static native void setCPUThrottle(double rate, boolean autoAdapt);

test/jdk/jdk/jfr/event/profiling/TestSamplingLongPeriod.java line 42:

> 40: public class TestSamplingLongPeriod {
> 41: 
> 42:     static String sampleEvent = EventNames.ExecutionSample;

Does not look necessary to change?

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PR Review: https://git.openjdk.org/jdk/pull/25302#pullrequestreview-2888004951
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121900364
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121610476
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121587105
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2121584954