RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v26]
Markus Grönlund
mgronlun at openjdk.org
Sun Jun 1 15:27:06 UTC 2025
On Sun, 1 Jun 2025 07:26:19 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 two additional commits since the last revision:
>
> - Refactoring
> - Remove convoluted native trace logic
src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 332:
> 330: JavaThread* jt = tlh.list()->thread_at(i);
> 331: JfrThreadLocal* tl = jt->jfr_thread_local();
> 332: if (tl != nullptr && tl->wants_async_processing_of_cpu_time_jfr_requests()) {
tl is never nullptr.
src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 344:
> 342:
> 343: // equals operator for JfrSampleRequest
> 344: inline bool operator==(const JfrSampleRequest& lhs, const JfrSampleRequest& rhs) {
Can be removed.
src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 574:
> 572:
> 573: if (queue.enqueue(request)) {
> 574: tl->set_has_cpu_time_jfr_requests(true);
This should only need to be set when enqueuing the first entry.
src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 581:
> 579:
> 580: if (jt->thread_state() == _thread_in_native &&
> 581: queue.size() > queue.capacity() * 2 / 3) {
Is this logic still valid? You are only asking for a async processing depending on the load factor of the queue?
src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 586:
> 584: JfrCPUTimeThreadSampling::trigger_async_processing_of_cpu_time_jfr_requests();
> 585: } else {
> 586: tl->set_do_async_processing_of_cpu_time_jfr_requests(false);
Was it true before and needed a reset?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119250661
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119250887
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119248176
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119248824
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119249381
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