RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v26]
Markus Grönlund
mgronlun at openjdk.org
Sun Jun 1 13:04:00 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 42:
> 40: #include "runtime/javaThread.hpp"
> 41: #include "runtime/osThread.hpp"
> 42: #include "runtime/safepointMechanism.hpp"
Not needed, since you have the .inline.hpp
src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 102:
> 100:
> 101: u4 JfrCPUTimeTraceQueue::size() const {
> 102: return Atomic::load(&_head);
Is this read from multiple threads? In that case, load_acquire().
src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 200:
> 198: void sample_thread(JfrSampleRequest& request, void* ucontext, JavaThread* jt, JfrThreadLocal* tl);
> 199:
> 200: // sample all threads that are in native state (and requested to be sampled)
We are not really "sampling", but processing their queues, no?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119128911
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119129239
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119129708
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