RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v27]

[Aleksey Shipilev]

On Mon, 2 Jun 2025 11:32:27 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:
> 
>  - Tiny fixes
>  - Minor changes

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 30:

> 28: #include "runtime/orderAccess.hpp"
> 29: #include "utilities/ticks.hpp"
> 30: #include "jfr/periodic/sampling/jfrCPUTimeThreadSampler.hpp"

Include order?

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 60:

> 58:   assert(raw_thread->is_Java_thread(), "invariant");
> 59:   JavaThread* jt;
> 60:   if ((jt = JavaThread::cast(raw_thread))->is_exiting()) {

I see no point to be extra-smart with inline assignments here:

Suggestion:

  JavaThread* jt = JavaThread::cast(raw_thread);
  if (jt->is_exiting()) {

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 115:

> 113:   JfrCPUTimeSampleRequest* new_data = JfrCHeapObj::new_array<JfrCPUTimeSampleRequest>(capacity);
> 114:   JfrCHeapObj::free(_data, _capacity * sizeof(JfrCPUTimeSampleRequest));
> 115:   _data = new_data;

A bit of peak memory consumption improvement: don't have two things live at once. Plus, give the native allocator a chance to reuse the same location.

Suggestion:

  JfrCHeapObj::free(_data, _capacity * sizeof(JfrCPUTimeSampleRequest));
  _data = JfrCHeapObj::new_array<JfrCPUTimeSampleRequest>(capacity);

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2120895107
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2120897472
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2120909443