RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v27]
Aleksey Shipilev
shade at openjdk.org
Mon Jun 2 18:47:30 UTC 2025
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
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