Support jdk.CPUTimeSample event in ProfileResults for Java 25+ (JEP 509) by iprithv · Pull Request #15983 · apache/lucene

iprithv · 2026-04-24T21:58:49Z

Description

Java 25 added CPU-time profiling (JEP 509) which emits jdk.CPUTimeSample
events. ProfileResults did not recognize this event type, causing empty
profiling reports when the CPU-time profiler is active.

Resolves #15926

…+ (JEP 509)

mikemccand

Whoa, thank you for picking this up @iprithv -- I left some comments about maybe being less lenient about two sampling methods used a the same time.

mikemccand · 2026-04-27T11:47:34Z

+          // needed. When available, we skip legacy execution samples to avoid double-counting.
+          return name.equals("jdk.CPUTimeSample");
+        }
        return (name.equals("jdk.ExecutionSample") || name.equals("jdk.NativeMethodSample"))


I think NativeMethodSample is also a dup, if CPUTime and wall-clock sampling are both enabled?

Yes, I expanded the comment to say that explicitly so it matches the code. Thanks!

mikemccand · 2026-04-27T11:49:02Z

    <setting name="period">1 ms</setting>
  </event>

+  <event name="jdk.CPUTimeSample">


Could we turn off the old (wall-clock) sampling (jdk.ExecutionSample, jdk.NativeMethodSample) and just fully commit to CPUTime. In nightly benchmarks we've found the 1 msec sampling to add non-trivial overhead (I think ~5-7% slower).

The 1msec sampling was necessary for tests in order to find places wasting CPU. most tests just don't run that long.

Done,

Added gradle/testing/profiling.linux.jfc: legacy samplers off, jdk.CPUTimeSample on with a 1 ms throttle so short chunks still get dense enough samples.

Left gradle/testing/profiling.jfc for non-Linux with 1 ms ExecutionSample / NativeMethodSample.

CodeProfilingPlugin loads the Linux file when os.name contains linux, otherwise profiling.jfc.

Thanks both!

mikemccand · 2026-04-27T11:50:26Z

+
+    // Pre-scan to detect if CPU-time samples (Java 25+, JEP 509) are available.
+    // If so, prefer them over legacy execution samples to avoid double-counting.
+    boolean hasCPUTimeSamples = "cpu".equals(mode) && detectCPUTimeSamples(files);


Could we make this stricter? Throw an exception if we see a mix of CPUTime and legacy events? Lucene (and in general anyone profiling, hmm except maybe profiler debuggers heh) should only have one sampler enabled at a time?

I initially added the strict mixed-sampler check here, but removed it after @rmuir follow up review since the two Lucene JFC files are now mutually exclusive.

So the exclusivity now lives in the selected JFC config instead of a pre-scan in ProfileResults. Thanks!

rmuir · 2026-04-27T20:18:03Z

+   * Pre-scan recording files to detect if any jdk.CPUTimeSample events are present. When they are,
+   * we prefer them over legacy jdk.ExecutionSample/jdk.NativeMethodSample to avoid double-counting.
+   */
+  static boolean detectCPUTimeSamples(List<String> files) throws IOException {


Instead of this logic, should we just have profiling.linux.jfc that is loaded for linux, and profiling.jfc used for others?

Yes, done. Linux uses gradle/testing/profiling.linux.jfc, everyone else gradle/testing/profiling.jfc, selected in CodeProfilingPlugin from the host OS. Thanks!

Signed-off-by: prithvi <prithvisivasankar@gmail.com>

rmuir · 2026-04-27T21:41:33Z

    String name = event.getEventType().getName();
    switch (mode) {
      case "cpu":
+        if (hasCPUTimeSamples) {


I don't think we need this boolean parameter nor the if block.

Just something like:

return name.equals("jdk.CPUTimeSample") || name.equals("jdk.ExecutionSample") || name.equals("jdk.NativeMethodSample");

sure, updated. thanks!

rmuir · 2026-04-27T21:42:51Z

 <!--
-Collects only execution and method samples at a low interval
+  Wall-clock execution samples for CPU profiling on platforms where JEP 509 CPU-time sampling
+  is unavailable (non-Linux). On Linux, CodeProfilingPlugin uses profiling.linux.jfc instead.


I don't see a profiling.linux.jfc in your PR

my bad, missed it in adding in previous commit. Thanks!

rmuir · 2026-04-27T21:43:44Z

+   * wall-clock samples ({@code jdk.ExecutionSample} / {@code jdk.NativeMethodSample}); only one
+   * CPU sampler should be enabled in JFR settings.
+   */
+  static boolean resolveCpuTimeSampling(List<String> files) throws IOException {


Remove the whole function as the two files are mutually exclusive. This is very verbose and not needed.

sure, done. thanks!

rmuir · 2026-04-27T21:43:54Z

    }
+
+    // Pre-scan recordings: decide CPU-time vs legacy sampling and reject mixed configurations.
+    boolean hasCPUTimeSamples = "cpu".equals(mode) && resolveCpuTimeSampling(files);


nuke this one too

sure, removed this too. thanks!

Signed-off-by: prithvi <prithvisivasankar@gmail.com>

mikemccand

Thank you for the all the iterations @iprithv -- I think this is close!

mikemccand · 2026-04-28T13:31:50Z

+  /**
+   * JEP 509 CPU-time sampling ({@code jdk.CPUTimeSample}) is implemented on Linux. Use a Linux-only
+   * JFR template with CPU-time sampling only; other hosts keep wall-clock execution sampling for
+   * short tests.


Wait, it's for all tests, not just short tests right? Maybe just remove for short tests?

Sure, done. Updated. Thanks!

mikemccand · 2026-04-28T13:32:54Z

      Provider<Boolean> frametypesOption) {}
+
+  /**
+   * JEP 509 CPU-time sampling ({@code jdk.CPUTimeSample}) is implemented on Linux. Use a Linux-only


Maybe is currently (Java 25) implemented only on Linux, so we use a Linux-only JFR template...?

yes, updated. Thanks!

mikemccand · 2026-04-28T13:33:38Z

+   */
+  private static String profilingSettingsPath() {
+    String os = System.getProperty("os.name", "").toLowerCase(Locale.ROOT);
+    return os.contains("linux") ? "testing/profiling.linux.jfc" : "testing/profiling.jfc";


Actually, instead of baking linux in the name, could we use cputime? Maybe in the future other OS's can support CPU time sampling too...

Sure, makes sense. Thanks!

mikemccand · 2026-04-28T13:35:30Z

+-->
+<configuration version="2.0" label="TestProfilingLinux" description="CPU-time sampling for unit tests (Linux)" provider="Apache">
+  <event name="jdk.ExecutionSample">
+    <setting name="enabled">false</setting>


Oh, are these events enabled by default, so we have to have these entries (jdk.ExecutionSample and jdk.NativeMethodSample) to explicitly then disable them?

i think you are correct, I don't believe it is strictly necessary to have them in this file with enabled: false.

removed the explicit disabled entries. The CPU time template now only enables jdk.CPUTimeSample plus the allocation events used by heap profiling. Thanks!

mikemccand · 2026-04-28T13:37:59Z


 Build
 ---------------------
+* GITHUB#15926: Support jdk.CPUTimeSample event (Java 25+, JEP 509) in ProfileResults.


Can we word a bit more user-friendly-y? Maybe Use the new (Java 25+, JEP 509) CPU time sampling profiler when available (currently just on Linux), and fall back to the legacy wall-clock...?

sure, done. thanks!

Signed-off-by: prithvi <prithvisivasankar@gmail.com>

iprithv added 2 commits April 25, 2026 03:17

GITHUB#15926: Support jdk.CPUTimeSample in ProfileResults for Java 25…

78af0c1

…+ (JEP 509)

Merge branch 'main' into fix/profile-results-cputime-sample

f952eb7

github-actions Bot added the module:build-infra label Apr 24, 2026

github-actions Bot added this to the 11.0.0 milestone Apr 24, 2026

Updated CHANGES.txt

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mikemccand reviewed Apr 27, 2026

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rmuir reviewed Apr 27, 2026

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iprithv added 2 commits April 28, 2026 02:44

review changes

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Signed-off-by: prithvi <prithvisivasankar@gmail.com>

Merge branch 'main' into fix/profile-results-cputime-sample

ed3c9bf

iprithv requested review from mikemccand and rmuir April 27, 2026 21:30

rmuir reviewed Apr 27, 2026

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Signed-off-by: prithvi <prithvisivasankar@gmail.com>

iprithv requested a review from rmuir April 28, 2026 06:49

rmuir approved these changes Apr 28, 2026

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mikemccand reviewed Apr 28, 2026

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iprithv added 3 commits April 28, 2026 20:03

review changes

30d4510

Signed-off-by: prithvi <prithvisivasankar@gmail.com>

Merge branch 'main' into fix/profile-results-cputime-sample

0d78f10

review changes

6f2c12f

Signed-off-by: prithvi <prithvisivasankar@gmail.com>

iprithv requested a review from mikemccand April 28, 2026 14:49

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iprithv commented Apr 24, 2026

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