feat(jmh-fork): add perf-map JVMTI agent for source-aware JIT symbol resolution by not-matthias · Pull Request #7 · CodSpeedHQ/codspeed-jvm

not-matthias · 2026-04-15T13:52:54Z

Key features:

Resolves project source files to absolute paths via git root discovery
Falls back to clean relative paths for JDK/dependency classes
Thread-safe source file cache with pthread_once for git root init

codspeed-hq · 2026-04-15T14:06:41Z

Merging this PR will degrade performance by 19.51%

⚡ 1 improved benchmark
❌ 3 regressed benchmarks
✅ 121 untouched benchmarks
⏩ 9 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	`BASE`	`HEAD`	Efficiency
⚡	`fibonacciBottomUp[20]`	1.4 µs	1.2 µs	+15.52%
❌	`dualPivotQuickSort[10000]`	5.2 ms	6.4 ms	-19.51%
❌	`shellSort[1000]`	163.4 µs	182.6 µs	-10.5%
❌	`timSort[100]`	8.7 µs	10.2 µs	-14.81%

_{Comparing cod-2516-investigate-node-origin-for-java (c7c19aa) with main (8cb09f5)}

9 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

Copilot

Pull request overview

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Copilot was unable to run its full agentic suite in this review.

Adds a Linux-only perf-map JVMTI agent that emits perf map entries with source-aware symbols (preferring absolute source paths resolved from the git root), plus Gradle wiring and integration tests to validate the generated perf map output.

Changes:

Added native JVMTI agent (libperf_map_agent.so) that listens to JIT code events and writes perf-map entries with path::class::method symbols.
Added Java attach helper (PerfMapAgent) and JUnit integration tests that launch a child JVM with the agent to validate output.
Updated jmh-core Gradle build to compile/package the agent and updated CI to run the Gradle-based tests.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
`jmh-fork/jmh-core/src/test/java/io/codspeed/perf_map_agent/PerfMapAgentTest.java`	Adds Linux-only integration tests that validate map file creation and basic line format/content.
`jmh-fork/jmh-core/src/main/java/io/codspeed/perf_map_agent/c/perf_map_agent.c`	Implements the JVMTI agent, source-path resolution via git root discovery + recursive search, and a thread-safe cache.
`jmh-fork/jmh-core/src/main/java/io/codspeed/perf_map_agent/PerfMapAgent.java`	Adds a small Java CLI/API for attaching the agent to a running JVM by PID.
`jmh-fork/jmh-core/build.gradle.kts`	Compiles the perf-map agent on Linux and includes it in resources.
`.github/workflows/ci.yml`	Switches CI test execution to Gradle and enables Gradle caching.

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…resolution Add a JVMTI agent that hooks CompiledMethodLoad events and writes /tmp/perf-<pid>.map with source file paths resolved from the git root. Key features: - Resolves project source files to absolute paths via git root discovery - Falls back to clean relative paths for JDK/dependency classes - Thread-safe source file cache with pthread_once for git root init - VMDeath callback flushes deferred CompiledMethodLoad events - Handles lambda/hidden class signatures ($$Lambda/0x...) correctly - Java attach wrapper (PerfMapAgent) for runtime agent loading Includes integration tests validating perf map format, source path resolution, and default map path behavior.

The Maven job couldn't run the perf-map agent integration tests because it doesn't build the native lib. Switch to Gradle which compiles the native agent and runs all CodSpeed tests in a single job.

…CodSpeed When running under CodSpeed (isInstrumented()), load the perf-map JVMTI agent into benchmark JVMs: - Forked JVMs (@fork 1+): inject -agentpath: into the fork command - Current VM (@fork 0): self-attach via the Attach API, relying on -Djdk.attach.allowAttachSelf=true set by the CodSpeed runner The native library is extracted from classpath resources once and cached. Silently skipped when not available (non-Linux, not built).

…symbol resolution

GuillaumeLagrange

olgtm

Replace the hand-rolled gcc Exec tasks with Gradle's cpp-library plugin via two new nested subprojects (jmh-core:native-instrument-hooks and jmh-core:native-perf-map-agent). Each subproject owns its .c sources and — for instrument-hooks — the upstream submodule; jmh-core consumes their linkRelease outputs as resources bundled into jmh-core.jar. Notes: - Gradle 9.0 removed the c-library plugin; cpp-library is used with -x c to keep .c files compiling as C under g++. - cpp-library's source set filters for *.cpp/*.cc/*.c++, so .c files are added directly to the CppCompile task to bypass that filter. - The native subprojects are excluded from the shared maven-publish block; only jmh-core ships, with both .so files at its jar root.

not-matthias force-pushed the cod-2516-investigate-node-origin-for-java branch from 0220c52 to 02a8fe5 Compare April 15, 2026 14:07

not-matthias requested a review from Copilot April 15, 2026 14:50

Copilot AI reviewed Apr 15, 2026

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not-matthias force-pushed the cod-2516-investigate-node-origin-for-java branch from 15d9130 to c61df2c Compare April 15, 2026 16:02

not-matthias mentioned this pull request Apr 15, 2026

chore: remove DumpPerfMapAtExit in favor of custom dumper CodSpeedHQ/codspeed#295

Open

not-matthias requested a review from GuillaumeLagrange April 15, 2026 18:02

not-matthias force-pushed the cod-2516-investigate-node-origin-for-java branch from de2844f to 802ab83 Compare April 16, 2026 10:53

not-matthias added 4 commits April 16, 2026 13:13

fix(ci): replace Maven test job with Gradle

1dc460a

The Maven job couldn't run the perf-map agent integration tests because it doesn't build the native lib. Switch to Gradle which compiles the native agent and runs all CodSpeed tests in a single job.

chore(jmh-fork): compile native libs with -O3

eecaad1

not-matthias force-pushed the cod-2516-investigate-node-origin-for-java branch from 802ab83 to eecaad1 Compare April 16, 2026 11:13

fixup! feat(jmh-fork): add perf-map JVMTI agent for source-aware JIT …

e1b33bc

…symbol resolution

GuillaumeLagrange approved these changes Apr 16, 2026

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Comment thread jmh-fork/jmh-core/build.gradle.kts Outdated

Comment thread .github/workflows/ci.yml

not-matthias force-pushed the cod-2516-investigate-node-origin-for-java branch from b84d250 to c7c19aa Compare April 16, 2026 18:01

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feat(jmh-fork): add perf-map JVMTI agent for source-aware JIT symbol resolution#7

feat(jmh-fork): add perf-map JVMTI agent for source-aware JIT symbol resolution#7
not-matthias wants to merge 6 commits intomainfrom
cod-2516-investigate-node-origin-for-java

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not-matthias commented Apr 15, 2026

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Merging this PR will degrade performance by 19.51%

Performance Changes

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codspeed-hq bot commented Apr 15, 2026 •

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