[release/10.0] Backport CoreCLR portion of #127292: configurable EventPipe CPU sampling rate

[steveisok]

Note

This pull request was prepared with assistance from GitHub Copilot.

Backport of the CoreCLR / NativeAOT portion of #127292 to release/10.0.

Adds DOTNET_EventPipeThreadSamplingRate config so the EventPipe CPU sample profiler interval can be overridden from the default. Useful for diagnostic scenarios where the default 1ms interval is too aggressive.

Files included (6)

• src/coreclr/inc/clrconfigvalues.h — register INTERNAL_EventPipeThreadSamplingRate
• src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.h — CoreCLR implementation reading via CLRConfig::GetConfigValue. Also picks up the small PROFILING_SUPPORTED guard fix on ep_rt_notify_profiler_provider_created that was bundled in the original PR.
• src/coreclr/nativeaot/Runtime/eventpipe/ep-rt-aot.h — NativeAOT implementation reading via RhConfig::Environment::TryGetIntegerValue.
• src/native/eventpipe/ep-rt.h — shared declaration of ep_rt_config_value_get_sampling_rate.
• src/native/eventpipe/ep.c — ep_init reads the configured rate (ms) and converts to ns, falling back to the per-platform default when 0.
• src/mono/mono/eventpipe/ep-rt-mono.h — minimal Mono implementation so the shared ep.c continues to compile for Mono. Without this stub the Mono build would break.

Excluded from this backport

The Browser/WASM-specific pieces from #127292 are intentionally omitted:

• src/mono/browser/build/WasmApp.InTree.props
• src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
• src/mono/mono/eventpipe/ep-rt-mono-runtime-provider.c cleanup
• src/native/eventpipe/ds-ipc-pal-websocket.h browser-only extern "C" / signature fix
• src/native/eventpipe/ep-session.c assert tidy-up

Validation

Built locally on osx-arm64:

• ./build.sh -s clr.runtime+clr.nativeaotruntime -c Release → succeeded, 0 warnings, 0 errors
• ./build.sh -s mono.runtime -c Release → succeeded, 0 warnings, 0 errors

Original PR

#127292 — Add configurable EventPipe CPU sampling rate via DOTNET_EventPipeThreadSamplingRate by @pavelsavara, merged to main as 4e8ab2d.

[steveisok]

I need to change the PR description to the typical backport template

[Copilot]

Pull request overview

This PR backports the CoreCLR/NativeAOT portion of #127292 onto release/10.0, adding a DOTNET_EventPipeThreadSamplingRate configuration knob so the EventPipe CPU sample profiler interval can be overridden from the default (1ms).

Changes:

• Adds a new CoreCLR config value (INTERNAL_EventPipeThreadSamplingRate) and runtime-specific implementations to read the sampling interval (ms).
• Updates EventPipe initialization to apply the configured sampling rate (ms → ns), falling back to platform defaults when unset/0.
• Includes a small CoreCLR PROFILING_SUPPORTED guard adjustment for ep_rt_notify_profiler_provider_created, plus a Mono stub implementation to keep shared native EventPipe code building.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/coreclr/inc/clrconfigvalues.h	Registers INTERNAL_EventPipeThreadSamplingRate CoreCLR knob (ms, 0 = default).
src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.h	Implements CoreCLR getter via CLRConfig and adjusts profiler-provider notification guard.
src/coreclr/nativeaot/Runtime/eventpipe/ep-rt-aot.h	Implements NativeAOT getter via RhConfig::Environment::TryGetIntegerValue (decimal).
src/native/eventpipe/ep-rt.h	Declares ep_rt_config_value_get_sampling_rate() in the shared runtime abstraction.
src/native/eventpipe/ep.c	Reads the configured sampling rate in ep_init and applies it (ms → ns).
src/mono/mono/eventpipe/ep-rt-mono.h	Adds a Mono implementation reading DOTNET_/COMPlus_EventPipeThreadSamplingRate for build compatibility.

[pavelsavara]

It would be good to test it on Net11 on non-wasm OS before we backport it.

[steveisok]

Note

This comment was authored with assistance from GitHub Copilot.

Added a regression test in 8277aea covering the new DOTNET_EventPipeThreadSamplingRate knob.

Test: src/tests/tracing/eventpipe/samplingrate/

Design — two-process, same binary:

• Parent spawns a child via Process.Start with DOTNET_EventPipeThreadSamplingRate=50 set in StartInfo.Environment (the runtime reads the value in ep_init during startup, so it has to be set before the .NET process launches).
• Child runs IpcTraceTest.RunAndValidateEventCounts against itself, subscribes to Microsoft-DotNETCore-SampleProfiler, burns CPU for ~3 s, then inspects ThreadSample events (provider name + event ID 0, to avoid relying on the friendly event name).
• Validation on the busiest sampled thread:
  • count >= 30 — sanity: sampling actually happened
  • count <= 600 — rejects the default ~1 ms rate (which produces ~1500 samples/thread in 3 s)
  • median inter-sample interval >= 20 ms — also rejects the default ~1 ms rate

Local verification on osx-arm64:

• With env var set: 36 samples/thread, median interval 85 ms → PASS
• Without env var (i.e. knob ignored): 1573 samples/thread → FAIL with the targeted error message

This is intended to be upstreamed to main as a follow-up if the backport lands.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.