Add configurable EventPipe CPU sampling rate via DOTNET_EventPipeCpuSamplingRate

[pavelsavara]

Summary

This change introduces a new DOTNET_EventPipeCpuSamplingRate environment variable that allows overriding the default EventPipe CPU sample profiler interval.

The default 1ms is too quick for WASM/browser.

This split from #126324 for smaller code review.

Changes

New config: DOTNET_EventPipeCpuSamplingRate

• src/coreclr/inc/clrconfigvalues.h — Register the new INTERNAL_EventPipeCpuSamplingRate DWORD config (default 0).
• src/native/eventpipe/ep-rt.h — Declare ep_rt_config_value_get_sampling_rate() in the shared EventPipe runtime abstraction header.
• src/native/eventpipe/ep.c — In ep_init(), read the configured rate and convert from milliseconds to nanoseconds. Falls back to the per-platform default when the value is 0.

Per-runtime implementations of ep_rt_config_value_get_sampling_rate

• src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.h — CoreCLR: reads via CLRConfig::GetConfigValue.
• src/coreclr/nativeaot/Runtime/eventpipe/ep-rt-aot.h — NativeAOT: reads via RhConfig::Environment::TryGetIntegerValue.
• src/mono/mono/eventpipe/ep-rt-mono.h — Mono: reads via g_getenv("DOTNET_EventPipeCpuSamplingRate").

Blazor/Browser WASM build integration

• src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets
  • Gate _AddWasmDiagnosticPortsEnvironmentVariable target on EnableDiagnostics=true.
  • Parse WasmPerformanceInstrumentation to extract an optional ,interval=<ms> suffix.
  • Pass the filter portion as DOTNET_WasmPerformanceInstrumentation and the interval (if present) as DOTNET_EventPipeCpuSamplingRate.

Miscellaneous fixes

• src/native/eventpipe/ds-ipc-pal-websocket.h

  • Wrap websocket extern declarations in extern "C" to prevent C++ name mangling (needed for JS interop in browser WASM).
  • Fix ds_rt_websocket_recv signature: remove incorrect const from the receive buffer parameter.

• src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.h

  • Add PROFILING_SUPPORTED preprocessor guard around ep_rt_notify_profiler_provider_created body.
  • Update #endif comments for clarity.

• src/native/eventpipe/ep-session.c

  • Add EP_ASSERT(session->buffer_manager != NULL) invariant check in the streaming loop shutdown path.

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[Copilot]

Pull request overview

Adds a new runtime-configurable knob (DOTNET_EventPipeCpuSamplingRate) to override EventPipe CPU sample-profiler interval (intended to allow slower sampling on WASM/browser), and wires it through CoreCLR/NativeAOT/Mono plus browser WASM build plumbing.

Changes:

• Introduce EventPipeCpuSamplingRate config/env var and consume it in EventPipe init (ms → ns conversion, 0 = default).
• Implement ep_rt_config_value_get_sampling_rate() for CoreCLR, NativeAOT, and Mono runtime layers.
• Update browser WASM SDK targets to pass DOTNET_EventPipeCpuSamplingRate (and related instrumentation env vars) and adjust websocket interop declarations.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/native/eventpipe/ep.c	Reads configurable sampling interval and applies it during ep_init().
src/native/eventpipe/ep-session.c	Adds an assert in the no-threads streaming loop shutdown path.
src/native/eventpipe/ep-rt.h	Adds runtime abstraction API for sampling-rate config retrieval.
src/native/eventpipe/ds-ipc-pal-websocket.h	Adjusts websocket externs for C++/interop and fixes recv buffer constness.
src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets	Adds EnableDiagnostics gating and parses WasmPerformanceInstrumentation for optional interval.
src/mono/mono/eventpipe/ep-rt-mono.h	Mono implementation of sampling-rate config getter via env var.
src/coreclr/vm/eventing/eventpipe/ep-rt-coreclr.h	CoreCLR implementation of sampling-rate config getter; minor preprocessor cleanup.
src/coreclr/nativeaot/Runtime/eventpipe/ep-rt-aot.h	NativeAOT implementation of sampling-rate config getter.
src/coreclr/inc/clrconfigvalues.h	Registers new CoreCLR config knob INTERNAL_EventPipeCpuSamplingRate.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.