[browser] samplepoint instrumentation into Mono profiler

[pavelsavara]

Motivation

Collect sample stack traces in the single-threaded browser.
Single threaded environment can't have dedicated thread for "stop-the-world + collect stack traces" implementation.
So we need to collect samples by instrumenting the code instead.

Previously we implemented browser based profiler which collects "sample" on every method entry/leave. In realistic application, that generates too much traffic for the browser profiler.

This enhancement could also be used to implement sampling profiler with ST diagnostic server.

Goal

• add new samplepoint instrumentation into Mono profiler, use the existing enter/leave too.
• inject the event/call into same locations as GC safepoint.
  • we can skip emitting it at the method start, because there is already method_enter event/instrumentation.
  • This is also same location where cooperative MT would stop-the-world to take a sample.
• take sample on each Nth visit to the samplepoint (because measuring current time is more expensive)
• keep updating the size of N to match expected sample time interval

Implementation

• new interp IR instruction MINT_PROF_SAMPLEPOINT
• new profiler event method_samplepoint
• new Mono JIT method mini_profiler_emit_samplepoint
• new config option sampleIntervalMs for browser profiler. 1ms by default. All samples when set to 0.
• example of code emitted by AOT with call $mono_profiler_raise_method_samplepoint
• new jiterp helper append_profiler_event calling new mono_jiterp_prof_enter, mono_jiterp_prof_samplepoint, mono_jiterp_prof_leave
• new interp macro INTERP_PROFILER_RAISE
• changes JavaScript called only to get time mono_wasm_profiler_now and mono_wasm_profiler_record
• all sampling logic in browser.c new should_record_frame
• stack of start times profiler_stack and skip counter sample_skip_counter
• default sample interval 10ms
• callspec parametr to profiler allows to filter the instrumentation, for example by namespace callspec=N:Sample.FooNs

Todo

• how to

Contributes to #76316

[pavelsavara]

Interpreter: 1ms, skip rate between 200-500 sample points.

[hakenr]

Hi @pavelsavara,
I'm in! I'll try to reach you via Teams.