dotnet-pgo: support supplementary perf sample files for SPGO and call graph

[benaadams]

Summary

dotnet-pgo create-mibc builds its call graph (for Pettis-Hansen method layout) and SPGO block counts from SampledProfileTraceData events in ETW/EventPipe traces. However, when using Linux perfcollect traces, the perf CPU samples in perf.data are not converted to SampledProfileTraceData events in the .etlx - they remain as raw IP addresses in perf.data.txt.

This means:

1. Pettis-Hansen gets no call graph data - CallWeights is empty, method layout is silently skipped
2. SPGO block attribution misses perf samples - only ETW-originated samples are attributed

Proposal

Add two optional parameters to dotnet-pgo create-mibc:

--supplementary-samples <file>

A text file with one hex instruction pointer per line (leaf IP of each CPU sample). These are fed to SampleCorrelator.AttributeSamplesToIP() for SPGO basic block attribution.

--supplementary-callgraph <file>

A text file with callee_hex_ip caller_hex_ip pairs per line (adjacent frames from CPU sampling callstacks). These are resolved against the MethodMemoryMap to populate callGraph and exclusiveSamples for Pettis-Hansen method layout.

Both files can be trivially extracted from perfcollect's perf.data.txt by parsing the callstack frames.

Context

We're building a PGO pipeline for Nethermind (Ethereum execution client) using perfcollect for CPU sampling on Linux. The pipeline works end-to-end but requires patching dotnet-pgo at build time to read these supplementary files.

Currently we extract ~9.6M perf samples from perfcollect traces, of which ~1.9M are attributed to managed code (the rest is kernel/native). This produces SPGO block counts for 1,350 methods across 32 assemblies. The call graph data would enable Pettis-Hansen method layout which is currently a no-op due to missing CallWeights.

Related issues:

• dotnet-pgo: SPGO fails with perfcollect LTTng traces — missing MethodDetails CTF mapping in TraceEvent #125883 - SPGO fails with perfcollect traces (CTF mapping issues)
• Fix dotnet-pgo SPGO crash in FlowSmoothing.MakeGraphFeasible #125896 - FlowSmoothing crash in SPGO
• Add MethodDetails CTF event mapping for LTTng trace support microsoft/perfview#2392 - Missing CTF event mappings in TraceEvent

Alternative

Ideally, CreateFromLinuxEventSources in TraceEvent would properly correlate perf.data samples with CLR method maps and produce SampledProfileTraceData events in the .etlx. This would make the supplementary files unnecessary. However, the current implementation doesn't do this correlation for perfcollect traces, and fixing it in TraceEvent is a larger change.

[benaadams]

Filed microsoft/perfview#2393 for the underlying TraceEvent issue - CreateFromLinuxEventSources should produce SampledProfileTraceData events from perf.data so this supplementary file workaround becomes unnecessary.