Bicep Perf Profiling Agent Skill

Bicep Performance Profiling

Capture a Release trace of bicep build --pattern, then use the filtrace MCP server to identify actionable compiler hotspots.

Prerequisites

• Run commands from the Bicep repository root.
• Ensure pwsh, the SDK pinned by global.json, and dotnet-trace are available.
• If needed, install dotnet-trace with dotnet tool install --global dotnet-trace.

Capture

Run the bundled profile script:

pwsh ./.github/skills/bicep-trace-analysis/scripts/BuildAndProfile.ps1 src/Bicep.Core.Samples/Files/user_submitted

The script:

• Builds Bicep.Cli in Release mode under src/Bicep.Cli/bin/profile/Release.
• Runs bicep build --pattern <folder>/**/*.bicep.
• Writes profile-<UTC timestamp>.nettrace to the current directory.
• Captures sampled thread stacks, common runtime events, verbose GC events, and sampled allocations.

Analyze

Use filtrace in this order:

• Run trace_info with the trace path and symbols=src/Bicep.Cli/bin/profile/Release.
• Require strong method-name resolution before interpreting rankings. Source mapping may be lower because framework PDBs are unavailable; ensure there are no PDB identity mismatches for Bicep assemblies.
• Run CPU trace_rank with both self and inclusive measures.
• Scope compiler rankings with root=Bicep.Cli.Commands.BuildCommand.Compile. Whole-process rankings include runtime service threads and sampled waits that can obscure compiler work.
• Run allocation trace_rank with both measures and run trace_gc for collection count, pause time, peak heap, and promoted bytes.
• Use trace_callers on hot framework leaves such as file I/O, JSON serialization, array growth, boxing, or locks until reaching the Bicep-owned caller.
• Use trace_tree for major Bicep phases and trace_lines or trace_heatmap only when matching PDBs provide sufficient source attribution.

Useful first-pass analyses:

trace_info(path, symbols)
trace_rank(path, metric=cpu, measure=self, root=Bicep.Cli.Commands.BuildCommand.Compile, symbols=symbols)
trace_rank(path, metric=cpu, measure=inclusive, root=Bicep.Cli.Commands.BuildCommand.Compile, symbols=symbols)
trace_rank(path, metric=alloc, measure=self)
trace_rank(path, metric=alloc, measure=inclusive)
trace_gc(path)

Report

Report the top five optimization areas. For each area include:

• The inclusive or self weight and percentage of the scoped compile workload.
• The Bicep-owned method or phase responsible for the cost.
• A concrete optimization hypothesis and the smallest experiment that could falsify it.
• Any overlap with another finding; inclusive percentages are not additive.

Call out capture limitations. Prefer a longer trace when a result has fewer than 200 samples, and do not claim allocation absence unless allocation capture is known to be enabled. Re-capture and compare like-for-like traces after any optimization.