gputrace

gputrace parses and analyzes Apple Metal GPU trace files (.gputrace bundles).

Installation

go install github.com/tmc/gputrace/cmd/gputrace@latest

Verify installation:

gputrace version

Quick Start

# Show trace statistics (dispatch counts, kernel names, timing)
gputrace stats trace.gputrace

# Full profiler breakdown (timing, pipelines, execution cost)
gputrace profiler trace.gputrace

# Export to pprof format for use with go tool pprof
gputrace pprof trace.gputrace -o trace.pb
go tool pprof -http=:8080 trace.pb

# View text timeline or export Chrome/Perfetto timeline
gputrace timeline trace.gputrace --format perfetto -o trace.json

# Compare two traces
gputrace diff A.gputrace B.gputrace --explain

Commands

Group	Command	Description
Overview	stats	Comprehensive trace statistics
	api-calls	API call sequences
	dump	Raw API call dump
Kernel & Shader	shaders	Shader performance metrics
	kernels	Kernel functions and pipeline mappings
	shader-source	Source-level performance attribution
Timing & Profiling	timing	Timing metrics export
	profiler	GPU profiler data extraction
	pprof	pprof format export
	correlate	Correlate timing with hardware metrics
Command Buffers	command-buffers	Command buffer analysis
	encoders	Compute encoder listing
Buffer Analysis	buffers	Buffer listing and properties
	buffer-access	Buffer access patterns
	buffer-timeline	Buffer allocation timeline
Visualization	timeline	Text timeline and Chrome/Perfetto export
	graph	Graph visualization
	tree	Execution tree view
	diff	Compare two traces
	insights	Actionable performance insights
Capture	xcode-profile	Xcode GPU profiler automation
	xcode-bindings	Inspect private Xcode GTShaderProfiler bindings
	xcode-parity	Audit Xcode metric parity for a trace
Utilities	mtlb	Metal Library Binary inspection
	clear-buffers	Zero out buffers to reduce trace size
	version	Print build version

Run gputrace [command] --help for details on any command.

Trace Diff

Compare two profiled traces and explain performance deltas at dispatch, kernel, encoder, and timeline-window levels:

# Human-readable summary
gputrace diff A.gputrace B.gputrace --explain

# Function and encoder views
gputrace diff A.gputrace B.gputrace --by function,encoder --limit 25

# Dispatch outliers (with source indices)
gputrace diff A.gputrace B.gputrace --by dispatch --min-delta-us 30 --limit 50

# JSON or CSV output
gputrace diff A.gputrace B.gputrace --json > diff.json
gputrace diff A.gputrace B.gputrace --csv --by function > function_deltas.csv

# Auto-discover newest trace pair and run quick triage
gputrace diff --bench-dir /path/to/bench-traces --quick

# Write markdown report
gputrace diff A.gputrace B.gputrace --md-out /tmp/report.md

See docs/TRACE_DIFF_WORKFLOW.md for the full workflow and sample output.

Testing

go test ./...

The repository includes small canonical fixtures under testdata/traces:

• 01-single-encoder for basic parsing and diff smoke tests
• 02-two-encoders, 03-three-encoders, 04-four-encoders, and 06-six-encoders for multi-encoder parsing
• known-invocations-*, low-alu-*, high-alu-*, low-occupancy-*, and high-occupancy-* for focused counter and shader-metric scenarios

Some success paths require capabilities that are not shipped in the small in-repo fixtures:

• profiler requires profiled traces with .gpuprofiler_raw/streamData
• perf-counter validation and CSV import require local .gpuprofiler_raw counter records or Xcode Counters.csv exports
• shader-source requires traces with source attribution data

See docs/TESTING.md for opt-in integration test environment variables and fixture handling.

Documentation

Detailed format and workflow documentation lives in docs/:

• README.md -- docs index
• ENVIRONMENT.md -- environment variables
• TESTING.md -- test fixtures and opt-in integration tests
• TRACE_DIFF_WORKFLOW.md -- trace diff workflow and output interpretation
• STREAMDATA_FORMAT.md -- streamData plist format
• trace-format.md -- trace format overview

Reverse-engineering notes and implementation status documents live in docs/research/.

GPU Timing Methodology

.gputrace files do not contain pre-computed timing percentages. Xcode Instruments derives shader cost by replaying captured GPU workloads with performance counters enabled. This library uses .gpuprofiler_raw/streamData for measured timing when profiler data is present: APSTimelineData ReplayerGPUTime, command-buffer timestamps, and encoder/dispatch cumulative offsets. Execution-cost sampling from Profiling_f_*.raw and GPRWCNTR encoder profiles are reported as counter/profile annotations, not as wall-clock timing sources. Non-profiled traces may emit approximate extracted or synthetic timing for visualization and triage; treat those values as estimates.

Developer Convenience

For local macOS reinstall and permission setup:

make reinstall

License

MIT License. See LICENSE for details.