Profiling Builds¶

Analyze build performance to identify bottlenecks.

Chrome Trace¶

Generate Trace¶

rninja --trace build_trace.json

View Trace¶

Open Chrome
Navigate to chrome://tracing
Load build_trace.json

What to Look For¶

Long bars: Slow build steps
Gaps: Scheduling inefficiency
Serialization: Sequential dependencies

Build Statistics¶

rninja -d stats

Shows:

Total build time
Commands executed
Cache statistics

Explain Mode¶

rninja -d explain

Shows why targets are rebuilding.

Cache Analysis¶

rninja -t cache-stats

Low hit rate? Check:

Undeclared dependencies
Non-deterministic builds
Environment differences

Example Analysis¶

# 1. Generate trace
rninja --trace trace.json

# 2. Check stats
rninja -d stats

# 3. Check cache
rninja -t cache-stats

# 4. Investigate rebuilds
rninja -d explain

Common Issues¶

Issue	Symptom	Solution
Sequential builds	Gaps in trace	Add parallelism
Low cache hits	Rebuilding cached	Check deps
Slow no-op	> 100ms startup	Use daemon