iai-callgrind

iai-callgrind uses Valgrind's instruction-count measurements to provide deterministic, single-shot benchmarks that detect sub-1% regressions regardless of system load. This makes it ideal for CI environments where wall-clock benchmarks from divan or criterion would be noisy.

How it works

Instead of measuring elapsed time (which varies with CPU frequency, load, and thermal throttling), iai-callgrind counts the exact number of instructions executed. This gives perfectly reproducible results — a 0.5% instruction count increase is a real regression, not noise.

Trade-offs

iai-callgrind requires Valgrind (Linux/macOS only) and runs significantly slower than wall-clock benchmarks since it instruments every instruction. Use it in CI for regression gates, not for interactive development. Pair with divan for the full benchmarking workflow.