noisy benchmarks

I regularly see 10% swings in performance. Typically if I run the benches 3 times, I'll see a spread of at least 10%.

Is anyone else seeing this? I haven't yet figured out why, but it renders the benchmarks nearly useless if you can't safely measure a 10% change in behavior.

P.S. I noticed this while trying to evaluate #37

The issue names no benchmark files, commands, or tests. Start by reproducing the reported three-run spread and compare the benchmark results while investigating why measurements vary; done means identifying the source of the noise and establishing reliable performance measurements.

Written by the indexing model from the issue text.