R.I.P. Geomean Speedup Use Equal-Work (Or Equal-Time) Harmonic Mean Speedup Instead

How to accurately summarize average performance is challenging. While geometric mean speedup is prevalently used, it is meaningless. Instead, this paper argues for harmonic mean speedup which accurately summarizes how much faster a workload executes on a target system relative to a baseline. We propose the equal-work and equal-time harmonic mean speedup metrics to explicitly expose the different assumptions they make, and we further suggest that equal-work speedup is most relevant to computer architecture research. The paper demonstrates that which average speedup is used matters in practice as inappropriate averages may lead to incorrect conclusions.