Demystifying multicore throughput metrics

Several different metrics have been proposed for quantifying the throughput of multicore processors. There is no clear consensus about which metric should be used. Some studies even use several throughput metrics. We show that there exists a relation between single-thread average performance metrics and throughput metrics, and that throughput metrics inherit the meaning or lack of meaning of the corresponding single-thread metric. We show that two popular throughput metrics, the weighted speedup and the harmonic mean of speedups, are inconsistent: they do not give equal importance to all benchmarks. Moreover we demonstrate that the weighted speedup favors unfairness. We show that the harmonic mean of IPCs, a seldom used throughput metric, is actually consistent and has a physical meaning. We explain under which conditions the arithmetic mean or the harmonic mean of IPCs can be used as a strong indicator of throughput increase.