A Rigorous Benchmarking and Performance Analysis Methodology for Python Workloads

Abstract

Computer architecture and computer systems research and development is heavily driven by benchmarking and performance analysis. It is thus of paramount importance that rigorous methodologies are used to draw correct conclusions and steer research and development in the right direction. While rigorous methodologies are widely used for native and managed programming language workloads, scripting language workloads are subject to ad-hoc methodologies which lead to incorrect and misleading conclusions. In particular, we find incorrect public statements regarding different virtual machines for Python, the most popular scripting language. The incorrect conclusion is a result of using the geometric mean speedup and not making a distinction between start-up and steady-state performance. In this paper, we propose a statistically rigorous benchmarking and performance analysis methodology for Python workloads, which makes a distinction between start-up and steady-state performance and which summarizes average performance across a set of benchmarks using the harmonic mean speedup. We find that a rigorous methodology makes a difference in practice. In particular, we find that the PyPy JIT compiler outperforms the CPython interpreter by 1.76 × for steady-state while being 2% slower for start-up, which refutes the statement on the PyPy website that ‘PyPy outperforms CPython by 4.4× on average’ based on the geometric mean speedup and not making a distinction between start-up and steady-state. We use the proposed methodology to analyze Python workloads which yields several interesting findings regarding PyPy versus CPython performance, start-up versus steady-state performance, the impact of a workload's input size, and Python workload execution characteristics at the microarchitecture level.