An empirical survey of performance and energy efficiency variation on Intel processors

Traditional HPC performance and energy characterization approaches assume homogeneity and predictability in the performance of the target processor platform. Consequently, processor performance variation has been considered to be a secondary issue in the broader problem of performance characterization. In this work, we present an empirical survey of the variation in processor performance and energy efficiency on several generations of HPC-grade Intel processors. Our study shows that, compared to the previous generation of Intel processors, the problem of performance variation has become worse on more recent generation of Intel processors. Specifically, the performance variation across processors on a large-scale production HPC cluster at LLNL has increased to 20% and the run-to-run variation in the performance of individual processors has increased to 15%. We show that this variation is further magnified under a hardware-enforced power constraint, potentially due to the increase in number of cores, inconsistencies in the chip manufacturing process and their combined impact on processor's energy management functionality. Our experimentation with a hardware-enforced processor power constraint shows that the variation in processor performance and energy efficiency has increased by up to 4x on the latest Intel processors.