IBM POWER8 processor core microarchitecture

TLDR

The POWER8™ is IBM’s latest RISC microprocessor, introduced as frequency scaling slowed and the industry shifted toward adding cores rather than boosting single‑thread performance. The paper investigates the core microarchitecture innovations that enabled POWER8’s performance gains. POWER8 uses 22‑nm SOI technology with 15 metal layers to enhance single‑thread performance and single‑core throughput compared to POWER7. POWER8 achieves about 1.5× single‑thread performance and 2× single‑core throughput over POWER7, and with 50% more cores, it leads the industry in enterprise workload performance.

Abstract

The POWER8™ processor is the latest RISC (Reduced Instruction Set Computer) microprocessor from IBM. It is fabricated using the company's 22-nm Silicon on Insulator (SOI) technology with 15 layers of metal, and it has been designed to significantly improve both single-thread performance and single-core throughput over its predecessor, the POWER7® processor. The rate of increase in processor frequency enabled by new silicon technology advancements has decreased dramatically in recent generations, as compared to the historic trend. This has caused many processor designs in the industry to show very little improvement in either single-thread or single-core performance, and, instead, larger numbers of cores are primarily pursued in each generation. Going against this industry trend, the POWER8 processor relies on a much improved core and nest microarchitecture to achieve approximately one-and-a-half times the single-thread performance and twice the single-core throughput of the POWER7 processor in several commercial applications. Combined with a 50% increase in the number of cores (from 8 in the POWER7 processor to 12 in the POWER8 processor), the result is a processor that leads the industry in performance for enterprise workloads. This paper describes the core microarchitecture innovations made in the POWER8 processor that resulted in these significant performance benefits.