An Accurate and Energy-Efficient Way Determination Technique for Instruction Caches by Early Tab Matching

Abstract

This paper proposes an accurate and energy-efficient way determination (instead of prediction) technique for reducing energy consumption in the instruction cache by using early tag matching. Way prediction has been considered as one of the most efficient techniques to reduce energy consumption in the caches. The proposed scheme allows early tag matching for accurate way determination. With this feature, our scheme drastically improves the way determination accuracy compared to the previous way prediction techniques. To enable the early tag matching, the tag lookup stage is inserted prior to the fetch stage in the pipeline architecture. The tag matching is performed during the tag lookup stage, and then only one way is accessed during the fetch stage, leading to good energy efficiency. Simulation results show that the proposed technique reduces the energy consumption in the instruction cache by 55.1% on average. Moreover, our technique guarantees negligible performance degradation by overlapping two pipeline stages in case of branch misprediction.

A Buffered Dual-Access-Mode Scheme Designed for Low-Power Highly-Associative Caches

“…The performance and power efficiency of way-prediction cache is highly dependent on the accuracy of a wayprediction algorithm used. Chung et al (2008) proposes a pipeline change for way determination. An early tag lookup stage, between branch prediction and fetch stage, is used to determine the next way to be accessed.…”

“…In this method, prediction accuracy and hit rate of the original way-prediction cache are maintained while reducing power consumption. Chung et al (2008) did not evaluate this scheme for data caches since the early tag lookup stage was proposed for instruction cache only.…”