DCC: Double capacity Cache architecture for narrow-width values

Abstract

Modern caches are designed to hold 64-bits wide data, however a proportion of data in the caches continues to be narrow width. In this paper, we propose a new cache architecture which increases the effective cache capacity up to 2X for the systems with narrow-width values, while also improving its power efficiency, bandwidth, and reliability. The proposed double capacity cache (DCC) architecture uses a fast and efficient peripheral circuitry to store two narrow-width values in a single wordline. In order to minimize the latency overhead in workloads without narrow-width data, the flag bits are added to tag store. The proposed DCC architecture decreases cache miss-rate by 50%, which results in 27% performance improvement and 30% higher dynamic energy efficiency. To improve reliability, DCC modifies the data distribution on individual bits, which results in 20% and 25% average static-noise margin (SNM) improvement in L1 and L2 caches respectively.