Managing Short-Lived and Long-Lived Values in Coarse-Grained Reconfigurable Arrays
Efficient storage in spatial processors is increasingly important as such devices get larger and support more concurrent operations. Unlike sequential processors that rely heavily on centralized storage, e.g. register files and embedded memories, spatial processors require many small storage structures to efficiently manage values that are distributed throughout the processor's fabric. The goal of this work is to determine the advantages and disadvantages of different architectural structures for storing values on-chip when optimizing for energy efficiency as well as area. Examination of applications for coarse-grained reconfigurable arrays (CGRAs) shows that most values are short-lived; they are produced and consumed quickly, but the distribution of value lifetimes has a reasonably long tail. We take advantage of this distribution to optimize register storage structures for managing short-, medium-, and long-lived values. We show that using a combination of register storage structures, each tailored for values with different lifetimes, provides a reduction in overall area-energy product to 0.69× the area-energy of the baseline architecture, without loss of performance. Finally we provide energy profiles, characteristics, and comparisons of each register structure to enable architects to guide future design choices.