Software assistance for data caches

Abstract

Hardware and software cache optimizations are active fields of research, that have yielded powerful but occasionally complex designs and algorithms. The purpose of this paper is to investigate the performance of combined through simple software and hardware optimizations. Because current caches provide little flexibility for exploiting temporal and spatial locality, two hardware modifications are proposed to support these two kinds of locality. Spatial locality is exploited by using large virtual cache lines which do not exhibit the performance flaws of large physical cache lines. Temporal locality is exploited by minimizing cache pollution with a bypass mechanism that still allows to exploit spatial locality. Subsequently, it is shown that simple software informations on the spatial/temporal locality of array references, as provided by current data locality optimization algorithms, can be used to increase cache performance significantly. The performance and design tradeoffs of the proposed mechanisms are discussed, Software-assisted caches are also shown to provide a very convenient support for further enhancement of data locality optimizations.