Access region locality for high-bandwidth processor memory system design

This paper studies an interesting yet less explored behavior of memory access instructions, called access region locality. Unlike the traditional temporal and spatial data locality that focuses on individual memory locations and how accesses to the locations are inter-related, the access region locality concerns with each static memory instruction and its range of access locations at run time. We consider program's data, heap, and stack regions in this paper. Our experimental study using a set of SPEC95 benchmark programs shows that most memory reference instructions access a single region at run time. Also shown is that it is possible to accurately predict the access region of a memory instruction at run time by scrutinizing the addressing mode of the instruction and the past access region history of it. A simple run-time access region predictor is developed that is similar to a branch predictor in structure. We describe and evaluate a superscalar processor with two distinct sets of memory pipelines, driven by the access region predictor. Experimental results indicate that the proposed mechanism is very effective in providing high memory bandwidth to the processor, resulting in comparable or better performance than a conventional memory design with a heavily multi-ported data cache that can lead to much higher hardware complexity.