Toward a unified model of program behavior

Abstract

In building a unified model of program behavior, the authors characterize spatial, temporal, and structural locality and their relationships to one another. Analysis and modeling of 40 VAX 8200, TI Explorer, and RISC processor traces indicate spatial prefetching actually increases the effectiveness of LRU replacement in exploiting temporal locality rather than decreasing it as might be expected. The lesser known structural locality is also shown to exist in a wide variety of workloads, and its relationship to spatial and temporal locality is also characterized. For the instruction reference stream, structural locality is shown to predict the next instruction to be fetched with higher accuracy than existing dynamic branch prediction techniques. A unified model incorporating all three types of locality is developed and validated by comparing the entropy of synthetically generated traces with that of the actual traces. While the model is accurate in predicting the next type of reference to be made, higherorder dependencies requiring further look-ahead remain to be modeled.