Compiler Support for Software Prefetching
This work was also published as a Rice University thesis/dissertation: http://hdl.handle.net/1911/19289
Due to the growing disparity between processor speed and main memory speed, techniques that improve cache utilization and hide memory latency are often needed to help applications achieve peak performance. Compiler-directed software prefetching is a hybrid software/hardware strategy that addresses this need. In this form of prefetching, the compiler inserts cache prefetch instructions into a program during the compilation process. During the program's execution, the hardware executes the prefetch instructions in parallel with other operations, bringing data items into the cache prior to the point where they are actually used, eliminating processor stalls due to cache misses. In this dissertation, we focus on the compiler's role in software prefetching. In a set of experimental studies, we evaluate the performance of current software prefetching strategies, first for sequential benchmark programs running on a simulated uniprocessor machine, and then for a set of parallel benchmarks on a simulated distributed shared memory (DSM)multiprocessor. In these experiments, we employ a variety of enhanced efficiency metrics that allow us to focus on the compiler-related aspects of software prefetching. Based on the results of our experiments, we propose and experimentally evaluate a series of new compiler techniques for software prefetching. Our contributions include more powerful forms of compile-time reuse analysis, to reduce the frequency of useless prefetches, and new strategies for scheduling prefetches that reduce penalties incurred due to late prefetches. In the area of prefetching for DSM multiprocessors, we present a novel data-flow framework for analyzing communication patterns within parallel programs. We show how a compiler can use the information generated by this framework to provide better prefetching for long-latency coherence misses.