Evaluation of Memory Prefetching Techniques for Modem Applications

Sammanfattning

Processor performance has increased far faster than memories have been able to keep up with, forcing processor designers to use caches in order to bridge the speed difference. This can increase performance significantly for programs that utilize the caches efficiently but results in significant performance penalties when data is not in cache. One way to mitigate this problem is to to make sure that data is cached before it is needed using memory prefetching. This thesis focuses on different ways to perform prefetching in systems with strict area and energy requirements by evaluating a number of prefetch techniques based on performance in two programs as well as metrics such as coverage and accuracy. Both data and instruction prefetching are investigated. The studied techniques include a number of versions of next line prefetching, prefetching based on stride identification and history as well as post-increment based prefetching. While the best increase in program performance is achieved using next 2 lines prefetching it comes at a significant energy cost as well as drastically increased memory traffic making it unsuitable for use in energy-constrained applications. RPT-based prefetching on the other hand gives a good balance between performance and cost managing to improve performance by 4% and 7% for two programs while keeping the impact on both area and energy minimal.