REMcode: relocating embedded code for improving system efficiency

Abstract

The memory hierarchy subsystem has a significant impact on performance and energy consumption of an embedded system. Methods which increase the hit ratio of the cache hierarchy will typically enhance the performance and reduce the embedded system's total energy consumption. This is mainly due to reduced cache-to-memory bus transactions, fewer main memory accesses and fewer processor waiting cycles. A heuristic approach is presented to reduce the total number of cache misses by carefully relocating selected sections of the application's software code within the main memory, thus reducing conflict misses resulting from the cache hierarchy. The method requires no hardware modifications i.e. it is a software-only approach. For the first time such a method is applied to large program traces, and the miss rates and corresponding energy savings are observed while varying cache size, line size and associativity. Relocating the code consistently produces superior performance on direct-mapped cache. Since direct-mapped caches, being smaller in silicon area than caches with higher associativity (for the same size), cost less in terms of energy/access, and access faster, using direct-mapped instruction cache with code relocation for performance-oriented embedded systems is recommended. A maximum cache miss rate reduction from 71% down to less than 1% is achieved, with energy reductions of up to 63% with only a small increase in main memory size.