Dynamic Scratch-Pad Memory Management for Irregular Array Access Patterns

There exist many embedded applications such as those executing on set-top boxes, wireless base stations, HDTV, and mobile handsets that are structured as nested loops and benefit significantly from a software managed memory. Prior work on scratchpad memories (SPMs) focused primarily on applications with regular data access patterns. Unfortunately, some embedded applications do not fit in this category and consequently conventional SPM management schemes will fail to produce the best results for them. In this work, we propose a novel compilation strategy for data SPMs for embedded applications that exhibit irregular data access patterns. Our scheme divides the task of optimization between compiler and runtime. The compiler processes each loop nest and insert code to collect information at runtime. Then, the code is modified in such a fashion that, depending on the collected information, it dynamically chooses to use or not to use the data SPM for a given set of accesses to irregular arrays. Our results indicate that this approach is very successful with the applications that have irregular patterns and improves their execution cycles by about 54% over a state-of-the-art SPM management technique and 23% over the conventional cache memories. Also, the additional code size overhead incurred by our approach is less than 5% for all the applications tested.