Compiler-Directed Variable Latency Aware SPM Management to CopeWith Timing Problems

This paper proposes and experimentally evaluates a compiler-driven approach that operates an on-chip scratch-pad memory (SPM) assuming different latencies for the different SPM lines. Our goal is to reduce execution cycles without creating any reliability problems due to variations in access latencies. The proposed scheme achieves its goal by evaluating the reuse of different data items and adopting a reuse and latency aware data-to-SPM placement. It also employs data migration within SPM when it helps to cut down the number of execution cycles further. We also discuss an alternate scheme that can reduce latency of select SPM locations by controlling a circuit level mechanism in software to further improve performance. We implemented our approach within an optimizing compiler and tested its effectiveness through extensive simulations. Our experiments with twelve embedded application codes show that the proposed approach performs much better than the worst-case based design paradigm (16.2% improvement on the average) and comes close (within 5.7%) to an hypothetical best-case design (i.e., one with no process variation) where every SMP locations uniformly have low latency