Analysis of memory latency factors and their impact on KSR1 performance

The KSRI has a shared address space, which spreads over physically distributed memory modules with various latencies. Thus performance depends considerably on the program's locality of reference and the effectiveness of using prefetch and post-store instructions. This paper analyzes the various memory latency factors which stall the processor during program execution, running on 32-processor system. A suitable model for evaluating these factors is developed for the execution of tiled do-loops with the slice strategy. The benchmark used is a sparse matrix solver. The limited size of the prefetch queue is shown to stall the processor for a long period of time, which reduces the benefit of prefetch considerably. The post-store operation is shown to have a high overhead. However, delaying the post-store operation improved performance considerably.<
>