Exploring the Impacts of Software Cache Configuration for In-line Compressed Arrays

In order to compute on or analyze large data sets, applications need access to large amounts of memory. To increase the amount of physical memory requires costly hardware upgrades. Compressing large arrays stored in an application's memory does not require hardware upgrades, while enabling the appearance of more physical memory. In-line compressed arrays compress and decompress data needed by the application as it moves in and out of it's working set that resides in main memory. Naive compressed arrays require a compression or decompression operation for each store or load, respectively, which significantly hurts performance. Caching decompressed values in a software managed cache limits the number of compression/decompression operations, improving performance. The structure of the software cache impacts the performance of the application. In this paper, we build and utilize a compression cache simulator to analyze and simulate various cache configurations for an application. Our simulator is able to leverage and model the multidimensional nature of high-performance computing (HPC) data and compressors. We evaluate both direct-mapped and set-associative caches on five HPC kernels. Finally, we construct a performance model to explore runtime impacts of cache configurations. Results show that cache policy tuning by increasing the block size, associativity and cache size improves the hit rate significantly for all applications. Incorporating dimensionality further improves locality and hit rate, achieving speedup in the performance of an application by up to 28.25 %.