Cache write policies and performance

Abstract

This paper investigates issues involving writes and caches. First, tradeoffs on writes that miss in the cache are investigated. In particular, whether the missed cache block is fetched on a write miss, whether the missed cache block is allocated in the cache, and whether the cache line is written before hit or miss is known are considered. Depending on the combination of these polices chosen, the entire cache miss rate can vary by a factor of two on some applications. The combination of no-fetch-on-write and write-allocate can provide better performance than cache line allocation instructions. Second, tradeoffs between write-through and write-back caching when writes hit in a cache are considered. A mixture of these two alternatives, called write caching is proposed. Write caching places a small fully-associative cache behind a write-through cache. A write cache can eliminate almost as much write traffic as a write-back cache.