The Stanford Hydra CMP

The Hydra chip multiprocessor (CMP) integrates four MIPS-based processors and their primary caches on a single chip together with a shared secondary cache. A standard CMP offers implementation and performance advantages compared to wide-issue superscalar designs. However, it must be programmed with a more complicated parallel programming model to obtain maximum performance. To simplify parallel programming, the Hydra CMP supports thread-level speculation and memory renaming, a paradigm that allows performance similar to a uniprocessor of comparable die area on integer programs. This article motivates the design of a CMP, describes the architecture of the Hydra design with a focus on its speculative thread support, and describes our prototype implementation. Chip multiprocessors offer an economical, scalable architecture for future microprocessors. Thread-level speculation support allows them to speed up past software.