Considerations in the Design of Hydra: a Multiprocessor-on-a-chip Microarchitecture

As more transistors are integrated onto larger dies, single-chip multiprocessors integrated with large amounts of cache memory will soon become a feasible alternative to the large, monolithic uniprocessors that dominate today’s microprocessor marketplace. Hydra offers a promising way to build a small-scale MP-on-a-chip using a fairly simple design that still maintains excellent performance on a wide variety of applications. This report examines key parts of the Hydra design — the memory hierarchy, the on-chip buses, and the control and arbitration mechanisms — and explains the rationale for some of the decisions made in the course of finalizing the design of this memory system, with particular emphasis given to applications that stress the memory system with numerous memory accesses. With the balance between complexity and performance that we obtain, we feel Hydra offers a promising model for future MP-on-a-chip designs.