The Mit Alewife Machine: a Large-scale Distributed-memory Multiprocessor

The Alewife multiprocessor project focuses on the architecture and design of a large-scale parallel machine. The machine uses a low dimension direct interconnection network to provide scalable communication band-width, while allowing the exploitation of locality. Despite its distributed memory architecture, Alewife allows eecient shared memory programming through a multilayered approach to locality management. A new scalable cache coherence scheme called LimitLESS directories allows the use of caches for reducing communication latency and network bandwidth requirements. Alewife also employs run-time and compile-time methods for partitioning and placement of data and processes to enhance communication locality. While the above methods attempt to minimize communication latency, remote communication with distant processors cannot be completely avoided. Alewife's processor, Sparcle, is designed to tolerate these latencies by rapidly switching between threads of computation. This paper describes the Alewife architecture and concentrates on the novel hardware features of the machine including LimitLESS directories and the rapid context switching processor.