Software versus hardware shared-memory implementation: a case study

Compares the performance of software-supported shared memory on a general-purpose network to hardware-supported shared memory on a dedicated interconnect. Up to eight processors, the results are based on the execution of a set of application programs on a SGI 4D/480 multiprocessor and on TreadMarks, a distributed shared memory system that runs on a Fore ATM LAN of DECstation-5000/240s. Since the DECstation and the 4D/480 use the same processor, primary cache, and compiler, the shared-memory implementation is the principal difference between the systems. Beyond eight processors, the results are based on execution-driven simulation. Specifically, the authors compare a software implementation on a general-purpose network of uniprocessor nodes, a hardware implementation using a directory-based protocol on a dedicated interconnect, and a combined implementation using software to provide shared memory between multiprocessor nodes with hardware implementing shared memory within a node