Supporting Systolic and Memory Communication in iWarp Shekhar Borkar, Robert Cohn, George Cox, Thomas Gross, H. T. Kung, Monica Lam, Margie Levine, Brian Moore, Wire Moore, Craig Peterson, Jim Susman, Jim Sutton, John Urbanski, and Jon Webb December 11, 1990 CMU-CS-90-197 School of Computer Science Intel Corporation, CO4-01 Carnegie Mellon University 5200 N.E. Elam Young Pkwy Pittsburgh, Pennsylvania 15213 Hillsboro, Oregon 97124 Abstract TM iWarp is a parallel architecture developed jointly by Carnegie Mellon University and Intel Corporation. The iWarp communication system supports two widely used interprocessor communication styles: memory communication and systolic communication. This paper describes the rationale, architecture, and implementation for the iWarp communication system. The sending or receiving processor of a message can perform either memory or systolic communication. In memory communication, the entire message is buffered in the local memory of the processor before it is transmitted or after it is received. Therefore communication begins or terminates at the local memory. For conventional message passing methods, both sending and receiving processors use memory communication. In systolic communication, individual data items are transferred as they are produced, or are used as they are received, by the program running at the processor. Memory communication is flexible and well suited for general computing; whereas systolic communication is efficient and well suited for speed critical applications. A major achievement of the iWarp effort is the derivation of a common design to satisfy the requirements of both systolic and memory communication styles. This is made possible by two important innovations in communication: (1) program access to communication and (2) logical channels. The former allows programs to access data as they are transmitted and to redirect portions of messages to different destinations efficiently. The latter increases the connectivity between the processors and guarantees communication bandwidth for classes of messages. These innovations have provided a focus for the iWarp architecture. The result is a communication system that provides a total bandwidth of 320 MBytes/sec and that is integrated on a single VLSI component with a 20 MFLOPS plus 20 MIPS long instruction word computation engine. iWarp is a trademark of Intel Corp.... Warp is a servicemark of Carnegie Mellon University. Authors' affiliations: R. Cohn, T. Gross, H. T. Kung, and J. Webb are with Carnegie Mellon University; S. Borkar, G. Cox, M. Levine, B. Moore, W. Moore, C. Peterson, J. Susman, J. Sutton, and J. Urbanski are with Intel; M. Lam, who was a Ph.D. student at Carnegie Mellon University, is now with Computer Systems Laboratory, Stanford University, Stanford, CA 94305. An earlier version of this paper appears in Proceedings of the 17th Annual International Symposium on Computer Architecture, Seattle, Washington, May 1990, pp. 70 - 81.