Low copy message passing on the Alliant CAMPUS/800

With modern massively parallel processors consisting of hundreds of RISC (reduced instruction set computer) processors, a significant portion of program run time is being spent in passing messages between processors. The authors address the problem of reducing unnecessary copies in message passing protocols. Message passing that avoids using copies in the application program and the transport mechanism is called low copy message passing. The authors describe the low copy message passing library on the Alliant CAMPUS/800 system. First, a way to reduce the number of copies in a message passing protocol is proposed. In gross machine independent terms, the message passing protocol can be reduced from seven major steps to one. The authors then describe how application programmers can use the low copy message passing library. Finally, a brief survey of applications is presented which shows how applications use the low copy library