CCL - A PORTABLE AND TUNABLE COLLECTIVE COMMUNICATION LIBRARY FOR SCALABLE PARALLEL COMPUTERS

A collective communication library for parallel computers includes fre quently used operations such as broadcast, reduce, scatter, gather, co ncatenate, synchronize, and shift. Such a library provides users with a convenient programming interface, efficient communication operations , and the advantage of portability. A library of this nature, the Coll ective Communication Library (CCL), intended for the line of scalable parallel computer products by IBM, has been designed. CCL is part of t he parallel application programming interface of the recently announce d IBM 9076 Scalable POWERparallel System 1 (SP1). In this paper, we ex amine several issues related to the functionality, correctness, and pe rformance of a portable collective communication library while focusin g on three novel aspects in the design and implementation of CCL: 1) t he introduction of process groups, 2) the definition of semantics that ensures correctness, and 3) the design of new and tunable algorithms based on a realistic point-to-point communication model.