Supporting sets of arbitrary connections on iWarp 
              through communication context switches


  Anja Feldmann        Thomas M. Stricker        Thomas E. Warfel

                   School of Computer Science
                   Carnegie Mellon University
                   Pittsburgh, PA 15213-3890


Abstract                                                               
                                                                       
In this paper we introduce the ConSet communication model for
distributed memory parallel computers. The communication needs
of an application program can be satisfied by some arbitrary set of
connections which are partitioned into discrete phases. A commu-
nication context switch is used to select the active phase.

   We present an implementation of the ConSet model on the iWarp
and describe its performance characteristics, contrasting it to a mes-
sage passing implementation on the same machine. Our implemen-
tation demonstrates how one existing parallel computer can function
as a "reconfigurable network" without needing a new processor in-
terconnect technology.
                                                                       
   The ConSet model works best when communication patterns can
be optimized at compile time. We examine the interactions of the
target architecture with the algorithmic problems encountered de-
signing a communication compiler to effectively partition, route,
and schedule connections. We built a prototype communication
compiler for our iWarp implementation, and are using it to generate
iWarp code. Looking at basic communication patterns as well as
patterns generated by an iterative finite element PDE solver, we
compare ConSet's performance (using the compiler's schedules) to
that of message passing. Our experiments suggest that ConSet com-
munication offers a performance advantage over message passing in
applications where the communication pattern is known at compile
time.



Note: Reprint from the proceedings of the Fifth ACM Symposium on
Parallel Algorithms and Architectures SPAA93, July 1-4, 1993, Schloss
Velen, Westfalia, Germany.