  The PERCS system was designed by IBM in response to a DARPA challenge that
called for a high-productivity high-performance computing system. The IBM PERCS
architecture is a two level direct network having low diameter and high
bisection bandwidth. Mapping and routing strategies play an important role in
the performance of applications on such a topology. In this paper, we study
mapping strategies for PERCS architecture, that examine how to map tasks of a
given job on to the physical processing nodes. We develop and present
fundamental principles for designing good mapping strategies that minimize
congestion. This is achieved via a theoretical study of some common
communication patterns under both direct and indirect routing mechanisms
supported by the architecture.
