Problems with Comparing Interconnection Networks: Is an Alligator Better Than an Armadillo?

• Authors: Kathy J. Liszka;John K. Antonio;Howard Jay Siegel
• Venue: IEEE Parallel & Distributed Technology: Systems & Technology
• Year: 1997

Designing a parallel machine would be much easier if one inter-connection network were "best" for all applications and all operating environments (including hardware, software, and financial factors). Unfortunately, no such network exists. Furthermore, even for a fixed application domain and a fixed operating environment, selecting the best network may be difficult because many cost and performance metrics could be used. Suppose someone asked you to select the best animal. What features would you use to compare, say, an alligator and an armadillo? In some ways, the two are very similar: both have four legs, a rugged exterior, and sharp claws. However, in other ways the two are very different: one prefers a marshy environment, the other dry land; one has a long tail, the other a short tail; one is a reptile, the other a mammal. Which of the two, then, is a better animal and what makes it better? These questions apply to interconnection networks as well. Suppose you are comparing the average message delay, for a given set of traffic conditions, for a hypercube network and a mesh network. do you incorporate that hypercube networks may require more complex hardware? Should the total path width of all the links the networks employ be the same? Or should the two networks require the same number of transistors per switch? This article explores the problems of determining which metrics or weighted set of metrics designers should use to compare networks and how they should apply these metrics to yield meaningful information. The authors also look at problems in conducting fair and scientific evaluations.