Presently, massively parallel processors (MPPs) are available only in a few
commercial models. A sequence of three ASCI Teraflops MPPs has appeared be
fore the new millenium. This paper evaluates six MPP systems through STAP b
enchmark experiments. The STAP is a radar signal processing benchmark which
exploits regularly structured SPMD data parallelism. We reveal the resourc
e scaling effects on MPP performance along orthogonal dimensions of machine
size, processor speed, memory capacity, messaging latency, and network ban
dwidth. We show how to achieve balanced resources Scaling against enlarged
workload (problem size). Among three commercial MPPs, the IBM SP2 shows the
highest speed and efficiency, attributed to its well-designed network with
middleware support for single system image. The Gray T3D demonstrates a hi
gh network bandwidth with a good NUMA memory hierarchy. The Intel Paragon t
rails far behind due to slow processors used and excessive latency experien
ced in passing messages. Our analysis projects the lowest STAP speed on the
ASCI Red, compared with the projected speed of two ASCI Blue machines. Thi
s is attributed to slow processors used in ASCI Red and the mismatch betwee
n its hardware and software. The Blue Pacific shows the highest potential t
o deliver scalable performance up to thousands of nodes. The Blue Mountain
is designed to have the highest network bandwidth. Our results suggest a li
mit on the scalability of the distributed shared-memory (DSM) architecture
adopted in Blue Mountain. The seating model offers a quantitative method to
match resource scaling with problem scaling to yield a truly scalable perf
ormance. The model helps MPP designers optimize the processors, memory, net
work, and I/O subsystems of an MPP. For MPP users, the scaling results can
be applied to partition a large workload for SPMD execution or to minimize
the software overhead in collective communication or remote memory update o
perations. Finally, our scaling model is assessed to evaluate MPPs with ben
chmarks other than STAP.