DCAF is a directly connected arbitration free photonic crossbar that is realized by taking advantage of multiple photonic layers connected with photonic vias. In order to evaluate DCAF we developed a detailed implementation model for the network and analyzed the power and performance on a variety of benchmarks, including SPLASH-2 and synthetic traces. Our results demonstrate that the overhead required by arbitration is non-trivial, especially at high loads. Eliminating the need for arbitration, sizing the buffers carefully and retransmitting lost packets when there is contention results in a 44% reduction in average packet latency without additional power overhead. We also use an analytical model for ScaLAPACK QR decomposition and find that a 64 processor DCAF could outperform a 1024 node cluster connected with 40Gbps links on matrices up to 500MB in size.
['Christopher Nitta', 'Matthew K. Farrens', 'Venkatesh Akella']
DCAF - A Directly Connected Arbitration-Free Photonic Crossbar for Energy-Efficient High Performance Computing