Performance analysis of direct N-body algorithms on special-purpose supercomputers

Direct-summation N-body algorithms compute the gravitational interaction between stars in an exact way and have a computational complexity of O(N-2). Performance call be greatly enhanced via the use of special-purpose accelerator boards like the GRAPE-6A. However, the memory of the GRAPE boards is limited. Here, we present a performance analysis of direct N-body codes oil two parallel supercomputers that incorporate special-purpose boards, allowing as many as four million particles to be integrated. Both computers employ high-speed, Infiniband interconnects to minimize communication overhead, which call otherwise become significant due to the small number of "active" particles at each time step. We find that the computation time scales well with processor number; for 2 x 106 particles, efficiencies greater than 60% and speeds in excess of similar to 3 TFlops are reached. (c) 2006 Elsevier B.V. All rights reserved.