Journal Article

Accelerating <span class="smallCaps">nbody</span>6 with graphics processing units

Keigo Nitadori and Sverre J. Aarseth

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 424, issue 1, pages 545-552
Published in print July 2012 | ISSN: 0035-8711
Published online July 2012 | e-ISSN: 1365-2966 | DOI:
Accelerating nbody6 with graphics processing units

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We describe the use of graphics processing units (GPUs) for speeding up the code nbody6 which is widely used for direct N-body simulations. Over the years, the N2 nature of the direct force calculation has proved a barrier for extending the particle number. Following an early introduction of force polynomials and individual time steps, the calculation cost was first reduced by the introduction of a neighbour scheme. After a decade of GRAPE computers which speeded up the force calculation further, we are now in the era of GPUs where relatively small hardware systems are highly cost effective. A significant gain in efficiency is achieved by employing the GPU to obtain the so-called regular force which typically involves some 99 per cent of the particles, while the remaining local forces are evaluated on the host. However, the latter operation is performed up to 20 times more frequently and may still account for a significant cost. This effort is reduced by parallel SSE/AVX procedures where each interaction term is calculated using mainly single precision. We also discuss further strategies connected with coordinate and velocity prediction required by the integration scheme. This leaves hard binaries and multiple close encounters which are treated by several regularization methods. The present nbody6–gpu code is well balanced for simulations in the particle range 104–2 × 105 for a dual-GPU system attached to a standard PC.

Keywords: methods: numerical; globular clusters: general

Journal Article.  5446 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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