Bonsai: A GPU Tree-Code

We present a gravitational hierarchical N-body code that is designed to run efficiently on Graphics Processing Units (GPUs). All parts of the algorithm are exectued on the GPU which eliminates the need for data transfer between the Central Processing Unit (CPU) and the GPU. Our tests indicate that the gravitational tree-code outperforms tuned CPU code for all parts of the algorithm and show an overall performance improvement of more than a factor 20, resulting in a processing rate of more than 2.8 million particles per second.