Performance characteristics of a parallel treecode

I describe here the performances of a parallel treecode with individual particle timesteps. The code is based on the Barnes-Hut algorithm and runs cosmological N-body simulations on parallel machines with a distributed memory architecture using the MPI message passing library. For a configuration with a constant number of particles per processor the scalability of the code has been tested up to P=32 processors. The average CPU time per processor necessary for solving the gravitational interactions is within $\sim 10$ of that expected from the ideal scaling relation. The load balancing efficiency is high ($\simgt90$) if the processor domains are determined every large timestep according to a weighting scheme which takes into account the total particle computational load within the timestep.