Prediction of the Inter-Node Communication Costs of a New Gyrokinetic Code with Toroidal Domain

We consider the communication costs of gyrokinetic plasma physics simulations running at large scale. For this we apply virtual decompositions of the toroidal domain in three dimensions and additional domain cloning to existing simulations done with the ORB5 code. The communication volume and the number of communication partners per timestep for every virtual task (node) are evaluated for the particles and the structured mesh. Thus the scaling properties of a code with the new domain decompositions are derived for simple models of a modern computer network and corresponding processing units. The effectiveness of the suggested decomposition has been shown. For a typical simulation with 2 . 10(9) particles and a mesh of 256 x 1024 x 512 grid points scaling to 2, 800 nodes should be achieved.