Improving the Performance of CP2K on the Cray XT

CP2K is a freely available and increasingly popular Density Functional Theory code for the simulation of a wide range of systems. It is heavily used on many Cray XT systems, including ‘HECToR’ in the UK and ‘Monte Rosa’ in Switzerland. We describe performance optimisations made to the code in several key areas, including 3D Fourier Transforms, and present the implementation of a load balancing scheme for multi-grids. These result in performance gains of around 30% on 256 cores (for a generally representative benchmark) and up to 300% on 1024 cores (for non-homogeneous systems). Early results from the implementation of hybrid MPI/OpenMP parallelism in the code are also presented.