Efficient data layouts for a three-dimensional electrostatic Particle-in-Cell code

The paper presents extensions in 3d of our preliminary 2d results (Barsamian et al., 2017), with highlights on the difficulties and solutions proposed for these extensions. Specifically, our main contributions consist in proposing a new space-filling curve in 3d (called L6D) to improve the cache reuse and an adapted loop transformation (strip-mining) to achieve efficient vectorization. The analysis of these optimization strategies is performed in two-stages, first on a 24-core socket and second on a super-computer, from 1 to 3072 cores, demonstrating significant performance gains and very satisfactory weak scaling results of the code.