ORB5 is a global, gyrokinetic, Lagrangian, Particle-In-Cell (PIC), finite element, electromagnetic, GPU-enabled code developed at SPC, with important contributions from the Max-Planck IPP in Garching and Greifswald and the University of Warwick. The ORB5 code features [1-8]
On the numerical side, the ORB5 code has been completely refactored in 2016-2018, with a new data structure and its parallelism enhanced, partly under a PASC Co-design project. Originally a pure MPI code based on domain decomposition and domain cloning, it now features:
- hybrid MPI/OpenMP and MPI/OpenACC parallel programming models
- various multithreading algorithmic options for the various kernels, in particular for the gyro-averaged charge and current deposition and field assignment
- single master source code encompassing all functionalities mentioned above, and which can be run either on CPU-only or on GPU-equipped HPC systems.
The GPU is really accelerating the code. For an electromagnetic simulation, the code runs 4 times faster when using the GPU than when using the 12-core CPUs on the Piz Daint Cray XC50 at CSCS. For a large dataset, running ORB5 on 512 nodes with GPU is 1.5 times faster than running on 2048 nodes without using the GPU, the amount of resources (node-hours) to get to the solution is reduced by a factor of 6, and the energy-to-solution reduced by a factor 8.5.
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