arXiv subjects

Tilman Dannert

Publications and source records attributed to Tilman Dannert.

3 recordsLinked to original sources

arXiv2026

Multi-GPU Hybrid Particle-in-Cell Monte Carlo Simulations for Exascale Computing Systems

Particle-in-Cell (PIC) Monte Carlo (MC) simulations are central to plasma physics but face increasing challenges on heterogeneous HPC systems due to excessive data movement, synchronization overheads, and inefficient utilization of multiple accelerators. In this work, we present a portable, multi-GPU hybrid MPI+OpenMP implementation of BIT1 that enables scalable execution on both Nvidia and AMD accelerators through OpenMP target tasks with explicit dependencies to overlap computation and communication across devices. Portability is achieved through persistent device-resident memory, an optimized contiguous one-dimensional data layout, and a transition from unified to pinned host memory to improve large data-transfer efficiency, together with GPU Direct Memory Access (DMA) and runtime interoperability for direct device-pointer access. Standardized and scalable I/O is provided using openPMD and ADIOS2, supporting high-performance file I/O, in-memory data streaming, and in-situ analysis and visualization. Performance results on pre-exascale and exascale systems, including Frontier (OLCF-5) for up to 16,000 GPUs, demonstrate significant improvements in run time, scalability, and resource utilization for large-scale PIC MC simulations.

physics.plasm-ph↗

arXiv2025

A high-performance elliptic solver for plasma boundary turbulence codes

Elliptic equations play a crucial role in turbulence models for magnetic confinement fusion. Regardless of the chosen modeling approach - whether gyrokinetic, gyrofluid, or drift-fluid - the Poisson equation and Amp\`{e}re's law lead to elliptic problems that must be solved on 2D planes perpendicular to the magnetic field. In this work, we present an efficient solver for such generalised elliptic problems, especially suited for the conditions in the boundary region. A finite difference discretisation is employed, and the solver is based on a flexible generalised minimal residual method (fGMRES) with a geometric multigrid preconditioner. We present implementations with OpenMP parallelisation and GPU acceleration, with backends in CUDA and HIP. On the node level, significant speed-ups are achieved with the GPU implementation, exceeding external library solutions such as rocALUTION. In accordance with theoretical scaling laws for multigrid methods, we observe linear scaling of the solver with problem size, $O(N)$. This solver is implemented in the PARALLAX/PAccX libraries and serves as a central component of the plasma boundary turbulence codes GRILLIX and GENE-X.

physics.plasm-ph↗

arXiv2013

Porting Large HPC Applications to GPU Clusters: The Codes GENE and VERTEX

We have developed GPU versions for two major high-performance-computing (HPC) applications originating from two different scientific domains. GENE is a plasma microturbulence code which is employed for simulations of nuclear fusion plasmas. VERTEX is a neutrino-radiation hydrodynamics code for "first principles"-simulations of core-collapse supernova explosions. The codes are considered state of the art in their respective scientific domains, both concerning their scientific scope and functionality as well as the achievable compute performance, in particular parallel scalability on all relevant HPC platforms. GENE and VERTEX were ported by us to HPC cluster architectures with two NVidia Kepler GPUs mounted in each node in addition to two Intel Xeon CPUs of the Sandy Bridge family. On such platforms we achieve up to twofold gains in the overall application performance in the sense of a reduction of the time to solution for a given setup with respect to a pure CPU cluster. The paper describes our basic porting strategies and benchmarking methodology, and details the main algorithmic and technical challenges we faced on the new, heterogeneous architecture.

physics.comp-ph↗