IDEFIX: A versatile performance-portable Godunov code for astrophysical flows

Context. The exascale super-computers becoming available rely on hybrid energy-efficient architectures that involve an accelerator such as a graphics processing unit (GPU). Leveraging the computational power of these machines often means a significant rewrite of the numerical tools each time a new architecture becomes available.
Aims: We present IDEFIX, a new code for astrophysical flows that relies on the KOKKOS meta-programming library to guarantee performance portability on a wide variety of architectures while keeping the code as simple as possible to the user.
Methods: IDEFIX is based on a Godunov finite-volume method that solves the nonrelativistic hydrodynamical (HD) and magnetohy-drodynamical (MHD) equations on various grid geometries. IDEFIX includes a large choice of solvers and several additional modules (constrained transport, orbital advection, nonideal MHD), allowing users to address complex astrophysical problems.
Results: IDEFIX has been successfully tested on Intel and AMD CPUs (up to 131 072 CPU cores on Irene-Rome at TGCC) as well as NVidia and AMD GPUs (up to 1024 GPUs on Adastra at CINES). IDEFIX achieves more than 10⁸ cell s⁻¹ in MHD on a single NVidia V100 GPU and 3 × 10¹¹ cell s⁻¹ on 256 Adastra nodes (1024 GPUs) with 95% parallelization efficiency (compared to single node). For the same problem, IDEFIX is up to six times more energy efficient on GPUs compared to Intel Cascade Lake CPUs.
Conclusions: IDEFIX is now a mature exascale-ready open-source code that can be used on a large variety of astrophysical and fluid dynamics applications.