Tackling exascale systems for astrophysics

Abstract Exascale systems are now appearing in the US, Japan, in Europe with two exascale procurements in the coming years and very likely in China. These systems offer great opportunities for the numerical astrophysics community and also raise serious technical challenges. Many legacy codes need to be fully rewritten to benefit from exascale architectures. Performance portability is a key issue as well as the management of the huge amount of data generated by exascale simulations. In this paper we discuss the path we have chosen to exascale and the software engineering solution chosen to address performance portability in the long run and data management. A new radiation hydrodynamics code based on the Kokkos library is presented as well as test runs and preliminary performance analysis. The first target of this new code will be to study supernova ejecta. They are multidimensional fluids, structured on both small and large scales following the non-linear development of complex fluid instabilities during and after the explosion. They contain a wealth of information about stellar composition and the evolution of elements in the interstellar medium. Their study requires significant computing resources that can be met through the use of exascale machines and suitable software.