ExaSlang: a domain-specific language for highly scalable multigrid solvers

High-Performance Computing (HPC) systems are becoming increasingly parallel and heterogeneous. As a consequence, HPC applications, such as simulation software, need to be especially designed towards these systems to achieve optimal performance. This, in turn, leads to higher complexity, making software engineers and scientists require a deep knowledge of the hardware and its technologies. As a remedy, domain-specific languages (DSLs) are a convenient technology for domain experts to describe settings and problems they want to solve using terms and models familiar to them. This specification is transformed into a target language, i. e., source code in another programming language or a binary executable, by a specialized compiler. We propose ExaSlang, a language for the specification of numerical solvers based on the multigrid method targeting distributed-memory systems. Furthermore, we present the transformation framework that drives the corresponding source-to-source compiler. It emits C++ code utilizing a hybrid OpenMP and MPI parallelization. Moreover, we substantiate our approach with scaling results of our code scaling up to the complete JUQUEEN cluster, consisting of 28,672 nodes, with a total of 458,752 cores.