Accelerating Sparse Linear Solvers in OpenFOAM using RISC-V Vector Extensions

Abstract

Computational Fluid Dynamics (CFD) relies heavily on the efficiency of linear solvers based on sparse linear algebra kernels. Widely used frameworks like OpenFOAM exploit parallelism primarily at the domain decomposition level via MPI. Support for vector/SIMD architectures is limited to compiler auto-vectorization. Furthermore, support for such architectures is limited by OpenFOAM's internal matrix data format, which is intrinsically ill-suited for the contiguous memory accesses required for efficient execution on vector processors. In this work, we focused on two very different RISC-V architectures: the prototype long-vector EPAC accelerator and the commercial short-vector CPU Sophon SG2044. On these platforms, we optimized the Sparse Matrix-Vector multiplication (SpMV) using RISC-V vector intrinsics and integrated it into a custom smoother, performing a runtime conversion of internal data into a vector-friendly format. Experimental results on the EPAC test chip show a 6x speedup for the smoother; benchmarks on Monte Cimone (MCv2) cluster with the Sophon SG2044 processor achieve a 1.5x smoother speedup, proving that legacy CFD codes can be effectively accelerated on both research and commercial emerging hardware.