GPU Implementation of a Sophisticated Implicit Low-Order Finite Element Solver with FP21-32-64 Computation Using OpenACC

Accelerating applications with portability and maintainability is one of the big challenges in science and engineering. Previously, we have developed a fast implicit low-order three-dimensional finite element solver, which has a complicated algorithm including artificial intelligence and transprecision computing. In addition, all possible tunings for the target architecture were implemented; accordingly, the solver has inferior portability and maintainability. In this paper, we apply OpenACC to the solver. The directive-based implementation of OpenACC enables GPU computation to be introduced with a smaller developmental cost even for complex codes. In performance measurements on AI Bridging Cloud Infrastructure (ABCI), we evaluated that a reasonable speedup was attained on GPUs, given that the elapsed time of the entire solver was reduced to 1/14 of that on CPUs based on the original CPU implementation. Our proposed template to use transprecision computing with our custom FP21 data type is available to the public; therefore, it can provide a successful example for other scientific computing applications.