Performance optimisation of the parallel CFD code MGLET across different HPC platforms

This paper presents the optimisation techniques implemented to run across four HPC platforms the finite-volume computational fluid dynamics (CFD) code MGLET (Multi Grid Large Eddy Turbulence). We analysed and applied refactoring to the parallel communication routines, and reduced the memory footprint significantly, resulting in a substantial improvement of the parallel-scaling capability and in an increase of the maximum number of degrees of freedom for applications. Data structures and files layout were redesigned for implementing parallel I/O in HDF5. The new parallel I/O strategy results in a considerable increase in the average data transfer rate compared with the former serial implementation. An I/O pattern analysis and detailed I/O profiling of the new implementation were then conducted and further performance improvement was achieved by increasing the size of I/O requests and reducing the number of I/O processes. We compare the improved parallel-scaling capability of MGLET on different architectures using representative CFD application test cases.