The Institute for Simulation Techniques and Scientific Computing of the University of Siegen develops a code for fluid dynamic called Ateles. The code is written in Fortran and showed already good performance on HPC systems in the past. The code was now extended by new features which where analysed within a POP performance audit. Several issues related to the serial code performance were identified there and a performance plan on how theses issues could be resolved was set up.

In a proof-of-concept study the POP experts verified, that the proposed code optimizations lead to a significant performance improvement. The optimizations include:

• Inlining of very short functions with high call rates
• Parameter and variable redefinitions that allow the reduction of expensive CPU operations like divisions

With these optimizations applied to the real code, we measured for the provided test case a performance increase of nearly 50% and the user was able to confirm a substantial performance improvement for his production runs.