DescriptionAccurate prediction of fluid flows remains an important field of research and engineering. To this end, computational fluid dynamics is widely employed. Due to their high demands on computational resources CFD applications profit from HPC systems. Continuous performance analysis and optimization is key to efficient utilization of HPC resources. This paper demonstrates the beneficial cooperation between developers of HPC software and performance tools in the context of the CFD solver CODA and the sparse linear system solver Spliss. We investigate concepts used by CODA/Spliss to achieve high scalability, evaluate their effectiveness with performance analysis tools, and illustrate profits obtained from a close collaboration between HPC application and tool developers. Tools support developers in analyzing/tuning their applications. Feedback and requests of developers inspire tools enhancements. We highlight these aspects with an extended support of non-blocking collectives in performance tools and emphasize the need for sophisticated tool support of multi-threaded MPI applications.