5. Summary

This document introduced a case of performance tuning of the commercial CFD application software (Application), whose source code is large and has complex structure.

The Application was too large and complex to be analyzed the entire application with fapp (Fujitsu Advanced Performance Profiler). Therefore, the execution time for each measurement region and the cost of the function using fipp (Fujitsu Instant Performance Profiler) was measured at first to narrow down functions or loops to be tuned. Then, based on the results of fapp measurements of the narrowed functions or loops and the analysis of the optimization messages during compilation, the tuning plan was determined.

Another difficulty was that the proportion of the cost of most functions in the Application was less than a few percent, so many functions needed to be tuned for obtaining the target performance. In the tuning, the top 30 functions with that cost (sum of their cost was about 52% of the entire Application) were analyzed and various types of tuning were performed to these functions. Additionally, tuning to improve the load balance between MPI processes of the Application and tuning of memory allocation functions that are used by many other functions were also performed. In fact, this increased tuning effort forced a review of tuning workplan, including adding staffs.

As a result of these effort, the target performance was achieved by improving performance rate of 58%, in other words, about 2.4 times speedup (execution time was improved from 202.9 seconds to 85.0 seconds) compared to the initial version.