Tuning means to change some system variables/configurations (without changing the program itself) in order to optimize the performance.

• Use subroutine profiling to focus the efforts on tuning specific procedures and improve the program's performance.

• Use profiling tools such as prof, gprof and line-by-line profilers.
• Define Amdahl's Law.
• Tune a parallel program in order to achieve better runtimes and to optimize the usage of the HPC resources.

• PE4.1-B Tuning without Building a Parallel Program
• PE4.2-B Tuning without Modifying the Source Code
• PE4.3-B Tuning via Reprogramming
• K2.1-B Performance Frontiers