A fraction of Serial time in a parallel application is one of the factors that limits application scalability, which is an ability of the application to utilize available hardware resources, such as cores, for executing the application code. Accoring to Amdahl's law, the maximum speed-up for a parallel application, where P is a parallel portion of the application execution and N is a number of processor elements, is 1/((1-P)+(P/N)). So, the more (1-P) - a serial part of the application execution, - the further you are from a linear speed-up with a growing number of N - a number of processor elements - being limited with the serial part of execution.
When your application is parallelized with OpenMP, the sequential code execution may be a result of the code executed out of OpenMP regions or executed inside
#pragma omp master
#pragma omp single
constructs. This recipe focuses on the first case detection. Consider following these steps to detect the time of the code executed outside of OpenMP regions, analyze the distribution on serial hotspot functions/loops, and understand opportunities for code parallelization with the Intel® VTune™ Amplifier.