Imbalance or Serial Spinning time is CPU time when working threads are spinning on a synchronization barrier consuming CPU resources. This can be caused by load imbalance, insufficient concurrency for all working threads or waits on a barrier in the case of serialized execution.
The threading runtime function related to time spent on imbalance or serial spinning consumed a significant amount of CPU time. This can be caused by a load imbalance, insufficient concurrency for all working threads, or busy waits of worker threads while serial code is executed. If there is an imbalance, apply dynamic work scheduling or reduce the size of work chunks or tasks. If there is insufficient concurrency, consider collapsing the outer and inner loops. If there is a wait for completion of serial code, explore options for parallelization with Intel Advisor, algorithm, or microarchitecture tuning of the application's serial code with VTune Amplifier Hotspots or Microarchitecture Exploration analysis respectively. For OpenMP* applications, use the Per-Barrier OpenMP Potential Gain metric set in the HPC Performance Characterization analysis to discover the reason for high imbalance or serial spin time.