Imbalance or Serial Spin time is wall time when working threads are spinning on a synchronization barrier consuming CPU resources. High metric value on parallel regions can be caused by load imbalance or inefficient concurrency of all working threads. To address load imbalance, consider applying dynamic work scheduling. High metric value on serial execution (Serial - outside any region) can indicate that serial application time is significant and limiting efficient processor utilization. Explore options for parallelization, algorithm or microarchitecture tuning of the serial part of the application.