SWITCH-PERIOD* - This variable helps determine how frequently threads switch control. When a thread executes SWITCH-PERIOD number of selected operations, the threads switch control. The selected operations are generally comparisons. Comparison operations are used to cause compute-bound threads to switch.
Setting the value of SWITCH-PERIOD lower will increase the overhead spent switching threads, but increase the uniformity of thread execution. Setting the value very low can significantly hurt performance. The default value is 500.