SMP_LNGSPINWAIT is a system parameter that establishes, in 10-microsecond intervals, the amount of time a CPU in an SMP system normally waits for access to a shared resource. This process is called spinwaiting. Generally spinlocks at IPL <= 8 have long holding times, therefore have their timeout intervals set to SMP_LNGSPINWAIT to prevent SPINWAIT timeouts in cases of nested acquisition. A timeout causes a CPUSPINWAIT bugcheck. The default value is 3000000 (30,00, 000 10-microsecond intervals or 30 second).