SMP_LNGSPINWAIT 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).