NDIS高手求教，关于SPIN LOCK的应用？

关于SPIN LOCK的应用不是太了解，
Attempted acquisition of a spin lock temporarily raises the IRQL of the requesting thread to the IRQL associated with the spin lock. This prevents all lower IRQL threads on the same processor from preempting the executing thread. Threads, on the same processor, running at a higher IRQL can preempt the executing thread, but these threads cannot acquire the spin lock because it has a lower IRQL.

这段话如何理解？？  这在DDK里面。

大概的意思是当请求了spin lock之后，IRQL的值会提升了，而释放spin lock之后就会降低IRQL，而在获得spin lock的期间要注意一些函数的运行IRQL