调度器使用了两个优先级数组，即活动数组和过期数组，可以通过指针来访问它们。
The scheduler USES two priority arrays, namely active and expired arrays, that are accessed through Pointers.
内核为每个处理器维护两个 runqueue（过期的和活动的 runqueue）。
The 2.6 kernel maintains a pair of runqueues for each processor (the expired and active runqueues).
任务分时间片执行，在使用它们分配到的时间片时，这些任务被从活动的runqueue移至过期的runqueue。
Tasks are given time slices for execution, and when they use their allocation of time slice, they're moved from the active runqueue to the expired runqueue.
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