How is the Scheduler Called?

How is the Scheduler Called?

__schedule() is the main scheduler function.

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* The main means of driving the scheduler and thus entering this function are:

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*   1. Explicit blocking: mutex, semaphore, waitqueue, etc.

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*   2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return

*      paths. For example, see arch/x86/entry_64.S.

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*      To drive preemption between tasks, the scheduler sets the flag in timer

*      interrupt handler scheduler_tick().

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*   3. Wakeups don't really cause entry into schedule(). They add a

*      task to the run-queue and that's it.

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*      Now, if the new task added to the run-queue preempts the current

*      task, then the wakeup sets TIF_NEED_RESCHED and schedule() gets

*      called on the nearest possible occasion: