Commit edde96ea authored by Pekka Enberg's avatar Pekka Enberg Committed by Thomas Gleixner

sched: Document schedule() entry points

This patch adds a comment on top of the schedule() function to explain
to scheduler newbies how the main scheduler function is entered.
Acked-by: default avatarRandy Dunlap <rdunlap@xenotime.net>
Explained-by: default avatarIngo Molnar <mingo@kernel.org>
Explained-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarPekka Enberg <penberg@kernel.org>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1344070187-2420-1-git-send-email-penberg@kernel.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 532b1858
...@@ -3367,6 +3367,40 @@ pick_next_task(struct rq *rq) ...@@ -3367,6 +3367,40 @@ pick_next_task(struct rq *rq)
/* /*
* __schedule() is the main scheduler function. * __schedule() is the main scheduler function.
*
* The main means of driving the scheduler and thus entering this function are:
*
* 1. Explicit blocking: mutex, semaphore, waitqueue, etc.
*
* 2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return
* paths. For example, see arch/x86/entry_64.S.
*
* To drive preemption between tasks, the scheduler sets the flag in timer
* interrupt handler scheduler_tick().
*
* 3. Wakeups don't really cause entry into schedule(). They add a
* task to the run-queue and that's it.
*
* 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:
*
* - If the kernel is preemptible (CONFIG_PREEMPT=y):
*
* - in syscall or exception context, at the next outmost
* preempt_enable(). (this might be as soon as the wake_up()'s
* spin_unlock()!)
*
* - in IRQ context, return from interrupt-handler to
* preemptible context
*
* - If the kernel is not preemptible (CONFIG_PREEMPT is not set)
* then at the next:
*
* - cond_resched() call
* - explicit schedule() call
* - return from syscall or exception to user-space
* - return from interrupt-handler to user-space
*/ */
static void __sched __schedule(void) static void __sched __schedule(void)
{ {
......
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