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Commit 11dc76f0 authored by Linus Torvalds's avatar Linus Torvalds
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Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull scheduler fix from Ingo Molnar:
 "Update the <linux/swait.h> documentation to discourage their use"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/swait: Document it clearly that the swait facilities are special and shouldn't be used
parents 02c7dfc0 88796e7e

include/linux/swait.h

+16 −11
Original line number Diff line number Diff line
@@ -9,13 +9,16 @@ 
/*

 * Simple wait queues

 *

 * While these are very similar to the other/complex wait queues (wait.h) the

 * most important difference is that the simple waitqueue allows for

 * deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold

 * times.

 * While these are very similar to regular wait queues (wait.h) the most

 * important difference is that the simple waitqueue allows for deterministic

 * behaviour -- IOW it has strictly bounded IRQ and lock hold times.

 *

 * In order to make this so, we had to drop a fair number of features of the

 * other waitqueue code; notably:

 * Mainly, this is accomplished by two things. Firstly not allowing swake_up_all

 * from IRQ disabled, and dropping the lock upon every wakeup, giving a higher

 * priority task a chance to run.

 *

 * Secondly, we had to drop a fair number of features of the other waitqueue

 * code; notably:

 *

 *  - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;

 *    all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
@@ -24,12 +27,14 @@ 
 *  - the exclusive mode; because this requires preserving the list order

 *    and this is hard.

 *

 *  - custom wake functions; because you cannot give any guarantees about

 *    random code.

 *

 * As a side effect of this; the data structures are slimmer.

 *  - custom wake callback functions; because you cannot give any guarantees

 *    about random code. This also allows swait to be used in RT, such that

 *    raw spinlock can be used for the swait queue head.

 *

 * One would recommend using this wait queue where possible.

 * As a side effect of these; the data structures are slimmer albeit more ad-hoc.

 * For all the above, note that simple wait queues should _only_ be used under

 * very specific realtime constraints -- it is best to stick with the regular

 * wait queues in most cases.

 */



struct task_struct;