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sched/core: Explain sleep/wakeup in a better way

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There were a few questions wrt. how sleep-wakeup works. Try and explain
it more.

Requested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2016-10-19 15:45:27 +02:00
committed by Ingo Molnar
parent 3c3fcb45d5
commit a225023828
2 changed files with 44 additions and 23 deletions
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15
kernel/sched/core.c
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@@ -1995,14 +1995,15 @@ static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
* @state: the mask of task states that can be woken
* @wake_flags: wake modifier flags (WF_*)
*
* Put it on the run-queue if it's not already there. The "current"
* thread is always on the run-queue (except when the actual
* re-schedule is in progress), and as such you're allowed to do
* the simpler "current->state = TASK_RUNNING" to mark yourself
* runnable without the overhead of this.
* If (@state & @p->state) @p->state = TASK_RUNNING.
*
* Return: %true if @p was woken up, %false if it was already running.
* or @state didn't match @p's state.
* If the task was not queued/runnable, also place it back on a runqueue.
*
* Atomic against schedule() which would dequeue a task, also see
* set_current_state().
*
* Return: %true if @p->state changes (an actual wakeup was done),
* %false otherwise.
*/
static int
try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)