Commit 967fc046 authored by Gregory Haskins's avatar Gregory Haskins
Browse files

sched: add sched_class->needs_post_schedule() member 



We currently run class->post_schedule() outside of the rq->lock, which
means that we need to test for the need to post_schedule outside of
the lock to avoid a forced reacquistion.  This is currently not a problem
as we only look at rq->rt.overloaded.  However, we want to enhance this
going forward to look at more state to reduce the need to post_schedule to
a bare minimum set.  Therefore, we introduce a new member-func called
needs_post_schedule() which tests for the post_schedule condtion without
actually performing the work.  Therefore it is safe to call this
function before the rq->lock is released, because we are guaranteed not
to drop the lock at an intermediate point (such as what post_schedule()
may do).

We will use this later in the series

[ rostedt: removed paranoid BUG_ON ]

Signed-off-by: default avatarGregory Haskins <ghaskins@novell.com>
parent 8f45e2b5

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1012,6 +1012,7 @@ struct sched_class { 
			      struct rq *busiest, struct sched_domain *sd,

			      enum cpu_idle_type idle);

	void (*pre_schedule) (struct rq *this_rq, struct task_struct *task);

	int (*needs_post_schedule) (struct rq *this_rq);

	void (*post_schedule) (struct rq *this_rq);

	void (*task_wake_up) (struct rq *this_rq, struct task_struct *task);

kernel/sched.c

+7 −1
Original line number Diff line number Diff line
@@ -2621,6 +2621,12 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev) 
{

	struct mm_struct *mm = rq->prev_mm;

	long prev_state;

#ifdef CONFIG_SMP

	int post_schedule = 0;



	if (current->sched_class->needs_post_schedule)

		post_schedule = current->sched_class->needs_post_schedule(rq);

#endif



	rq->prev_mm = NULL;
@@ -2639,7 +2645,7 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev) 
	finish_arch_switch(prev);

	finish_lock_switch(rq, prev);

#ifdef CONFIG_SMP

	if (current->sched_class->post_schedule)

	if (post_schedule)

		current->sched_class->post_schedule(rq);

#endif

kernel/sched_rt.c

+14 −10
Original line number Diff line number Diff line
@@ -1290,21 +1290,24 @@ static void pre_schedule_rt(struct rq *rq, struct task_struct *prev) 
		pull_rt_task(rq);

}



/*

 * assumes rq->lock is held

 */

static int needs_post_schedule_rt(struct rq *rq)

{

	return rq->rt.overloaded ? 1 : 0;

}



static void post_schedule_rt(struct rq *rq)

{

	/*

	 * If we have more than one rt_task queued, then

	 * see if we can push the other rt_tasks off to other CPUS.

	 * Note we may release the rq lock, and since

	 * the lock was owned by prev, we need to release it

	 * first via finish_lock_switch and then reaquire it here.

	 * This is only called if needs_post_schedule_rt() indicates that

	 * we need to push tasks away

	 */

	if (unlikely(rq->rt.overloaded)) {

	spin_lock_irq(&rq->lock);

	push_rt_tasks(rq);

	spin_unlock_irq(&rq->lock);

}

}



/*

 * If we are not running and we are not going to reschedule soon, we should
@@ -1557,6 +1560,7 @@ static const struct sched_class rt_sched_class = { 
	.rq_online              = rq_online_rt,

	.rq_offline             = rq_offline_rt,

	.pre_schedule		= pre_schedule_rt,

	.needs_post_schedule	= needs_post_schedule_rt,

	.post_schedule		= post_schedule_rt,

	.task_wake_up		= task_wake_up_rt,

	.switched_from		= switched_from_rt,

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