Commit d95f4122 authored by Mike Galbraith's avatar Mike Galbraith Committed by Ingo Molnar
Browse files

sched: Add yield_to(task, preempt) functionality 



Currently only implemented for fair class tasks.

Add a yield_to_task method() to the fair scheduling class. allowing the
caller of yield_to() to accelerate another thread in it's thread group,
task group.

Implemented via a scheduler hint, using cfs_rq->next to encourage the
target being selected.  We can rely on pick_next_entity to keep things
fair, so noone can accelerate a thread that has already used its fair
share of CPU time.

This also means callers should only call yield_to when they really
mean it.  Calling it too often can result in the scheduler just
ignoring the hint.

Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201095051.4ddb7738@annuminas.surriel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent ac53db59

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1058,6 +1058,7 @@ struct sched_class { 
	void (*enqueue_task) (struct rq *rq, struct task_struct *p, int flags);

	void (*dequeue_task) (struct rq *rq, struct task_struct *p, int flags);

	void (*yield_task) (struct rq *rq);

	bool (*yield_to_task) (struct rq *rq, struct task_struct *p, bool preempt);



	void (*check_preempt_curr) (struct rq *rq, struct task_struct *p, int flags);
@@ -1972,6 +1973,7 @@ static inline int rt_mutex_getprio(struct task_struct *p) 
# define rt_mutex_adjust_pi(p)		do { } while (0)

#endif



extern bool yield_to(struct task_struct *p, bool preempt);

extern void set_user_nice(struct task_struct *p, long nice);

extern int task_prio(const struct task_struct *p);

extern int task_nice(const struct task_struct *p);

kernel/sched.c

+85 −0
Original line number Diff line number Diff line
@@ -1686,6 +1686,39 @@ static void double_rq_unlock(struct rq *rq1, struct rq *rq2) 
		__release(rq2->lock);

}



#else /* CONFIG_SMP */



/*

 * double_rq_lock - safely lock two runqueues

 *

 * Note this does not disable interrupts like task_rq_lock,

 * you need to do so manually before calling.

 */

static void double_rq_lock(struct rq *rq1, struct rq *rq2)

	__acquires(rq1->lock)

	__acquires(rq2->lock)

{

	BUG_ON(!irqs_disabled());

	BUG_ON(rq1 != rq2);

	raw_spin_lock(&rq1->lock);

	__acquire(rq2->lock);	/* Fake it out ;) */

}



/*

 * double_rq_unlock - safely unlock two runqueues

 *

 * Note this does not restore interrupts like task_rq_unlock,

 * you need to do so manually after calling.

 */

static void double_rq_unlock(struct rq *rq1, struct rq *rq2)

	__releases(rq1->lock)

	__releases(rq2->lock)

{

	BUG_ON(rq1 != rq2);

	raw_spin_unlock(&rq1->lock);

	__release(rq2->lock);

}



#endif



static void calc_load_account_idle(struct rq *this_rq);
@@ -5448,6 +5481,58 @@ void __sched yield(void) 
}

EXPORT_SYMBOL(yield);



/**

 * yield_to - yield the current processor to another thread in

 * your thread group, or accelerate that thread toward the

 * processor it's on.

 *

 * It's the caller's job to ensure that the target task struct

 * can't go away on us before we can do any checks.

 *

 * Returns true if we indeed boosted the target task.

 */

bool __sched yield_to(struct task_struct *p, bool preempt)

{

	struct task_struct *curr = current;

	struct rq *rq, *p_rq;

	unsigned long flags;

	bool yielded = 0;



	local_irq_save(flags);

	rq = this_rq();



again:

	p_rq = task_rq(p);

	double_rq_lock(rq, p_rq);

	while (task_rq(p) != p_rq) {

		double_rq_unlock(rq, p_rq);

		goto again;

	}



	if (!curr->sched_class->yield_to_task)

		goto out;



	if (curr->sched_class != p->sched_class)

		goto out;



	if (task_running(p_rq, p) || p->state)

		goto out;



	yielded = curr->sched_class->yield_to_task(rq, p, preempt);

	if (yielded)

		schedstat_inc(rq, yld_count);



out:

	double_rq_unlock(rq, p_rq);

	local_irq_restore(flags);



	if (yielded)

		schedule();



	return yielded;

}

EXPORT_SYMBOL_GPL(yield_to);



/*

 * This task is about to go to sleep on IO. Increment rq->nr_iowait so

 * that process accounting knows that this is a task in IO wait state.

kernel/sched_fair.c

+20 −0
Original line number Diff line number Diff line
@@ -1975,6 +1975,25 @@ static void yield_task_fair(struct rq *rq) 
	set_skip_buddy(se);

}



static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preempt)

{

	struct sched_entity *se = &p->se;



	if (!se->on_rq)

		return false;



	/* Tell the scheduler that we'd really like pse to run next. */

	set_next_buddy(se);



	/* Make p's CPU reschedule; pick_next_entity takes care of fairness. */

	if (preempt)

		resched_task(rq->curr);



	yield_task_fair(rq);



	return true;

}



#ifdef CONFIG_SMP

/**************************************************

 * Fair scheduling class load-balancing methods:
@@ -4243,6 +4262,7 @@ static const struct sched_class fair_sched_class = { 
	.enqueue_task		= enqueue_task_fair,

	.dequeue_task		= dequeue_task_fair,

	.yield_task		= yield_task_fair,

	.yield_to_task		= yield_to_task_fair,



	.check_preempt_curr	= check_preempt_wakeup,

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