Commit 23b0fdfc authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: rt-group: deal with PI 



Steven mentioned the fun case where a lock holding task will be throttled.

Simple fix: allow groups that have boosted tasks to run anyway.

If a runnable task in a throttled group gets boosted the dequeue/enqueue
done by rt_mutex_setprio() is enough to unthrottle the group.

This is ofcourse not quite correct. Two possible ways forward are:
  - second prio array for boosted tasks
  - boost to a prio ceiling (this would also work for deadline scheduling)

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 4cf5d77a

kernel/sched.c

+3 −0
Original line number Diff line number Diff line
@@ -362,6 +362,8 @@ struct rt_rq { 
	u64 rt_time;



#ifdef CONFIG_FAIR_GROUP_SCHED

	unsigned long rt_nr_boosted;



	struct rq *rq;

	struct list_head leaf_rt_rq_list;

	struct task_group *tg;
@@ -7112,6 +7114,7 @@ static void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq) 
	rt_rq->rt_throttled = 0;



#ifdef CONFIG_FAIR_GROUP_SCHED

	rt_rq->rt_nr_boosted = 0;

	rt_rq->rq = rq;

#endif

}

kernel/sched_rt.c

+38 −5
Original line number Diff line number Diff line
@@ -110,6 +110,23 @@ static void sched_rt_ratio_dequeue(struct rt_rq *rt_rq) 
		dequeue_rt_entity(rt_se);

}



static inline int rt_rq_throttled(struct rt_rq *rt_rq)

{

	return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;

}



static int rt_se_boosted(struct sched_rt_entity *rt_se)

{

	struct rt_rq *rt_rq = group_rt_rq(rt_se);

	struct task_struct *p;



	if (rt_rq)

		return !!rt_rq->rt_nr_boosted;



	p = rt_task_of(rt_se);

	return p->prio != p->normal_prio;

}



#else



static inline unsigned int sched_rt_ratio(struct rt_rq *rt_rq)
@@ -149,6 +166,10 @@ static inline void sched_rt_ratio_dequeue(struct rt_rq *rt_rq) 
{

}



static inline int rt_rq_throttled(struct rt_rq *rt_rq)

{

	return rt_rq->rt_throttled;

}

#endif



static inline int rt_se_prio(struct sched_rt_entity *rt_se)
@@ -172,7 +193,7 @@ static int sched_rt_ratio_exceeded(struct rt_rq *rt_rq) 
		return 0;



	if (rt_rq->rt_throttled)

		return 1;

		return rt_rq_throttled(rt_rq);



	period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;

	ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
@@ -183,9 +204,11 @@ static int sched_rt_ratio_exceeded(struct rt_rq *rt_rq) 
		rq->rt_throttled = 1;

		rt_rq->rt_throttled = 1;



		if (rt_rq_throttled(rt_rq)) {

			sched_rt_ratio_dequeue(rt_rq);

			return 1;

		}

	}



	return 0;

}
@@ -265,6 +288,10 @@ void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) 


	update_rt_migration(rq_of_rt_rq(rt_rq));

#endif

#ifdef CONFIG_FAIR_GROUP_SCHED

	if (rt_se_boosted(rt_se))

		rt_rq->rt_nr_boosted++;

#endif

}



static inline
@@ -295,6 +322,12 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) 


	update_rt_migration(rq_of_rt_rq(rt_rq));

#endif /* CONFIG_SMP */

#ifdef CONFIG_FAIR_GROUP_SCHED

	if (rt_se_boosted(rt_se))

		rt_rq->rt_nr_boosted--;



	WARN_ON(!rt_rq->rt_nr_running && rt_rq->rt_nr_boosted);

#endif

}



static void enqueue_rt_entity(struct sched_rt_entity *rt_se)
@@ -303,7 +336,7 @@ static void enqueue_rt_entity(struct sched_rt_entity *rt_se) 
	struct rt_prio_array *array = &rt_rq->active;

	struct rt_rq *group_rq = group_rt_rq(rt_se);



	if (group_rq && group_rq->rt_throttled)

	if (group_rq && rt_rq_throttled(group_rq))

		return;



	list_add_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
@@ -496,7 +529,7 @@ static struct task_struct *pick_next_task_rt(struct rq *rq) 
	if (unlikely(!rt_rq->rt_nr_running))

		return NULL;



	if (sched_rt_ratio_exceeded(rt_rq))

	if (rt_rq_throttled(rt_rq))

		return NULL;



	do {

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