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Commit 1e5a7405 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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sched: Fix cross-sched-class wakeup preemption 



Instead of dealing with sched classes inside each check_preempt_curr()
implementation, pull out this logic into the generic wakeup preemption
path.

This fixes a hang in KVM (and others) where we are waiting for the
stop machine thread to run ...

Reported-by: default avatarMarkus Trippelsdorf <markus@trippelsdorf.de>
Tested-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Tested-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1288891946.2039.31.camel@laptop>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2d467090

kernel/sched.c

+26 −11
Original line number Original line Diff line number Diff line
@@ -560,18 +560,8 @@ struct rq { 




static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);

static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);





static inline

void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)

{

	rq->curr->sched_class->check_preempt_curr(rq, p, flags);





	/*

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

	 * A queue event has occurred, and we're going to schedule.  In

	 * this case, we can save a useless back to back clock update.

	 */

	if (test_tsk_need_resched(p))

		rq->skip_clock_update = 1;

}





static inline int cpu_of(struct rq *rq)

static inline int cpu_of(struct rq *rq)

{

{
@@ -2118,6 +2108,31 @@ static inline void check_class_changed(struct rq *rq, struct task_struct *p, 
		p->sched_class->prio_changed(rq, p, oldprio, running);

		p->sched_class->prio_changed(rq, p, oldprio, running);

}

}





static void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)

{

	const struct sched_class *class;



	if (p->sched_class == rq->curr->sched_class) {

		rq->curr->sched_class->check_preempt_curr(rq, p, flags);

	} else {

		for_each_class(class) {

			if (class == rq->curr->sched_class)

				break;

			if (class == p->sched_class) {

				resched_task(rq->curr);

				break;

			}

		}

	}



	/*

	 * A queue event has occurred, and we're going to schedule.  In

	 * this case, we can save a useless back to back clock update.

	 */

	if (test_tsk_need_resched(rq->curr))

		rq->skip_clock_update = 1;

}



#ifdef CONFIG_SMP

#ifdef CONFIG_SMP

/*

/*

 * Is this task likely cache-hot:

 * Is this task likely cache-hot:

kernel/sched_fair.c

+0 −6
Original line number Original line Diff line number Diff line
@@ -1654,12 +1654,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ 
	struct cfs_rq *cfs_rq = task_cfs_rq(curr);

	struct cfs_rq *cfs_rq = task_cfs_rq(curr);

	int scale = cfs_rq->nr_running >= sched_nr_latency;

	int scale = cfs_rq->nr_running >= sched_nr_latency;





	if (unlikely(rt_prio(p->prio)))

		goto preempt;



	if (unlikely(p->sched_class != &fair_sched_class))

		return;



	if (unlikely(se == pse))

	if (unlikely(se == pse))

		return;

		return;

kernel/sched_stoptask.c

+1 −1
Original line number Original line Diff line number Diff line
@@ -19,7 +19,7 @@ select_task_rq_stop(struct rq *rq, struct task_struct *p, 
static void

static void

check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)

check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)

{

{

	resched_task(rq->curr); /* we preempt everything */

	/* we're never preempted */

}

}





static struct task_struct *pick_next_task_stop(struct rq *rq)

static struct task_struct *pick_next_task_stop(struct rq *rq)