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Commit de212f18 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/deadline: Fix hotplug admission control 



The current hotplug admission control is broken because:

  CPU_DYING -> migration_call() -> migrate_tasks() -> __migrate_task()

cannot fail and hard assumes it _will_ move all tasks off of the dying
cpu, failing this will break hotplug.

The much simpler solution is a DOWN_PREPARE handler that fails when
removing one CPU gets us below the total allocated bandwidth.

Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20131220171343.GL2480@laptop.programming.kicks-ass.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1724813d

kernel/sched/core.c

+32 −51
Original line number Diff line number Diff line
@@ -1887,9 +1887,15 @@ inline struct dl_bw *dl_bw_of(int i) 
	return &cpu_rq(i)->rd->dl_bw;

}



static inline int __dl_span_weight(struct rq *rq)

static inline int dl_bw_cpus(int i)

{

	return cpumask_weight(rq->rd->span);

	struct root_domain *rd = cpu_rq(i)->rd;

	int cpus = 0;



	for_each_cpu_and(i, rd->span, cpu_active_mask)

		cpus++;



	return cpus;

}

#else

inline struct dl_bw *dl_bw_of(int i)
@@ -1897,7 +1903,7 @@ inline struct dl_bw *dl_bw_of(int i) 
	return &cpu_rq(i)->dl.dl_bw;

}



static inline int __dl_span_weight(struct rq *rq)

static inline int dl_bw_cpus(int i)

{

	return 1;

}
@@ -1938,8 +1944,7 @@ static int dl_overflow(struct task_struct *p, int policy, 
	u64 period = attr->sched_period;

	u64 runtime = attr->sched_runtime;

	u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0;

	int cpus = __dl_span_weight(task_rq(p));

	int err = -1;

	int cpus, err = -1;



	if (new_bw == p->dl.dl_bw)

		return 0;
@@ -1950,6 +1955,7 @@ static int dl_overflow(struct task_struct *p, int policy, 
	 * allocated bandwidth of the container.

	 */

	raw_spin_lock(&dl_b->lock);

	cpus = dl_bw_cpus(task_cpu(p));

	if (dl_policy(policy) && !task_has_dl_policy(p) &&

	    !__dl_overflow(dl_b, cpus, 0, new_bw)) {

		__dl_add(dl_b, new_bw);
@@ -4521,42 +4527,6 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask) 
}

EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);



/*

 * When dealing with a -deadline task, we have to check if moving it to

 * a new CPU is possible or not. In fact, this is only true iff there

 * is enough bandwidth available on such CPU, otherwise we want the

 * whole migration procedure to fail over.

 */

static inline

bool set_task_cpu_dl(struct task_struct *p, unsigned int cpu)

{

	struct dl_bw *dl_b = dl_bw_of(task_cpu(p));

	struct dl_bw *cpu_b = dl_bw_of(cpu);

	int ret = 1;

	u64 bw;



	if (dl_b == cpu_b)

		return 1;



	raw_spin_lock(&dl_b->lock);

	raw_spin_lock(&cpu_b->lock);



	bw = cpu_b->bw * cpumask_weight(cpu_rq(cpu)->rd->span);

	if (dl_bandwidth_enabled() &&

	    bw < cpu_b->total_bw + p->dl.dl_bw) {

		ret = 0;

		goto unlock;

	}

	dl_b->total_bw -= p->dl.dl_bw;

	cpu_b->total_bw += p->dl.dl_bw;



unlock:

	raw_spin_unlock(&cpu_b->lock);

	raw_spin_unlock(&dl_b->lock);



	return ret;

}



/*

 * Move (not current) task off this cpu, onto dest cpu. We're doing

 * this because either it can't run here any more (set_cpus_allowed()
@@ -4588,13 +4558,6 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) 
	if (!cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p)))

		goto fail;



	/*

	 * If p is -deadline, proceed only if there is enough

	 * bandwidth available on dest_cpu

	 */

	if (unlikely(dl_task(p)) && !set_task_cpu_dl(p, dest_cpu))

		goto fail;



	/*

	 * If we're not on a rq, the next wake-up will ensure we're

	 * placed properly.
@@ -5052,13 +5015,31 @@ static int sched_cpu_active(struct notifier_block *nfb, 
static int sched_cpu_inactive(struct notifier_block *nfb,

					unsigned long action, void *hcpu)

{

	unsigned long flags;

	long cpu = (long)hcpu;



	switch (action & ~CPU_TASKS_FROZEN) {

	case CPU_DOWN_PREPARE:

		set_cpu_active((long)hcpu, false);

		set_cpu_active(cpu, false);



		/* explicitly allow suspend */

		if (!(action & CPU_TASKS_FROZEN)) {

			struct dl_bw *dl_b = dl_bw_of(cpu);

			bool overflow;

			int cpus;



			raw_spin_lock_irqsave(&dl_b->lock, flags);

			cpus = dl_bw_cpus(cpu);

			overflow = __dl_overflow(dl_b, cpus, 0, 0);

			raw_spin_unlock_irqrestore(&dl_b->lock, flags);



			if (overflow)

				return notifier_from_errno(-EBUSY);

		}

		return NOTIFY_OK;

	default:

		return NOTIFY_DONE;

	}



	return NOTIFY_DONE;

}



static int __init migration_init(void)