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: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20131220171343.GL2480@laptop.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -1887,9 +1887,15 @@ inline struct dl_bw *dl_bw_of(int i)
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return &cpu_rq(i)->rd->dl_bw;
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}
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static inline int __dl_span_weight(struct rq *rq)
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static inline int dl_bw_cpus(int i)
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{
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return cpumask_weight(rq->rd->span);
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struct root_domain *rd = cpu_rq(i)->rd;
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int cpus = 0;
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for_each_cpu_and(i, rd->span, cpu_active_mask)
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cpus++;
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return cpus;
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}
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#else
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inline struct dl_bw *dl_bw_of(int i)
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@ -1897,7 +1903,7 @@ inline struct dl_bw *dl_bw_of(int i)
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return &cpu_rq(i)->dl.dl_bw;
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}
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static inline int __dl_span_weight(struct rq *rq)
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static inline int dl_bw_cpus(int i)
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{
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return 1;
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}
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@ -1938,8 +1944,7 @@ static int dl_overflow(struct task_struct *p, int policy,
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u64 period = attr->sched_period;
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u64 runtime = attr->sched_runtime;
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u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0;
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int cpus = __dl_span_weight(task_rq(p));
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int err = -1;
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int cpus, err = -1;
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if (new_bw == p->dl.dl_bw)
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return 0;
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@ -1950,6 +1955,7 @@ static int dl_overflow(struct task_struct *p, int policy,
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* allocated bandwidth of the container.
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*/
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raw_spin_lock(&dl_b->lock);
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cpus = dl_bw_cpus(task_cpu(p));
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if (dl_policy(policy) && !task_has_dl_policy(p) &&
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!__dl_overflow(dl_b, cpus, 0, new_bw)) {
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__dl_add(dl_b, new_bw);
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@ -4521,42 +4527,6 @@ out:
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}
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EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
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/*
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* When dealing with a -deadline task, we have to check if moving it to
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* a new CPU is possible or not. In fact, this is only true iff there
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* is enough bandwidth available on such CPU, otherwise we want the
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* whole migration procedure to fail over.
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*/
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static inline
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bool set_task_cpu_dl(struct task_struct *p, unsigned int cpu)
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{
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struct dl_bw *dl_b = dl_bw_of(task_cpu(p));
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struct dl_bw *cpu_b = dl_bw_of(cpu);
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int ret = 1;
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u64 bw;
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if (dl_b == cpu_b)
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return 1;
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raw_spin_lock(&dl_b->lock);
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raw_spin_lock(&cpu_b->lock);
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bw = cpu_b->bw * cpumask_weight(cpu_rq(cpu)->rd->span);
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if (dl_bandwidth_enabled() &&
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bw < cpu_b->total_bw + p->dl.dl_bw) {
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ret = 0;
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goto unlock;
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}
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dl_b->total_bw -= p->dl.dl_bw;
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cpu_b->total_bw += p->dl.dl_bw;
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unlock:
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raw_spin_unlock(&cpu_b->lock);
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raw_spin_unlock(&dl_b->lock);
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return ret;
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}
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/*
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* Move (not current) task off this cpu, onto dest cpu. We're doing
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* this because either it can't run here any more (set_cpus_allowed()
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@ -4588,13 +4558,6 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
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if (!cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p)))
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goto fail;
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/*
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* If p is -deadline, proceed only if there is enough
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* bandwidth available on dest_cpu
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*/
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if (unlikely(dl_task(p)) && !set_task_cpu_dl(p, dest_cpu))
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goto fail;
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/*
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* If we're not on a rq, the next wake-up will ensure we're
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* placed properly.
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@ -5052,13 +5015,31 @@ static int sched_cpu_active(struct notifier_block *nfb,
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static int sched_cpu_inactive(struct notifier_block *nfb,
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unsigned long action, void *hcpu)
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{
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unsigned long flags;
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long cpu = (long)hcpu;
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switch (action & ~CPU_TASKS_FROZEN) {
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case CPU_DOWN_PREPARE:
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set_cpu_active((long)hcpu, false);
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set_cpu_active(cpu, false);
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/* explicitly allow suspend */
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if (!(action & CPU_TASKS_FROZEN)) {
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struct dl_bw *dl_b = dl_bw_of(cpu);
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bool overflow;
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int cpus;
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raw_spin_lock_irqsave(&dl_b->lock, flags);
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cpus = dl_bw_cpus(cpu);
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overflow = __dl_overflow(dl_b, cpus, 0, 0);
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raw_spin_unlock_irqrestore(&dl_b->lock, flags);
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if (overflow)
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return notifier_from_errno(-EBUSY);
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}
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return NOTIFY_OK;
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default:
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return NOTIFY_DONE;
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}
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return NOTIFY_DONE;
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}
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static int __init migration_init(void)
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