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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>
This commit is contained in:
Peter Zijlstra 2013-12-19 11:54:45 +01:00 committed by Ingo Molnar
parent 1724813d9f
commit de212f18e9
1 changed files with 32 additions and 51 deletions
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83
kernel/sched/core.c
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@ -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 @@ out:
}
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)