linux/kernel/sched_rt.c
Gregory Haskins 8ae121ac86 sched: fix RT task-wakeup logic
Dmitry Adamushko pointed out a logic error in task_wake_up_rt() where we
will always evaluate to "true".  You can find the thread here:

http://lkml.org/lkml/2008/4/22/296

In reality, we only want to try to push tasks away when a wake up request is
not going to preempt the current task.  So lets fix it.

Note: We introduce test_tsk_need_resched() instead of open-coding the flag
check so that the merge-conflict with -rt should help remind us that we
may need to support NEEDS_RESCHED_DELAYED in the future, too.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-05-05 23:56:18 +02:00

1347 lines
31 KiB
C

/*
* Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
* policies)
*/
#ifdef CONFIG_SMP
static inline int rt_overloaded(struct rq *rq)
{
return atomic_read(&rq->rd->rto_count);
}
static inline void rt_set_overload(struct rq *rq)
{
cpu_set(rq->cpu, rq->rd->rto_mask);
/*
* Make sure the mask is visible before we set
* the overload count. That is checked to determine
* if we should look at the mask. It would be a shame
* if we looked at the mask, but the mask was not
* updated yet.
*/
wmb();
atomic_inc(&rq->rd->rto_count);
}
static inline void rt_clear_overload(struct rq *rq)
{
/* the order here really doesn't matter */
atomic_dec(&rq->rd->rto_count);
cpu_clear(rq->cpu, rq->rd->rto_mask);
}
static void update_rt_migration(struct rq *rq)
{
if (rq->rt.rt_nr_migratory && (rq->rt.rt_nr_running > 1)) {
if (!rq->rt.overloaded) {
rt_set_overload(rq);
rq->rt.overloaded = 1;
}
} else if (rq->rt.overloaded) {
rt_clear_overload(rq);
rq->rt.overloaded = 0;
}
}
#endif /* CONFIG_SMP */
static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
{
return container_of(rt_se, struct task_struct, rt);
}
static inline int on_rt_rq(struct sched_rt_entity *rt_se)
{
return !list_empty(&rt_se->run_list);
}
#ifdef CONFIG_RT_GROUP_SCHED
static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
if (!rt_rq->tg)
return RUNTIME_INF;
return rt_rq->rt_runtime;
}
static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
}
#define for_each_leaf_rt_rq(rt_rq, rq) \
list_for_each_entry(rt_rq, &rq->leaf_rt_rq_list, leaf_rt_rq_list)
static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
return rt_rq->rq;
}
static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
{
return rt_se->rt_rq;
}
#define for_each_sched_rt_entity(rt_se) \
for (; rt_se; rt_se = rt_se->parent)
static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
{
return rt_se->my_q;
}
static void enqueue_rt_entity(struct sched_rt_entity *rt_se);
static void dequeue_rt_entity(struct sched_rt_entity *rt_se);
static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
struct sched_rt_entity *rt_se = rt_rq->rt_se;
if (rt_se && !on_rt_rq(rt_se) && rt_rq->rt_nr_running) {
struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
enqueue_rt_entity(rt_se);
if (rt_rq->highest_prio < curr->prio)
resched_task(curr);
}
}
static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
struct sched_rt_entity *rt_se = rt_rq->rt_se;
if (rt_se && on_rt_rq(rt_se))
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;
}
#ifdef CONFIG_SMP
static inline cpumask_t sched_rt_period_mask(void)
{
return cpu_rq(smp_processor_id())->rd->span;
}
#else
static inline cpumask_t sched_rt_period_mask(void)
{
return cpu_online_map;
}
#endif
static inline
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
{
return container_of(rt_b, struct task_group, rt_bandwidth)->rt_rq[cpu];
}
static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
return &rt_rq->tg->rt_bandwidth;
}
#else
static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
return rt_rq->rt_runtime;
}
static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
return ktime_to_ns(def_rt_bandwidth.rt_period);
}
#define for_each_leaf_rt_rq(rt_rq, rq) \
for (rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
return container_of(rt_rq, struct rq, rt);
}
static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
{
struct task_struct *p = rt_task_of(rt_se);
struct rq *rq = task_rq(p);
return &rq->rt;
}
#define for_each_sched_rt_entity(rt_se) \
for (; rt_se; rt_se = NULL)
static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
{
return NULL;
}
static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
}
static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
}
static inline int rt_rq_throttled(struct rt_rq *rt_rq)
{
return rt_rq->rt_throttled;
}
static inline cpumask_t sched_rt_period_mask(void)
{
return cpu_online_map;
}
static inline
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
{
return &cpu_rq(cpu)->rt;
}
static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
return &def_rt_bandwidth;
}
#endif
static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
{
int i, idle = 1;
cpumask_t span;
if (rt_b->rt_runtime == RUNTIME_INF)
return 1;
span = sched_rt_period_mask();
for_each_cpu_mask(i, span) {
int enqueue = 0;
struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
struct rq *rq = rq_of_rt_rq(rt_rq);
spin_lock(&rq->lock);
if (rt_rq->rt_time) {
u64 runtime;
spin_lock(&rt_rq->rt_runtime_lock);
runtime = rt_rq->rt_runtime;
rt_rq->rt_time -= min(rt_rq->rt_time, overrun*runtime);
if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
rt_rq->rt_throttled = 0;
enqueue = 1;
}
if (rt_rq->rt_time || rt_rq->rt_nr_running)
idle = 0;
spin_unlock(&rt_rq->rt_runtime_lock);
}
if (enqueue)
sched_rt_rq_enqueue(rt_rq);
spin_unlock(&rq->lock);
}
return idle;
}
#ifdef CONFIG_SMP
static int balance_runtime(struct rt_rq *rt_rq)
{
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
int i, weight, more = 0;
u64 rt_period;
weight = cpus_weight(rd->span);
spin_lock(&rt_b->rt_runtime_lock);
rt_period = ktime_to_ns(rt_b->rt_period);
for_each_cpu_mask(i, rd->span) {
struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
s64 diff;
if (iter == rt_rq)
continue;
spin_lock(&iter->rt_runtime_lock);
diff = iter->rt_runtime - iter->rt_time;
if (diff > 0) {
do_div(diff, weight);
if (rt_rq->rt_runtime + diff > rt_period)
diff = rt_period - rt_rq->rt_runtime;
iter->rt_runtime -= diff;
rt_rq->rt_runtime += diff;
more = 1;
if (rt_rq->rt_runtime == rt_period) {
spin_unlock(&iter->rt_runtime_lock);
break;
}
}
spin_unlock(&iter->rt_runtime_lock);
}
spin_unlock(&rt_b->rt_runtime_lock);
return more;
}
#endif
static inline int rt_se_prio(struct sched_rt_entity *rt_se)
{
#ifdef CONFIG_RT_GROUP_SCHED
struct rt_rq *rt_rq = group_rt_rq(rt_se);
if (rt_rq)
return rt_rq->highest_prio;
#endif
return rt_task_of(rt_se)->prio;
}
static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
{
u64 runtime = sched_rt_runtime(rt_rq);
if (runtime == RUNTIME_INF)
return 0;
if (rt_rq->rt_throttled)
return rt_rq_throttled(rt_rq);
if (sched_rt_runtime(rt_rq) >= sched_rt_period(rt_rq))
return 0;
#ifdef CONFIG_SMP
if (rt_rq->rt_time > runtime) {
int more;
spin_unlock(&rt_rq->rt_runtime_lock);
more = balance_runtime(rt_rq);
spin_lock(&rt_rq->rt_runtime_lock);
if (more)
runtime = sched_rt_runtime(rt_rq);
}
#endif
if (rt_rq->rt_time > runtime) {
rt_rq->rt_throttled = 1;
if (rt_rq_throttled(rt_rq)) {
sched_rt_rq_dequeue(rt_rq);
return 1;
}
}
return 0;
}
/*
* Update the current task's runtime statistics. Skip current tasks that
* are not in our scheduling class.
*/
static void update_curr_rt(struct rq *rq)
{
struct task_struct *curr = rq->curr;
struct sched_rt_entity *rt_se = &curr->rt;
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
u64 delta_exec;
if (!task_has_rt_policy(curr))
return;
delta_exec = rq->clock - curr->se.exec_start;
if (unlikely((s64)delta_exec < 0))
delta_exec = 0;
schedstat_set(curr->se.exec_max, max(curr->se.exec_max, delta_exec));
curr->se.sum_exec_runtime += delta_exec;
curr->se.exec_start = rq->clock;
cpuacct_charge(curr, delta_exec);
for_each_sched_rt_entity(rt_se) {
rt_rq = rt_rq_of_se(rt_se);
spin_lock(&rt_rq->rt_runtime_lock);
rt_rq->rt_time += delta_exec;
if (sched_rt_runtime_exceeded(rt_rq))
resched_task(curr);
spin_unlock(&rt_rq->rt_runtime_lock);
}
}
static inline
void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
WARN_ON(!rt_prio(rt_se_prio(rt_se)));
rt_rq->rt_nr_running++;
#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
if (rt_se_prio(rt_se) < rt_rq->highest_prio)
rt_rq->highest_prio = rt_se_prio(rt_se);
#endif
#ifdef CONFIG_SMP
if (rt_se->nr_cpus_allowed > 1) {
struct rq *rq = rq_of_rt_rq(rt_rq);
rq->rt.rt_nr_migratory++;
}
update_rt_migration(rq_of_rt_rq(rt_rq));
#endif
#ifdef CONFIG_RT_GROUP_SCHED
if (rt_se_boosted(rt_se))
rt_rq->rt_nr_boosted++;
if (rt_rq->tg)
start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
#else
start_rt_bandwidth(&def_rt_bandwidth);
#endif
}
static inline
void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
WARN_ON(!rt_prio(rt_se_prio(rt_se)));
WARN_ON(!rt_rq->rt_nr_running);
rt_rq->rt_nr_running--;
#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
if (rt_rq->rt_nr_running) {
struct rt_prio_array *array;
WARN_ON(rt_se_prio(rt_se) < rt_rq->highest_prio);
if (rt_se_prio(rt_se) == rt_rq->highest_prio) {
/* recalculate */
array = &rt_rq->active;
rt_rq->highest_prio =
sched_find_first_bit(array->bitmap);
} /* otherwise leave rq->highest prio alone */
} else
rt_rq->highest_prio = MAX_RT_PRIO;
#endif
#ifdef CONFIG_SMP
if (rt_se->nr_cpus_allowed > 1) {
struct rq *rq = rq_of_rt_rq(rt_rq);
rq->rt.rt_nr_migratory--;
}
update_rt_migration(rq_of_rt_rq(rt_rq));
#endif /* CONFIG_SMP */
#ifdef CONFIG_RT_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)
{
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
struct rt_prio_array *array = &rt_rq->active;
struct rt_rq *group_rq = group_rt_rq(rt_se);
if (group_rq && rt_rq_throttled(group_rq))
return;
list_add_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
__set_bit(rt_se_prio(rt_se), array->bitmap);
inc_rt_tasks(rt_se, rt_rq);
}
static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
{
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
struct rt_prio_array *array = &rt_rq->active;
list_del_init(&rt_se->run_list);
if (list_empty(array->queue + rt_se_prio(rt_se)))
__clear_bit(rt_se_prio(rt_se), array->bitmap);
dec_rt_tasks(rt_se, rt_rq);
}
/*
* Because the prio of an upper entry depends on the lower
* entries, we must remove entries top - down.
*/
static void dequeue_rt_stack(struct task_struct *p)
{
struct sched_rt_entity *rt_se, *back = NULL;
rt_se = &p->rt;
for_each_sched_rt_entity(rt_se) {
rt_se->back = back;
back = rt_se;
}
for (rt_se = back; rt_se; rt_se = rt_se->back) {
if (on_rt_rq(rt_se))
dequeue_rt_entity(rt_se);
}
}
/*
* Adding/removing a task to/from a priority array:
*/
static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
{
struct sched_rt_entity *rt_se = &p->rt;
if (wakeup)
rt_se->timeout = 0;
dequeue_rt_stack(p);
/*
* enqueue everybody, bottom - up.
*/
for_each_sched_rt_entity(rt_se)
enqueue_rt_entity(rt_se);
inc_cpu_load(rq, p->se.load.weight);
}
static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
{
struct sched_rt_entity *rt_se = &p->rt;
struct rt_rq *rt_rq;
update_curr_rt(rq);
dequeue_rt_stack(p);
/*
* re-enqueue all non-empty rt_rq entities.
*/
for_each_sched_rt_entity(rt_se) {
rt_rq = group_rt_rq(rt_se);
if (rt_rq && rt_rq->rt_nr_running)
enqueue_rt_entity(rt_se);
}
dec_cpu_load(rq, p->se.load.weight);
}
/*
* Put task to the end of the run list without the overhead of dequeue
* followed by enqueue.
*/
static
void requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
{
struct rt_prio_array *array = &rt_rq->active;
list_move_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
}
static void requeue_task_rt(struct rq *rq, struct task_struct *p)
{
struct sched_rt_entity *rt_se = &p->rt;
struct rt_rq *rt_rq;
for_each_sched_rt_entity(rt_se) {
rt_rq = rt_rq_of_se(rt_se);
requeue_rt_entity(rt_rq, rt_se);
}
}
static void yield_task_rt(struct rq *rq)
{
requeue_task_rt(rq, rq->curr);
}
#ifdef CONFIG_SMP
static int find_lowest_rq(struct task_struct *task);
static int select_task_rq_rt(struct task_struct *p, int sync)
{
struct rq *rq = task_rq(p);
/*
* If the current task is an RT task, then
* try to see if we can wake this RT task up on another
* runqueue. Otherwise simply start this RT task
* on its current runqueue.
*
* We want to avoid overloading runqueues. Even if
* the RT task is of higher priority than the current RT task.
* RT tasks behave differently than other tasks. If
* one gets preempted, we try to push it off to another queue.
* So trying to keep a preempting RT task on the same
* cache hot CPU will force the running RT task to
* a cold CPU. So we waste all the cache for the lower
* RT task in hopes of saving some of a RT task
* that is just being woken and probably will have
* cold cache anyway.
*/
if (unlikely(rt_task(rq->curr)) &&
(p->rt.nr_cpus_allowed > 1)) {
int cpu = find_lowest_rq(p);
return (cpu == -1) ? task_cpu(p) : cpu;
}
/*
* Otherwise, just let it ride on the affined RQ and the
* post-schedule router will push the preempted task away
*/
return task_cpu(p);
}
#endif /* CONFIG_SMP */
/*
* Preempt the current task with a newly woken task if needed:
*/
static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
{
if (p->prio < rq->curr->prio)
resched_task(rq->curr);
}
static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
struct rt_rq *rt_rq)
{
struct rt_prio_array *array = &rt_rq->active;
struct sched_rt_entity *next = NULL;
struct list_head *queue;
int idx;
idx = sched_find_first_bit(array->bitmap);
BUG_ON(idx >= MAX_RT_PRIO);
queue = array->queue + idx;
next = list_entry(queue->next, struct sched_rt_entity, run_list);
return next;
}
static struct task_struct *pick_next_task_rt(struct rq *rq)
{
struct sched_rt_entity *rt_se;
struct task_struct *p;
struct rt_rq *rt_rq;
rt_rq = &rq->rt;
if (unlikely(!rt_rq->rt_nr_running))
return NULL;
if (rt_rq_throttled(rt_rq))
return NULL;
do {
rt_se = pick_next_rt_entity(rq, rt_rq);
BUG_ON(!rt_se);
rt_rq = group_rt_rq(rt_se);
} while (rt_rq);
p = rt_task_of(rt_se);
p->se.exec_start = rq->clock;
return p;
}
static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
{
update_curr_rt(rq);
p->se.exec_start = 0;
}
#ifdef CONFIG_SMP
/* Only try algorithms three times */
#define RT_MAX_TRIES 3
static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
{
if (!task_running(rq, p) &&
(cpu < 0 || cpu_isset(cpu, p->cpus_allowed)) &&
(p->rt.nr_cpus_allowed > 1))
return 1;
return 0;
}
/* Return the second highest RT task, NULL otherwise */
static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu)
{
struct task_struct *next = NULL;
struct sched_rt_entity *rt_se;
struct rt_prio_array *array;
struct rt_rq *rt_rq;
int idx;
for_each_leaf_rt_rq(rt_rq, rq) {
array = &rt_rq->active;
idx = sched_find_first_bit(array->bitmap);
next_idx:
if (idx >= MAX_RT_PRIO)
continue;
if (next && next->prio < idx)
continue;
list_for_each_entry(rt_se, array->queue + idx, run_list) {
struct task_struct *p = rt_task_of(rt_se);
if (pick_rt_task(rq, p, cpu)) {
next = p;
break;
}
}
if (!next) {
idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
goto next_idx;
}
}
return next;
}
static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
{
int lowest_prio = -1;
int lowest_cpu = -1;
int count = 0;
int cpu;
cpus_and(*lowest_mask, task_rq(task)->rd->online, task->cpus_allowed);
/*
* Scan each rq for the lowest prio.
*/
for_each_cpu_mask(cpu, *lowest_mask) {
struct rq *rq = cpu_rq(cpu);
/* We look for lowest RT prio or non-rt CPU */
if (rq->rt.highest_prio >= MAX_RT_PRIO) {
/*
* if we already found a low RT queue
* and now we found this non-rt queue
* clear the mask and set our bit.
* Otherwise just return the queue as is
* and the count==1 will cause the algorithm
* to use the first bit found.
*/
if (lowest_cpu != -1) {
cpus_clear(*lowest_mask);
cpu_set(rq->cpu, *lowest_mask);
}
return 1;
}
/* no locking for now */
if ((rq->rt.highest_prio > task->prio)
&& (rq->rt.highest_prio >= lowest_prio)) {
if (rq->rt.highest_prio > lowest_prio) {
/* new low - clear old data */
lowest_prio = rq->rt.highest_prio;
lowest_cpu = cpu;
count = 0;
}
count++;
} else
cpu_clear(cpu, *lowest_mask);
}
/*
* Clear out all the set bits that represent
* runqueues that were of higher prio than
* the lowest_prio.
*/
if (lowest_cpu > 0) {
/*
* Perhaps we could add another cpumask op to
* zero out bits. Like cpu_zero_bits(cpumask, nrbits);
* Then that could be optimized to use memset and such.
*/
for_each_cpu_mask(cpu, *lowest_mask) {
if (cpu >= lowest_cpu)
break;
cpu_clear(cpu, *lowest_mask);
}
}
return count;
}
static inline int pick_optimal_cpu(int this_cpu, cpumask_t *mask)
{
int first;
/* "this_cpu" is cheaper to preempt than a remote processor */
if ((this_cpu != -1) && cpu_isset(this_cpu, *mask))
return this_cpu;
first = first_cpu(*mask);
if (first != NR_CPUS)
return first;
return -1;
}
static int find_lowest_rq(struct task_struct *task)
{
struct sched_domain *sd;
cpumask_t *lowest_mask = &__get_cpu_var(local_cpu_mask);
int this_cpu = smp_processor_id();
int cpu = task_cpu(task);
int count = find_lowest_cpus(task, lowest_mask);
if (!count)
return -1; /* No targets found */
/*
* There is no sense in performing an optimal search if only one
* target is found.
*/
if (count == 1)
return first_cpu(*lowest_mask);
/*
* At this point we have built a mask of cpus representing the
* lowest priority tasks in the system. Now we want to elect
* the best one based on our affinity and topology.
*
* We prioritize the last cpu that the task executed on since
* it is most likely cache-hot in that location.
*/
if (cpu_isset(cpu, *lowest_mask))
return cpu;
/*
* Otherwise, we consult the sched_domains span maps to figure
* out which cpu is logically closest to our hot cache data.
*/
if (this_cpu == cpu)
this_cpu = -1; /* Skip this_cpu opt if the same */
for_each_domain(cpu, sd) {
if (sd->flags & SD_WAKE_AFFINE) {
cpumask_t domain_mask;
int best_cpu;
cpus_and(domain_mask, sd->span, *lowest_mask);
best_cpu = pick_optimal_cpu(this_cpu,
&domain_mask);
if (best_cpu != -1)
return best_cpu;
}
}
/*
* And finally, if there were no matches within the domains
* just give the caller *something* to work with from the compatible
* locations.
*/
return pick_optimal_cpu(this_cpu, lowest_mask);
}
/* Will lock the rq it finds */
static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
{
struct rq *lowest_rq = NULL;
int tries;
int cpu;
for (tries = 0; tries < RT_MAX_TRIES; tries++) {
cpu = find_lowest_rq(task);
if ((cpu == -1) || (cpu == rq->cpu))
break;
lowest_rq = cpu_rq(cpu);
/* if the prio of this runqueue changed, try again */
if (double_lock_balance(rq, lowest_rq)) {
/*
* We had to unlock the run queue. In
* the mean time, task could have
* migrated already or had its affinity changed.
* Also make sure that it wasn't scheduled on its rq.
*/
if (unlikely(task_rq(task) != rq ||
!cpu_isset(lowest_rq->cpu,
task->cpus_allowed) ||
task_running(rq, task) ||
!task->se.on_rq)) {
spin_unlock(&lowest_rq->lock);
lowest_rq = NULL;
break;
}
}
/* If this rq is still suitable use it. */
if (lowest_rq->rt.highest_prio > task->prio)
break;
/* try again */
spin_unlock(&lowest_rq->lock);
lowest_rq = NULL;
}
return lowest_rq;
}
/*
* If the current CPU has more than one RT task, see if the non
* running task can migrate over to a CPU that is running a task
* of lesser priority.
*/
static int push_rt_task(struct rq *rq)
{
struct task_struct *next_task;
struct rq *lowest_rq;
int ret = 0;
int paranoid = RT_MAX_TRIES;
if (!rq->rt.overloaded)
return 0;
next_task = pick_next_highest_task_rt(rq, -1);
if (!next_task)
return 0;
retry:
if (unlikely(next_task == rq->curr)) {
WARN_ON(1);
return 0;
}
/*
* It's possible that the next_task slipped in of
* higher priority than current. If that's the case
* just reschedule current.
*/
if (unlikely(next_task->prio < rq->curr->prio)) {
resched_task(rq->curr);
return 0;
}
/* We might release rq lock */
get_task_struct(next_task);
/* find_lock_lowest_rq locks the rq if found */
lowest_rq = find_lock_lowest_rq(next_task, rq);
if (!lowest_rq) {
struct task_struct *task;
/*
* find lock_lowest_rq releases rq->lock
* so it is possible that next_task has changed.
* If it has, then try again.
*/
task = pick_next_highest_task_rt(rq, -1);
if (unlikely(task != next_task) && task && paranoid--) {
put_task_struct(next_task);
next_task = task;
goto retry;
}
goto out;
}
deactivate_task(rq, next_task, 0);
set_task_cpu(next_task, lowest_rq->cpu);
activate_task(lowest_rq, next_task, 0);
resched_task(lowest_rq->curr);
spin_unlock(&lowest_rq->lock);
ret = 1;
out:
put_task_struct(next_task);
return ret;
}
/*
* TODO: Currently we just use the second highest prio task on
* the queue, and stop when it can't migrate (or there's
* no more RT tasks). There may be a case where a lower
* priority RT task has a different affinity than the
* higher RT task. In this case the lower RT task could
* possibly be able to migrate where as the higher priority
* RT task could not. We currently ignore this issue.
* Enhancements are welcome!
*/
static void push_rt_tasks(struct rq *rq)
{
/* push_rt_task will return true if it moved an RT */
while (push_rt_task(rq))
;
}
static int pull_rt_task(struct rq *this_rq)
{
int this_cpu = this_rq->cpu, ret = 0, cpu;
struct task_struct *p, *next;
struct rq *src_rq;
if (likely(!rt_overloaded(this_rq)))
return 0;
next = pick_next_task_rt(this_rq);
for_each_cpu_mask(cpu, this_rq->rd->rto_mask) {
if (this_cpu == cpu)
continue;
src_rq = cpu_rq(cpu);
/*
* We can potentially drop this_rq's lock in
* double_lock_balance, and another CPU could
* steal our next task - hence we must cause
* the caller to recalculate the next task
* in that case:
*/
if (double_lock_balance(this_rq, src_rq)) {
struct task_struct *old_next = next;
next = pick_next_task_rt(this_rq);
if (next != old_next)
ret = 1;
}
/*
* Are there still pullable RT tasks?
*/
if (src_rq->rt.rt_nr_running <= 1)
goto skip;
p = pick_next_highest_task_rt(src_rq, this_cpu);
/*
* Do we have an RT task that preempts
* the to-be-scheduled task?
*/
if (p && (!next || (p->prio < next->prio))) {
WARN_ON(p == src_rq->curr);
WARN_ON(!p->se.on_rq);
/*
* There's a chance that p is higher in priority
* than what's currently running on its cpu.
* This is just that p is wakeing up and hasn't
* had a chance to schedule. We only pull
* p if it is lower in priority than the
* current task on the run queue or
* this_rq next task is lower in prio than
* the current task on that rq.
*/
if (p->prio < src_rq->curr->prio ||
(next && next->prio < src_rq->curr->prio))
goto skip;
ret = 1;
deactivate_task(src_rq, p, 0);
set_task_cpu(p, this_cpu);
activate_task(this_rq, p, 0);
/*
* We continue with the search, just in
* case there's an even higher prio task
* in another runqueue. (low likelyhood
* but possible)
*
* Update next so that we won't pick a task
* on another cpu with a priority lower (or equal)
* than the one we just picked.
*/
next = p;
}
skip:
spin_unlock(&src_rq->lock);
}
return ret;
}
static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
{
/* Try to pull RT tasks here if we lower this rq's prio */
if (unlikely(rt_task(prev)) && rq->rt.highest_prio > prev->prio)
pull_rt_task(rq);
}
static void post_schedule_rt(struct rq *rq)
{
/*
* If we have more than one rt_task queued, then
* see if we can push the other rt_tasks off to other CPUS.
* Note we may release the rq lock, and since
* the lock was owned by prev, we need to release it
* first via finish_lock_switch and then reaquire it here.
*/
if (unlikely(rq->rt.overloaded)) {
spin_lock_irq(&rq->lock);
push_rt_tasks(rq);
spin_unlock_irq(&rq->lock);
}
}
/*
* If we are not running and we are not going to reschedule soon, we should
* try to push tasks away now
*/
static void task_wake_up_rt(struct rq *rq, struct task_struct *p)
{
if (!task_running(rq, p) &&
!test_tsk_need_resched(rq->curr) &&
rq->rt.overloaded)
push_rt_tasks(rq);
}
static unsigned long
load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
unsigned long max_load_move,
struct sched_domain *sd, enum cpu_idle_type idle,
int *all_pinned, int *this_best_prio)
{
/* don't touch RT tasks */
return 0;
}
static int
move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
struct sched_domain *sd, enum cpu_idle_type idle)
{
/* don't touch RT tasks */
return 0;
}
static void set_cpus_allowed_rt(struct task_struct *p,
const cpumask_t *new_mask)
{
int weight = cpus_weight(*new_mask);
BUG_ON(!rt_task(p));
/*
* Update the migration status of the RQ if we have an RT task
* which is running AND changing its weight value.
*/
if (p->se.on_rq && (weight != p->rt.nr_cpus_allowed)) {
struct rq *rq = task_rq(p);
if ((p->rt.nr_cpus_allowed <= 1) && (weight > 1)) {
rq->rt.rt_nr_migratory++;
} else if ((p->rt.nr_cpus_allowed > 1) && (weight <= 1)) {
BUG_ON(!rq->rt.rt_nr_migratory);
rq->rt.rt_nr_migratory--;
}
update_rt_migration(rq);
}
p->cpus_allowed = *new_mask;
p->rt.nr_cpus_allowed = weight;
}
/* Assumes rq->lock is held */
static void join_domain_rt(struct rq *rq)
{
if (rq->rt.overloaded)
rt_set_overload(rq);
}
/* Assumes rq->lock is held */
static void leave_domain_rt(struct rq *rq)
{
if (rq->rt.overloaded)
rt_clear_overload(rq);
}
/*
* When switch from the rt queue, we bring ourselves to a position
* that we might want to pull RT tasks from other runqueues.
*/
static void switched_from_rt(struct rq *rq, struct task_struct *p,
int running)
{
/*
* If there are other RT tasks then we will reschedule
* and the scheduling of the other RT tasks will handle
* the balancing. But if we are the last RT task
* we may need to handle the pulling of RT tasks
* now.
*/
if (!rq->rt.rt_nr_running)
pull_rt_task(rq);
}
#endif /* CONFIG_SMP */
/*
* When switching a task to RT, we may overload the runqueue
* with RT tasks. In this case we try to push them off to
* other runqueues.
*/
static void switched_to_rt(struct rq *rq, struct task_struct *p,
int running)
{
int check_resched = 1;
/*
* If we are already running, then there's nothing
* that needs to be done. But if we are not running
* we may need to preempt the current running task.
* If that current running task is also an RT task
* then see if we can move to another run queue.
*/
if (!running) {
#ifdef CONFIG_SMP
if (rq->rt.overloaded && push_rt_task(rq) &&
/* Don't resched if we changed runqueues */
rq != task_rq(p))
check_resched = 0;
#endif /* CONFIG_SMP */
if (check_resched && p->prio < rq->curr->prio)
resched_task(rq->curr);
}
}
/*
* Priority of the task has changed. This may cause
* us to initiate a push or pull.
*/
static void prio_changed_rt(struct rq *rq, struct task_struct *p,
int oldprio, int running)
{
if (running) {
#ifdef CONFIG_SMP
/*
* If our priority decreases while running, we
* may need to pull tasks to this runqueue.
*/
if (oldprio < p->prio)
pull_rt_task(rq);
/*
* If there's a higher priority task waiting to run
* then reschedule. Note, the above pull_rt_task
* can release the rq lock and p could migrate.
* Only reschedule if p is still on the same runqueue.
*/
if (p->prio > rq->rt.highest_prio && rq->curr == p)
resched_task(p);
#else
/* For UP simply resched on drop of prio */
if (oldprio < p->prio)
resched_task(p);
#endif /* CONFIG_SMP */
} else {
/*
* This task is not running, but if it is
* greater than the current running task
* then reschedule.
*/
if (p->prio < rq->curr->prio)
resched_task(rq->curr);
}
}
static void watchdog(struct rq *rq, struct task_struct *p)
{
unsigned long soft, hard;
if (!p->signal)
return;
soft = p->signal->rlim[RLIMIT_RTTIME].rlim_cur;
hard = p->signal->rlim[RLIMIT_RTTIME].rlim_max;
if (soft != RLIM_INFINITY) {
unsigned long next;
p->rt.timeout++;
next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
if (p->rt.timeout > next)
p->it_sched_expires = p->se.sum_exec_runtime;
}
}
static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
{
update_curr_rt(rq);
watchdog(rq, p);
/*
* RR tasks need a special form of timeslice management.
* FIFO tasks have no timeslices.
*/
if (p->policy != SCHED_RR)
return;
if (--p->rt.time_slice)
return;
p->rt.time_slice = DEF_TIMESLICE;
/*
* Requeue to the end of queue if we are not the only element
* on the queue:
*/
if (p->rt.run_list.prev != p->rt.run_list.next) {
requeue_task_rt(rq, p);
set_tsk_need_resched(p);
}
}
static void set_curr_task_rt(struct rq *rq)
{
struct task_struct *p = rq->curr;
p->se.exec_start = rq->clock;
}
static const struct sched_class rt_sched_class = {
.next = &fair_sched_class,
.enqueue_task = enqueue_task_rt,
.dequeue_task = dequeue_task_rt,
.yield_task = yield_task_rt,
#ifdef CONFIG_SMP
.select_task_rq = select_task_rq_rt,
#endif /* CONFIG_SMP */
.check_preempt_curr = check_preempt_curr_rt,
.pick_next_task = pick_next_task_rt,
.put_prev_task = put_prev_task_rt,
#ifdef CONFIG_SMP
.load_balance = load_balance_rt,
.move_one_task = move_one_task_rt,
.set_cpus_allowed = set_cpus_allowed_rt,
.join_domain = join_domain_rt,
.leave_domain = leave_domain_rt,
.pre_schedule = pre_schedule_rt,
.post_schedule = post_schedule_rt,
.task_wake_up = task_wake_up_rt,
.switched_from = switched_from_rt,
#endif
.set_curr_task = set_curr_task_rt,
.task_tick = task_tick_rt,
.prio_changed = prio_changed_rt,
.switched_to = switched_to_rt,
};