2 * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
7 static cpumask_t rt_overload_mask;
8 static atomic_t rto_count;
9 static inline int rt_overloaded(void)
11 return atomic_read(&rto_count);
13 static inline cpumask_t *rt_overload(void)
15 return &rt_overload_mask;
17 static inline void rt_set_overload(struct rq *rq)
19 cpu_set(rq->cpu, rt_overload_mask);
21 * Make sure the mask is visible before we set
22 * the overload count. That is checked to determine
23 * if we should look at the mask. It would be a shame
24 * if we looked at the mask, but the mask was not
28 atomic_inc(&rto_count);
30 static inline void rt_clear_overload(struct rq *rq)
32 /* the order here really doesn't matter */
33 atomic_dec(&rto_count);
34 cpu_clear(rq->cpu, rt_overload_mask);
37 static void update_rt_migration(struct rq *rq)
39 if (rq->rt.rt_nr_migratory && (rq->rt.rt_nr_running > 1))
42 rt_clear_overload(rq);
44 #endif /* CONFIG_SMP */
47 * Update the current task's runtime statistics. Skip current tasks that
48 * are not in our scheduling class.
50 static void update_curr_rt(struct rq *rq)
52 struct task_struct *curr = rq->curr;
55 if (!task_has_rt_policy(curr))
58 delta_exec = rq->clock - curr->se.exec_start;
59 if (unlikely((s64)delta_exec < 0))
62 schedstat_set(curr->se.exec_max, max(curr->se.exec_max, delta_exec));
64 curr->se.sum_exec_runtime += delta_exec;
65 curr->se.exec_start = rq->clock;
66 cpuacct_charge(curr, delta_exec);
69 static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
72 rq->rt.rt_nr_running++;
74 if (p->prio < rq->rt.highest_prio)
75 rq->rt.highest_prio = p->prio;
76 if (p->nr_cpus_allowed > 1)
77 rq->rt.rt_nr_migratory++;
79 update_rt_migration(rq);
80 #endif /* CONFIG_SMP */
83 static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
86 WARN_ON(!rq->rt.rt_nr_running);
87 rq->rt.rt_nr_running--;
89 if (rq->rt.rt_nr_running) {
90 struct rt_prio_array *array;
92 WARN_ON(p->prio < rq->rt.highest_prio);
93 if (p->prio == rq->rt.highest_prio) {
95 array = &rq->rt.active;
97 sched_find_first_bit(array->bitmap);
98 } /* otherwise leave rq->highest prio alone */
100 rq->rt.highest_prio = MAX_RT_PRIO;
101 if (p->nr_cpus_allowed > 1)
102 rq->rt.rt_nr_migratory--;
104 update_rt_migration(rq);
105 #endif /* CONFIG_SMP */
108 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
110 struct rt_prio_array *array = &rq->rt.active;
112 list_add_tail(&p->run_list, array->queue + p->prio);
113 __set_bit(p->prio, array->bitmap);
114 inc_cpu_load(rq, p->se.load.weight);
120 * Adding/removing a task to/from a priority array:
122 static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
124 struct rt_prio_array *array = &rq->rt.active;
128 list_del(&p->run_list);
129 if (list_empty(array->queue + p->prio))
130 __clear_bit(p->prio, array->bitmap);
131 dec_cpu_load(rq, p->se.load.weight);
137 * Put task to the end of the run list without the overhead of dequeue
138 * followed by enqueue.
140 static void requeue_task_rt(struct rq *rq, struct task_struct *p)
142 struct rt_prio_array *array = &rq->rt.active;
144 list_move_tail(&p->run_list, array->queue + p->prio);
148 yield_task_rt(struct rq *rq)
150 requeue_task_rt(rq, rq->curr);
154 static int find_lowest_rq(struct task_struct *task);
156 static int select_task_rq_rt(struct task_struct *p, int sync)
158 struct rq *rq = task_rq(p);
161 * If the task will not preempt the RQ, try to find a better RQ
162 * before we even activate the task
164 if ((p->prio >= rq->rt.highest_prio)
165 && (p->nr_cpus_allowed > 1)) {
166 int cpu = find_lowest_rq(p);
168 return (cpu == -1) ? task_cpu(p) : cpu;
172 * Otherwise, just let it ride on the affined RQ and the
173 * post-schedule router will push the preempted task away
177 #endif /* CONFIG_SMP */
180 * Preempt the current task with a newly woken task if needed:
182 static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
184 if (p->prio < rq->curr->prio)
185 resched_task(rq->curr);
188 static struct task_struct *pick_next_task_rt(struct rq *rq)
190 struct rt_prio_array *array = &rq->rt.active;
191 struct task_struct *next;
192 struct list_head *queue;
195 idx = sched_find_first_bit(array->bitmap);
196 if (idx >= MAX_RT_PRIO)
199 queue = array->queue + idx;
200 next = list_entry(queue->next, struct task_struct, run_list);
202 next->se.exec_start = rq->clock;
207 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
210 p->se.exec_start = 0;
214 /* Only try algorithms three times */
215 #define RT_MAX_TRIES 3
217 static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
218 static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
220 static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
222 if (!task_running(rq, p) &&
223 (cpu < 0 || cpu_isset(cpu, p->cpus_allowed)) &&
224 (p->nr_cpus_allowed > 1))
229 /* Return the second highest RT task, NULL otherwise */
230 static struct task_struct *pick_next_highest_task_rt(struct rq *rq,
233 struct rt_prio_array *array = &rq->rt.active;
234 struct task_struct *next;
235 struct list_head *queue;
238 assert_spin_locked(&rq->lock);
240 if (likely(rq->rt.rt_nr_running < 2))
243 idx = sched_find_first_bit(array->bitmap);
244 if (unlikely(idx >= MAX_RT_PRIO)) {
245 WARN_ON(1); /* rt_nr_running is bad */
249 queue = array->queue + idx;
250 BUG_ON(list_empty(queue));
252 next = list_entry(queue->next, struct task_struct, run_list);
253 if (unlikely(pick_rt_task(rq, next, cpu)))
256 if (queue->next->next != queue) {
258 next = list_entry(queue->next->next, struct task_struct, run_list);
259 if (pick_rt_task(rq, next, cpu))
264 /* slower, but more flexible */
265 idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
266 if (unlikely(idx >= MAX_RT_PRIO))
269 queue = array->queue + idx;
270 BUG_ON(list_empty(queue));
272 list_for_each_entry(next, queue, run_list) {
273 if (pick_rt_task(rq, next, cpu))
283 static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
285 static int find_lowest_rq(struct task_struct *task)
288 cpumask_t *cpu_mask = &__get_cpu_var(local_cpu_mask);
289 struct rq *lowest_rq = NULL;
291 cpus_and(*cpu_mask, cpu_online_map, task->cpus_allowed);
294 * Scan each rq for the lowest prio.
296 for_each_cpu_mask(cpu, *cpu_mask) {
297 struct rq *rq = cpu_rq(cpu);
299 /* We look for lowest RT prio or non-rt CPU */
300 if (rq->rt.highest_prio >= MAX_RT_PRIO) {
305 /* no locking for now */
306 if (rq->rt.highest_prio > task->prio &&
307 (!lowest_rq || rq->rt.highest_prio > lowest_rq->rt.highest_prio)) {
312 return lowest_rq ? lowest_rq->cpu : -1;
315 /* Will lock the rq it finds */
316 static struct rq *find_lock_lowest_rq(struct task_struct *task,
319 struct rq *lowest_rq = NULL;
323 for (tries = 0; tries < RT_MAX_TRIES; tries++) {
324 cpu = find_lowest_rq(task);
326 if ((cpu == -1) || (cpu == rq->cpu))
329 lowest_rq = cpu_rq(cpu);
331 /* if the prio of this runqueue changed, try again */
332 if (double_lock_balance(rq, lowest_rq)) {
334 * We had to unlock the run queue. In
335 * the mean time, task could have
336 * migrated already or had its affinity changed.
337 * Also make sure that it wasn't scheduled on its rq.
339 if (unlikely(task_rq(task) != rq ||
340 !cpu_isset(lowest_rq->cpu, task->cpus_allowed) ||
341 task_running(rq, task) ||
343 spin_unlock(&lowest_rq->lock);
349 /* If this rq is still suitable use it. */
350 if (lowest_rq->rt.highest_prio > task->prio)
354 spin_unlock(&lowest_rq->lock);
362 * If the current CPU has more than one RT task, see if the non
363 * running task can migrate over to a CPU that is running a task
364 * of lesser priority.
366 static int push_rt_task(struct rq *rq)
368 struct task_struct *next_task;
369 struct rq *lowest_rq;
371 int paranoid = RT_MAX_TRIES;
373 assert_spin_locked(&rq->lock);
375 next_task = pick_next_highest_task_rt(rq, -1);
380 if (unlikely(next_task == rq->curr)) {
386 * It's possible that the next_task slipped in of
387 * higher priority than current. If that's the case
388 * just reschedule current.
390 if (unlikely(next_task->prio < rq->curr->prio)) {
391 resched_task(rq->curr);
395 /* We might release rq lock */
396 get_task_struct(next_task);
398 /* find_lock_lowest_rq locks the rq if found */
399 lowest_rq = find_lock_lowest_rq(next_task, rq);
401 struct task_struct *task;
403 * find lock_lowest_rq releases rq->lock
404 * so it is possible that next_task has changed.
405 * If it has, then try again.
407 task = pick_next_highest_task_rt(rq, -1);
408 if (unlikely(task != next_task) && task && paranoid--) {
409 put_task_struct(next_task);
416 assert_spin_locked(&lowest_rq->lock);
418 deactivate_task(rq, next_task, 0);
419 set_task_cpu(next_task, lowest_rq->cpu);
420 activate_task(lowest_rq, next_task, 0);
422 resched_task(lowest_rq->curr);
424 spin_unlock(&lowest_rq->lock);
428 put_task_struct(next_task);
434 * TODO: Currently we just use the second highest prio task on
435 * the queue, and stop when it can't migrate (or there's
436 * no more RT tasks). There may be a case where a lower
437 * priority RT task has a different affinity than the
438 * higher RT task. In this case the lower RT task could
439 * possibly be able to migrate where as the higher priority
440 * RT task could not. We currently ignore this issue.
441 * Enhancements are welcome!
443 static void push_rt_tasks(struct rq *rq)
445 /* push_rt_task will return true if it moved an RT */
446 while (push_rt_task(rq))
450 static int pull_rt_task(struct rq *this_rq)
452 struct task_struct *next;
453 struct task_struct *p;
455 cpumask_t *rto_cpumask;
456 int this_cpu = this_rq->cpu;
460 assert_spin_locked(&this_rq->lock);
463 * If cpusets are used, and we have overlapping
464 * run queue cpusets, then this algorithm may not catch all.
465 * This is just the price you pay on trying to keep
466 * dirtying caches down on large SMP machines.
468 if (likely(!rt_overloaded()))
471 next = pick_next_task_rt(this_rq);
473 rto_cpumask = rt_overload();
475 for_each_cpu_mask(cpu, *rto_cpumask) {
479 src_rq = cpu_rq(cpu);
480 if (unlikely(src_rq->rt.rt_nr_running <= 1)) {
482 * It is possible that overlapping cpusets
483 * will miss clearing a non overloaded runqueue.
486 if (double_lock_balance(this_rq, src_rq)) {
487 /* unlocked our runqueue lock */
488 struct task_struct *old_next = next;
489 next = pick_next_task_rt(this_rq);
490 if (next != old_next)
493 if (likely(src_rq->rt.rt_nr_running <= 1))
495 * Small chance that this_rq->curr changed
496 * but it's really harmless here.
498 rt_clear_overload(this_rq);
501 * Heh, the src_rq is now overloaded, since
502 * we already have the src_rq lock, go straight
503 * to pulling tasks from it.
506 spin_unlock(&src_rq->lock);
511 * We can potentially drop this_rq's lock in
512 * double_lock_balance, and another CPU could
513 * steal our next task - hence we must cause
514 * the caller to recalculate the next task
517 if (double_lock_balance(this_rq, src_rq)) {
518 struct task_struct *old_next = next;
519 next = pick_next_task_rt(this_rq);
520 if (next != old_next)
525 * Are there still pullable RT tasks?
527 if (src_rq->rt.rt_nr_running <= 1) {
528 spin_unlock(&src_rq->lock);
533 p = pick_next_highest_task_rt(src_rq, this_cpu);
536 * Do we have an RT task that preempts
537 * the to-be-scheduled task?
539 if (p && (!next || (p->prio < next->prio))) {
540 WARN_ON(p == src_rq->curr);
541 WARN_ON(!p->se.on_rq);
544 * There's a chance that p is higher in priority
545 * than what's currently running on its cpu.
546 * This is just that p is wakeing up and hasn't
547 * had a chance to schedule. We only pull
548 * p if it is lower in priority than the
549 * current task on the run queue or
550 * this_rq next task is lower in prio than
551 * the current task on that rq.
553 if (p->prio < src_rq->curr->prio ||
554 (next && next->prio < src_rq->curr->prio))
559 deactivate_task(src_rq, p, 0);
560 set_task_cpu(p, this_cpu);
561 activate_task(this_rq, p, 0);
563 * We continue with the search, just in
564 * case there's an even higher prio task
565 * in another runqueue. (low likelyhood
570 * Update next so that we won't pick a task
571 * on another cpu with a priority lower (or equal)
572 * than the one we just picked.
578 spin_unlock(&src_rq->lock);
584 static void schedule_balance_rt(struct rq *rq,
585 struct task_struct *prev)
587 /* Try to pull RT tasks here if we lower this rq's prio */
588 if (unlikely(rt_task(prev)) &&
589 rq->rt.highest_prio > prev->prio)
593 static void schedule_tail_balance_rt(struct rq *rq)
596 * If we have more than one rt_task queued, then
597 * see if we can push the other rt_tasks off to other CPUS.
598 * Note we may release the rq lock, and since
599 * the lock was owned by prev, we need to release it
600 * first via finish_lock_switch and then reaquire it here.
602 if (unlikely(rq->rt.rt_nr_running > 1)) {
603 spin_lock_irq(&rq->lock);
605 spin_unlock_irq(&rq->lock);
610 static void wakeup_balance_rt(struct rq *rq, struct task_struct *p)
612 if (unlikely(rt_task(p)) &&
613 !task_running(rq, p) &&
614 (p->prio >= rq->curr->prio))
619 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
620 unsigned long max_load_move,
621 struct sched_domain *sd, enum cpu_idle_type idle,
622 int *all_pinned, int *this_best_prio)
624 /* don't touch RT tasks */
629 move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
630 struct sched_domain *sd, enum cpu_idle_type idle)
632 /* don't touch RT tasks */
635 static void set_cpus_allowed_rt(struct task_struct *p, cpumask_t *new_mask)
637 int weight = cpus_weight(*new_mask);
642 * Update the migration status of the RQ if we have an RT task
643 * which is running AND changing its weight value.
645 if (p->se.on_rq && (weight != p->nr_cpus_allowed)) {
646 struct rq *rq = task_rq(p);
648 if ((p->nr_cpus_allowed <= 1) && (weight > 1))
649 rq->rt.rt_nr_migratory++;
650 else if((p->nr_cpus_allowed > 1) && (weight <= 1)) {
651 BUG_ON(!rq->rt.rt_nr_migratory);
652 rq->rt.rt_nr_migratory--;
655 update_rt_migration(rq);
658 p->cpus_allowed = *new_mask;
659 p->nr_cpus_allowed = weight;
661 #else /* CONFIG_SMP */
662 # define schedule_tail_balance_rt(rq) do { } while (0)
663 # define schedule_balance_rt(rq, prev) do { } while (0)
664 # define wakeup_balance_rt(rq, p) do { } while (0)
665 #endif /* CONFIG_SMP */
667 static void task_tick_rt(struct rq *rq, struct task_struct *p)
672 * RR tasks need a special form of timeslice management.
673 * FIFO tasks have no timeslices.
675 if (p->policy != SCHED_RR)
681 p->time_slice = DEF_TIMESLICE;
684 * Requeue to the end of queue if we are not the only element
687 if (p->run_list.prev != p->run_list.next) {
688 requeue_task_rt(rq, p);
689 set_tsk_need_resched(p);
693 static void set_curr_task_rt(struct rq *rq)
695 struct task_struct *p = rq->curr;
697 p->se.exec_start = rq->clock;
700 const struct sched_class rt_sched_class = {
701 .next = &fair_sched_class,
702 .enqueue_task = enqueue_task_rt,
703 .dequeue_task = dequeue_task_rt,
704 .yield_task = yield_task_rt,
706 .select_task_rq = select_task_rq_rt,
707 #endif /* CONFIG_SMP */
709 .check_preempt_curr = check_preempt_curr_rt,
711 .pick_next_task = pick_next_task_rt,
712 .put_prev_task = put_prev_task_rt,
715 .load_balance = load_balance_rt,
716 .move_one_task = move_one_task_rt,
717 .set_cpus_allowed = set_cpus_allowed_rt,
720 .set_curr_task = set_curr_task_rt,
721 .task_tick = task_tick_rt,