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 select_task_rq_rt(struct task_struct *p, int sync)
158 #endif /* CONFIG_SMP */
161 * Preempt the current task with a newly woken task if needed:
163 static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
165 if (p->prio < rq->curr->prio)
166 resched_task(rq->curr);
169 static struct task_struct *pick_next_task_rt(struct rq *rq)
171 struct rt_prio_array *array = &rq->rt.active;
172 struct task_struct *next;
173 struct list_head *queue;
176 idx = sched_find_first_bit(array->bitmap);
177 if (idx >= MAX_RT_PRIO)
180 queue = array->queue + idx;
181 next = list_entry(queue->next, struct task_struct, run_list);
183 next->se.exec_start = rq->clock;
188 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
191 p->se.exec_start = 0;
195 /* Only try algorithms three times */
196 #define RT_MAX_TRIES 3
198 static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
199 static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
201 static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
203 if (!task_running(rq, p) &&
204 (cpu < 0 || cpu_isset(cpu, p->cpus_allowed)) &&
205 (p->nr_cpus_allowed > 1))
210 /* Return the second highest RT task, NULL otherwise */
211 static struct task_struct *pick_next_highest_task_rt(struct rq *rq,
214 struct rt_prio_array *array = &rq->rt.active;
215 struct task_struct *next;
216 struct list_head *queue;
219 assert_spin_locked(&rq->lock);
221 if (likely(rq->rt.rt_nr_running < 2))
224 idx = sched_find_first_bit(array->bitmap);
225 if (unlikely(idx >= MAX_RT_PRIO)) {
226 WARN_ON(1); /* rt_nr_running is bad */
230 queue = array->queue + idx;
231 BUG_ON(list_empty(queue));
233 next = list_entry(queue->next, struct task_struct, run_list);
234 if (unlikely(pick_rt_task(rq, next, cpu)))
237 if (queue->next->next != queue) {
239 next = list_entry(queue->next->next, struct task_struct, run_list);
240 if (pick_rt_task(rq, next, cpu))
245 /* slower, but more flexible */
246 idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
247 if (unlikely(idx >= MAX_RT_PRIO))
250 queue = array->queue + idx;
251 BUG_ON(list_empty(queue));
253 list_for_each_entry(next, queue, run_list) {
254 if (pick_rt_task(rq, next, cpu))
264 static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
266 /* Will lock the rq it finds */
267 static struct rq *find_lock_lowest_rq(struct task_struct *task,
270 struct rq *lowest_rq = NULL;
273 cpumask_t *cpu_mask = &__get_cpu_var(local_cpu_mask);
275 cpus_and(*cpu_mask, cpu_online_map, task->cpus_allowed);
277 for (tries = 0; tries < RT_MAX_TRIES; tries++) {
279 * Scan each rq for the lowest prio.
281 for_each_cpu_mask(cpu, *cpu_mask) {
282 struct rq *rq = &per_cpu(runqueues, cpu);
284 if (cpu == this_rq->cpu)
287 /* We look for lowest RT prio or non-rt CPU */
288 if (rq->rt.highest_prio >= MAX_RT_PRIO) {
293 /* no locking for now */
294 if (rq->rt.highest_prio > task->prio &&
295 (!lowest_rq || rq->rt.highest_prio > lowest_rq->rt.highest_prio)) {
303 /* if the prio of this runqueue changed, try again */
304 if (double_lock_balance(this_rq, lowest_rq)) {
306 * We had to unlock the run queue. In
307 * the mean time, task could have
308 * migrated already or had its affinity changed.
309 * Also make sure that it wasn't scheduled on its rq.
311 if (unlikely(task_rq(task) != this_rq ||
312 !cpu_isset(lowest_rq->cpu, task->cpus_allowed) ||
313 task_running(this_rq, task) ||
315 spin_unlock(&lowest_rq->lock);
321 /* If this rq is still suitable use it. */
322 if (lowest_rq->rt.highest_prio > task->prio)
326 spin_unlock(&lowest_rq->lock);
334 * If the current CPU has more than one RT task, see if the non
335 * running task can migrate over to a CPU that is running a task
336 * of lesser priority.
338 static int push_rt_task(struct rq *rq)
340 struct task_struct *next_task;
341 struct rq *lowest_rq;
343 int paranoid = RT_MAX_TRIES;
345 assert_spin_locked(&rq->lock);
347 next_task = pick_next_highest_task_rt(rq, -1);
352 if (unlikely(next_task == rq->curr)) {
358 * It's possible that the next_task slipped in of
359 * higher priority than current. If that's the case
360 * just reschedule current.
362 if (unlikely(next_task->prio < rq->curr->prio)) {
363 resched_task(rq->curr);
367 /* We might release rq lock */
368 get_task_struct(next_task);
370 /* find_lock_lowest_rq locks the rq if found */
371 lowest_rq = find_lock_lowest_rq(next_task, rq);
373 struct task_struct *task;
375 * find lock_lowest_rq releases rq->lock
376 * so it is possible that next_task has changed.
377 * If it has, then try again.
379 task = pick_next_highest_task_rt(rq, -1);
380 if (unlikely(task != next_task) && task && paranoid--) {
381 put_task_struct(next_task);
388 assert_spin_locked(&lowest_rq->lock);
390 deactivate_task(rq, next_task, 0);
391 set_task_cpu(next_task, lowest_rq->cpu);
392 activate_task(lowest_rq, next_task, 0);
394 resched_task(lowest_rq->curr);
396 spin_unlock(&lowest_rq->lock);
400 put_task_struct(next_task);
406 * TODO: Currently we just use the second highest prio task on
407 * the queue, and stop when it can't migrate (or there's
408 * no more RT tasks). There may be a case where a lower
409 * priority RT task has a different affinity than the
410 * higher RT task. In this case the lower RT task could
411 * possibly be able to migrate where as the higher priority
412 * RT task could not. We currently ignore this issue.
413 * Enhancements are welcome!
415 static void push_rt_tasks(struct rq *rq)
417 /* push_rt_task will return true if it moved an RT */
418 while (push_rt_task(rq))
422 static int pull_rt_task(struct rq *this_rq)
424 struct task_struct *next;
425 struct task_struct *p;
427 cpumask_t *rto_cpumask;
428 int this_cpu = this_rq->cpu;
432 assert_spin_locked(&this_rq->lock);
435 * If cpusets are used, and we have overlapping
436 * run queue cpusets, then this algorithm may not catch all.
437 * This is just the price you pay on trying to keep
438 * dirtying caches down on large SMP machines.
440 if (likely(!rt_overloaded()))
443 next = pick_next_task_rt(this_rq);
445 rto_cpumask = rt_overload();
447 for_each_cpu_mask(cpu, *rto_cpumask) {
451 src_rq = cpu_rq(cpu);
452 if (unlikely(src_rq->rt.rt_nr_running <= 1)) {
454 * It is possible that overlapping cpusets
455 * will miss clearing a non overloaded runqueue.
458 if (double_lock_balance(this_rq, src_rq)) {
459 /* unlocked our runqueue lock */
460 struct task_struct *old_next = next;
461 next = pick_next_task_rt(this_rq);
462 if (next != old_next)
465 if (likely(src_rq->rt.rt_nr_running <= 1))
467 * Small chance that this_rq->curr changed
468 * but it's really harmless here.
470 rt_clear_overload(this_rq);
473 * Heh, the src_rq is now overloaded, since
474 * we already have the src_rq lock, go straight
475 * to pulling tasks from it.
478 spin_unlock(&src_rq->lock);
483 * We can potentially drop this_rq's lock in
484 * double_lock_balance, and another CPU could
485 * steal our next task - hence we must cause
486 * the caller to recalculate the next task
489 if (double_lock_balance(this_rq, src_rq)) {
490 struct task_struct *old_next = next;
491 next = pick_next_task_rt(this_rq);
492 if (next != old_next)
497 * Are there still pullable RT tasks?
499 if (src_rq->rt.rt_nr_running <= 1) {
500 spin_unlock(&src_rq->lock);
505 p = pick_next_highest_task_rt(src_rq, this_cpu);
508 * Do we have an RT task that preempts
509 * the to-be-scheduled task?
511 if (p && (!next || (p->prio < next->prio))) {
512 WARN_ON(p == src_rq->curr);
513 WARN_ON(!p->se.on_rq);
516 * There's a chance that p is higher in priority
517 * than what's currently running on its cpu.
518 * This is just that p is wakeing up and hasn't
519 * had a chance to schedule. We only pull
520 * p if it is lower in priority than the
521 * current task on the run queue or
522 * this_rq next task is lower in prio than
523 * the current task on that rq.
525 if (p->prio < src_rq->curr->prio ||
526 (next && next->prio < src_rq->curr->prio))
531 deactivate_task(src_rq, p, 0);
532 set_task_cpu(p, this_cpu);
533 activate_task(this_rq, p, 0);
535 * We continue with the search, just in
536 * case there's an even higher prio task
537 * in another runqueue. (low likelyhood
542 * Update next so that we won't pick a task
543 * on another cpu with a priority lower (or equal)
544 * than the one we just picked.
550 spin_unlock(&src_rq->lock);
556 static void schedule_balance_rt(struct rq *rq,
557 struct task_struct *prev)
559 /* Try to pull RT tasks here if we lower this rq's prio */
560 if (unlikely(rt_task(prev)) &&
561 rq->rt.highest_prio > prev->prio)
565 static void schedule_tail_balance_rt(struct rq *rq)
568 * If we have more than one rt_task queued, then
569 * see if we can push the other rt_tasks off to other CPUS.
570 * Note we may release the rq lock, and since
571 * the lock was owned by prev, we need to release it
572 * first via finish_lock_switch and then reaquire it here.
574 if (unlikely(rq->rt.rt_nr_running > 1)) {
575 spin_lock_irq(&rq->lock);
577 spin_unlock_irq(&rq->lock);
582 static void wakeup_balance_rt(struct rq *rq, struct task_struct *p)
584 if (unlikely(rt_task(p)) &&
585 !task_running(rq, p) &&
586 (p->prio >= rq->curr->prio))
591 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
592 unsigned long max_load_move,
593 struct sched_domain *sd, enum cpu_idle_type idle,
594 int *all_pinned, int *this_best_prio)
596 /* don't touch RT tasks */
601 move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
602 struct sched_domain *sd, enum cpu_idle_type idle)
604 /* don't touch RT tasks */
607 static void set_cpus_allowed_rt(struct task_struct *p, cpumask_t *new_mask)
609 int weight = cpus_weight(*new_mask);
614 * Update the migration status of the RQ if we have an RT task
615 * which is running AND changing its weight value.
617 if (p->se.on_rq && (weight != p->nr_cpus_allowed)) {
618 struct rq *rq = task_rq(p);
620 if ((p->nr_cpus_allowed <= 1) && (weight > 1))
621 rq->rt.rt_nr_migratory++;
622 else if((p->nr_cpus_allowed > 1) && (weight <= 1)) {
623 BUG_ON(!rq->rt.rt_nr_migratory);
624 rq->rt.rt_nr_migratory--;
627 update_rt_migration(rq);
630 p->cpus_allowed = *new_mask;
631 p->nr_cpus_allowed = weight;
633 #else /* CONFIG_SMP */
634 # define schedule_tail_balance_rt(rq) do { } while (0)
635 # define schedule_balance_rt(rq, prev) do { } while (0)
636 # define wakeup_balance_rt(rq, p) do { } while (0)
637 #endif /* CONFIG_SMP */
639 static void task_tick_rt(struct rq *rq, struct task_struct *p)
644 * RR tasks need a special form of timeslice management.
645 * FIFO tasks have no timeslices.
647 if (p->policy != SCHED_RR)
653 p->time_slice = DEF_TIMESLICE;
656 * Requeue to the end of queue if we are not the only element
659 if (p->run_list.prev != p->run_list.next) {
660 requeue_task_rt(rq, p);
661 set_tsk_need_resched(p);
665 static void set_curr_task_rt(struct rq *rq)
667 struct task_struct *p = rq->curr;
669 p->se.exec_start = rq->clock;
672 const struct sched_class rt_sched_class = {
673 .next = &fair_sched_class,
674 .enqueue_task = enqueue_task_rt,
675 .dequeue_task = dequeue_task_rt,
676 .yield_task = yield_task_rt,
678 .select_task_rq = select_task_rq_rt,
679 #endif /* CONFIG_SMP */
681 .check_preempt_curr = check_preempt_curr_rt,
683 .pick_next_task = pick_next_task_rt,
684 .put_prev_task = put_prev_task_rt,
687 .load_balance = load_balance_rt,
688 .move_one_task = move_one_task_rt,
689 .set_cpus_allowed = set_cpus_allowed_rt,
692 .set_curr_task = set_curr_task_rt,
693 .task_tick = task_tick_rt,