sched: clean up this_rq use in kernel/sched_rt.c
[linux-2.6.git] / kernel / sched_rt.c
1 /*
2  * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
3  * policies)
4  */
5
6 #ifdef CONFIG_SMP
7 static cpumask_t rt_overload_mask;
8 static atomic_t rto_count;
9 static inline int rt_overloaded(void)
10 {
11         return atomic_read(&rto_count);
12 }
13 static inline cpumask_t *rt_overload(void)
14 {
15         return &rt_overload_mask;
16 }
17 static inline void rt_set_overload(struct rq *rq)
18 {
19         cpu_set(rq->cpu, rt_overload_mask);
20         /*
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
25          * updated yet.
26          */
27         wmb();
28         atomic_inc(&rto_count);
29 }
30 static inline void rt_clear_overload(struct rq *rq)
31 {
32         /* the order here really doesn't matter */
33         atomic_dec(&rto_count);
34         cpu_clear(rq->cpu, rt_overload_mask);
35 }
36
37 static void update_rt_migration(struct rq *rq)
38 {
39         if (rq->rt.rt_nr_migratory && (rq->rt.rt_nr_running > 1))
40                 rt_set_overload(rq);
41         else
42                 rt_clear_overload(rq);
43 }
44 #endif /* CONFIG_SMP */
45
46 /*
47  * Update the current task's runtime statistics. Skip current tasks that
48  * are not in our scheduling class.
49  */
50 static void update_curr_rt(struct rq *rq)
51 {
52         struct task_struct *curr = rq->curr;
53         u64 delta_exec;
54
55         if (!task_has_rt_policy(curr))
56                 return;
57
58         delta_exec = rq->clock - curr->se.exec_start;
59         if (unlikely((s64)delta_exec < 0))
60                 delta_exec = 0;
61
62         schedstat_set(curr->se.exec_max, max(curr->se.exec_max, delta_exec));
63
64         curr->se.sum_exec_runtime += delta_exec;
65         curr->se.exec_start = rq->clock;
66         cpuacct_charge(curr, delta_exec);
67 }
68
69 static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
70 {
71         WARN_ON(!rt_task(p));
72         rq->rt.rt_nr_running++;
73 #ifdef CONFIG_SMP
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++;
78
79         update_rt_migration(rq);
80 #endif /* CONFIG_SMP */
81 }
82
83 static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
84 {
85         WARN_ON(!rt_task(p));
86         WARN_ON(!rq->rt.rt_nr_running);
87         rq->rt.rt_nr_running--;
88 #ifdef CONFIG_SMP
89         if (rq->rt.rt_nr_running) {
90                 struct rt_prio_array *array;
91
92                 WARN_ON(p->prio < rq->rt.highest_prio);
93                 if (p->prio == rq->rt.highest_prio) {
94                         /* recalculate */
95                         array = &rq->rt.active;
96                         rq->rt.highest_prio =
97                                 sched_find_first_bit(array->bitmap);
98                 } /* otherwise leave rq->highest prio alone */
99         } else
100                 rq->rt.highest_prio = MAX_RT_PRIO;
101         if (p->nr_cpus_allowed > 1)
102                 rq->rt.rt_nr_migratory--;
103
104         update_rt_migration(rq);
105 #endif /* CONFIG_SMP */
106 }
107
108 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
109 {
110         struct rt_prio_array *array = &rq->rt.active;
111
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);
115
116         inc_rt_tasks(p, rq);
117 }
118
119 /*
120  * Adding/removing a task to/from a priority array:
121  */
122 static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
123 {
124         struct rt_prio_array *array = &rq->rt.active;
125
126         update_curr_rt(rq);
127
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);
132
133         dec_rt_tasks(p, rq);
134 }
135
136 /*
137  * Put task to the end of the run list without the overhead of dequeue
138  * followed by enqueue.
139  */
140 static void requeue_task_rt(struct rq *rq, struct task_struct *p)
141 {
142         struct rt_prio_array *array = &rq->rt.active;
143
144         list_move_tail(&p->run_list, array->queue + p->prio);
145 }
146
147 static void
148 yield_task_rt(struct rq *rq)
149 {
150         requeue_task_rt(rq, rq->curr);
151 }
152
153 /*
154  * Preempt the current task with a newly woken task if needed:
155  */
156 static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
157 {
158         if (p->prio < rq->curr->prio)
159                 resched_task(rq->curr);
160 }
161
162 static struct task_struct *pick_next_task_rt(struct rq *rq)
163 {
164         struct rt_prio_array *array = &rq->rt.active;
165         struct task_struct *next;
166         struct list_head *queue;
167         int idx;
168
169         idx = sched_find_first_bit(array->bitmap);
170         if (idx >= MAX_RT_PRIO)
171                 return NULL;
172
173         queue = array->queue + idx;
174         next = list_entry(queue->next, struct task_struct, run_list);
175
176         next->se.exec_start = rq->clock;
177
178         return next;
179 }
180
181 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
182 {
183         update_curr_rt(rq);
184         p->se.exec_start = 0;
185 }
186
187 #ifdef CONFIG_SMP
188 /* Only try algorithms three times */
189 #define RT_MAX_TRIES 3
190
191 static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
192 static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
193
194 static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
195 {
196         if (!task_running(rq, p) &&
197             (cpu < 0 || cpu_isset(cpu, p->cpus_allowed)) &&
198             (p->nr_cpus_allowed > 1))
199                 return 1;
200         return 0;
201 }
202
203 /* Return the second highest RT task, NULL otherwise */
204 static struct task_struct *pick_next_highest_task_rt(struct rq *rq,
205                                                      int cpu)
206 {
207         struct rt_prio_array *array = &rq->rt.active;
208         struct task_struct *next;
209         struct list_head *queue;
210         int idx;
211
212         assert_spin_locked(&rq->lock);
213
214         if (likely(rq->rt.rt_nr_running < 2))
215                 return NULL;
216
217         idx = sched_find_first_bit(array->bitmap);
218         if (unlikely(idx >= MAX_RT_PRIO)) {
219                 WARN_ON(1); /* rt_nr_running is bad */
220                 return NULL;
221         }
222
223         queue = array->queue + idx;
224         BUG_ON(list_empty(queue));
225
226         next = list_entry(queue->next, struct task_struct, run_list);
227         if (unlikely(pick_rt_task(rq, next, cpu)))
228                 goto out;
229
230         if (queue->next->next != queue) {
231                 /* same prio task */
232                 next = list_entry(queue->next->next, struct task_struct, run_list);
233                 if (pick_rt_task(rq, next, cpu))
234                         goto out;
235         }
236
237  retry:
238         /* slower, but more flexible */
239         idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
240         if (unlikely(idx >= MAX_RT_PRIO))
241                 return NULL;
242
243         queue = array->queue + idx;
244         BUG_ON(list_empty(queue));
245
246         list_for_each_entry(next, queue, run_list) {
247                 if (pick_rt_task(rq, next, cpu))
248                         goto out;
249         }
250
251         goto retry;
252
253  out:
254         return next;
255 }
256
257 static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
258
259 /* Will lock the rq it finds */
260 static struct rq *find_lock_lowest_rq(struct task_struct *task,
261                                       struct rq *this_rq)
262 {
263         struct rq *lowest_rq = NULL;
264         int cpu;
265         int tries;
266         cpumask_t *cpu_mask = &__get_cpu_var(local_cpu_mask);
267
268         cpus_and(*cpu_mask, cpu_online_map, task->cpus_allowed);
269
270         for (tries = 0; tries < RT_MAX_TRIES; tries++) {
271                 /*
272                  * Scan each rq for the lowest prio.
273                  */
274                 for_each_cpu_mask(cpu, *cpu_mask) {
275                         struct rq *rq = &per_cpu(runqueues, cpu);
276
277                         if (cpu == this_rq->cpu)
278                                 continue;
279
280                         /* We look for lowest RT prio or non-rt CPU */
281                         if (rq->rt.highest_prio >= MAX_RT_PRIO) {
282                                 lowest_rq = rq;
283                                 break;
284                         }
285
286                         /* no locking for now */
287                         if (rq->rt.highest_prio > task->prio &&
288                             (!lowest_rq || rq->rt.highest_prio > lowest_rq->rt.highest_prio)) {
289                                 lowest_rq = rq;
290                         }
291                 }
292
293                 if (!lowest_rq)
294                         break;
295
296                 /* if the prio of this runqueue changed, try again */
297                 if (double_lock_balance(this_rq, lowest_rq)) {
298                         /*
299                          * We had to unlock the run queue. In
300                          * the mean time, task could have
301                          * migrated already or had its affinity changed.
302                          * Also make sure that it wasn't scheduled on its rq.
303                          */
304                         if (unlikely(task_rq(task) != this_rq ||
305                                      !cpu_isset(lowest_rq->cpu, task->cpus_allowed) ||
306                                      task_running(this_rq, task) ||
307                                      !task->se.on_rq)) {
308                                 spin_unlock(&lowest_rq->lock);
309                                 lowest_rq = NULL;
310                                 break;
311                         }
312                 }
313
314                 /* If this rq is still suitable use it. */
315                 if (lowest_rq->rt.highest_prio > task->prio)
316                         break;
317
318                 /* try again */
319                 spin_unlock(&lowest_rq->lock);
320                 lowest_rq = NULL;
321         }
322
323         return lowest_rq;
324 }
325
326 /*
327  * If the current CPU has more than one RT task, see if the non
328  * running task can migrate over to a CPU that is running a task
329  * of lesser priority.
330  */
331 static int push_rt_task(struct rq *rq)
332 {
333         struct task_struct *next_task;
334         struct rq *lowest_rq;
335         int ret = 0;
336         int paranoid = RT_MAX_TRIES;
337
338         assert_spin_locked(&rq->lock);
339
340         next_task = pick_next_highest_task_rt(rq, -1);
341         if (!next_task)
342                 return 0;
343
344  retry:
345         if (unlikely(next_task == rq->curr)) {
346                 WARN_ON(1);
347                 return 0;
348         }
349
350         /*
351          * It's possible that the next_task slipped in of
352          * higher priority than current. If that's the case
353          * just reschedule current.
354          */
355         if (unlikely(next_task->prio < rq->curr->prio)) {
356                 resched_task(rq->curr);
357                 return 0;
358         }
359
360         /* We might release rq lock */
361         get_task_struct(next_task);
362
363         /* find_lock_lowest_rq locks the rq if found */
364         lowest_rq = find_lock_lowest_rq(next_task, rq);
365         if (!lowest_rq) {
366                 struct task_struct *task;
367                 /*
368                  * find lock_lowest_rq releases rq->lock
369                  * so it is possible that next_task has changed.
370                  * If it has, then try again.
371                  */
372                 task = pick_next_highest_task_rt(rq, -1);
373                 if (unlikely(task != next_task) && task && paranoid--) {
374                         put_task_struct(next_task);
375                         next_task = task;
376                         goto retry;
377                 }
378                 goto out;
379         }
380
381         assert_spin_locked(&lowest_rq->lock);
382
383         deactivate_task(rq, next_task, 0);
384         set_task_cpu(next_task, lowest_rq->cpu);
385         activate_task(lowest_rq, next_task, 0);
386
387         resched_task(lowest_rq->curr);
388
389         spin_unlock(&lowest_rq->lock);
390
391         ret = 1;
392 out:
393         put_task_struct(next_task);
394
395         return ret;
396 }
397
398 /*
399  * TODO: Currently we just use the second highest prio task on
400  *       the queue, and stop when it can't migrate (or there's
401  *       no more RT tasks).  There may be a case where a lower
402  *       priority RT task has a different affinity than the
403  *       higher RT task. In this case the lower RT task could
404  *       possibly be able to migrate where as the higher priority
405  *       RT task could not.  We currently ignore this issue.
406  *       Enhancements are welcome!
407  */
408 static void push_rt_tasks(struct rq *rq)
409 {
410         /* push_rt_task will return true if it moved an RT */
411         while (push_rt_task(rq))
412                 ;
413 }
414
415 static int pull_rt_task(struct rq *this_rq)
416 {
417         struct task_struct *next;
418         struct task_struct *p;
419         struct rq *src_rq;
420         cpumask_t *rto_cpumask;
421         int this_cpu = this_rq->cpu;
422         int cpu;
423         int ret = 0;
424
425         assert_spin_locked(&this_rq->lock);
426
427         /*
428          * If cpusets are used, and we have overlapping
429          * run queue cpusets, then this algorithm may not catch all.
430          * This is just the price you pay on trying to keep
431          * dirtying caches down on large SMP machines.
432          */
433         if (likely(!rt_overloaded()))
434                 return 0;
435
436         next = pick_next_task_rt(this_rq);
437
438         rto_cpumask = rt_overload();
439
440         for_each_cpu_mask(cpu, *rto_cpumask) {
441                 if (this_cpu == cpu)
442                         continue;
443
444                 src_rq = cpu_rq(cpu);
445                 if (unlikely(src_rq->rt.rt_nr_running <= 1)) {
446                         /*
447                          * It is possible that overlapping cpusets
448                          * will miss clearing a non overloaded runqueue.
449                          * Clear it now.
450                          */
451                         if (double_lock_balance(this_rq, src_rq)) {
452                                 /* unlocked our runqueue lock */
453                                 struct task_struct *old_next = next;
454                                 next = pick_next_task_rt(this_rq);
455                                 if (next != old_next)
456                                         ret = 1;
457                         }
458                         if (likely(src_rq->rt.rt_nr_running <= 1))
459                                 /*
460                                  * Small chance that this_rq->curr changed
461                                  * but it's really harmless here.
462                                  */
463                                 rt_clear_overload(this_rq);
464                         else
465                                 /*
466                                  * Heh, the src_rq is now overloaded, since
467                                  * we already have the src_rq lock, go straight
468                                  * to pulling tasks from it.
469                                  */
470                                 goto try_pulling;
471                         spin_unlock(&src_rq->lock);
472                         continue;
473                 }
474
475                 /*
476                  * We can potentially drop this_rq's lock in
477                  * double_lock_balance, and another CPU could
478                  * steal our next task - hence we must cause
479                  * the caller to recalculate the next task
480                  * in that case:
481                  */
482                 if (double_lock_balance(this_rq, src_rq)) {
483                         struct task_struct *old_next = next;
484                         next = pick_next_task_rt(this_rq);
485                         if (next != old_next)
486                                 ret = 1;
487                 }
488
489                 /*
490                  * Are there still pullable RT tasks?
491                  */
492                 if (src_rq->rt.rt_nr_running <= 1) {
493                         spin_unlock(&src_rq->lock);
494                         continue;
495                 }
496
497  try_pulling:
498                 p = pick_next_highest_task_rt(src_rq, this_cpu);
499
500                 /*
501                  * Do we have an RT task that preempts
502                  * the to-be-scheduled task?
503                  */
504                 if (p && (!next || (p->prio < next->prio))) {
505                         WARN_ON(p == src_rq->curr);
506                         WARN_ON(!p->se.on_rq);
507
508                         /*
509                          * There's a chance that p is higher in priority
510                          * than what's currently running on its cpu.
511                          * This is just that p is wakeing up and hasn't
512                          * had a chance to schedule. We only pull
513                          * p if it is lower in priority than the
514                          * current task on the run queue or
515                          * this_rq next task is lower in prio than
516                          * the current task on that rq.
517                          */
518                         if (p->prio < src_rq->curr->prio ||
519                             (next && next->prio < src_rq->curr->prio))
520                                 goto bail;
521
522                         ret = 1;
523
524                         deactivate_task(src_rq, p, 0);
525                         set_task_cpu(p, this_cpu);
526                         activate_task(this_rq, p, 0);
527                         /*
528                          * We continue with the search, just in
529                          * case there's an even higher prio task
530                          * in another runqueue. (low likelyhood
531                          * but possible)
532                          */
533
534                         /*
535                          * Update next so that we won't pick a task
536                          * on another cpu with a priority lower (or equal)
537                          * than the one we just picked.
538                          */
539                         next = p;
540
541                 }
542  bail:
543                 spin_unlock(&src_rq->lock);
544         }
545
546         return ret;
547 }
548
549 static void schedule_balance_rt(struct rq *rq,
550                                 struct task_struct *prev)
551 {
552         /* Try to pull RT tasks here if we lower this rq's prio */
553         if (unlikely(rt_task(prev)) &&
554             rq->rt.highest_prio > prev->prio)
555                 pull_rt_task(rq);
556 }
557
558 static void schedule_tail_balance_rt(struct rq *rq)
559 {
560         /*
561          * If we have more than one rt_task queued, then
562          * see if we can push the other rt_tasks off to other CPUS.
563          * Note we may release the rq lock, and since
564          * the lock was owned by prev, we need to release it
565          * first via finish_lock_switch and then reaquire it here.
566          */
567         if (unlikely(rq->rt.rt_nr_running > 1)) {
568                 spin_lock_irq(&rq->lock);
569                 push_rt_tasks(rq);
570                 spin_unlock_irq(&rq->lock);
571         }
572 }
573
574
575 static void wakeup_balance_rt(struct rq *rq, struct task_struct *p)
576 {
577         if (unlikely(rt_task(p)) &&
578             !task_running(rq, p) &&
579             (p->prio >= rq->curr->prio))
580                 push_rt_tasks(rq);
581 }
582
583 static unsigned long
584 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
585                 unsigned long max_load_move,
586                 struct sched_domain *sd, enum cpu_idle_type idle,
587                 int *all_pinned, int *this_best_prio)
588 {
589         /* don't touch RT tasks */
590         return 0;
591 }
592
593 static int
594 move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
595                  struct sched_domain *sd, enum cpu_idle_type idle)
596 {
597         /* don't touch RT tasks */
598         return 0;
599 }
600 static void set_cpus_allowed_rt(struct task_struct *p, cpumask_t *new_mask)
601 {
602         int weight = cpus_weight(*new_mask);
603
604         BUG_ON(!rt_task(p));
605
606         /*
607          * Update the migration status of the RQ if we have an RT task
608          * which is running AND changing its weight value.
609          */
610         if (p->se.on_rq && (weight != p->nr_cpus_allowed)) {
611                 struct rq *rq = task_rq(p);
612
613                 if ((p->nr_cpus_allowed <= 1) && (weight > 1))
614                         rq->rt.rt_nr_migratory++;
615                 else if((p->nr_cpus_allowed > 1) && (weight <= 1)) {
616                         BUG_ON(!rq->rt.rt_nr_migratory);
617                         rq->rt.rt_nr_migratory--;
618                 }
619
620                 update_rt_migration(rq);
621         }
622
623         p->cpus_allowed    = *new_mask;
624         p->nr_cpus_allowed = weight;
625 }
626 #else /* CONFIG_SMP */
627 # define schedule_tail_balance_rt(rq)   do { } while (0)
628 # define schedule_balance_rt(rq, prev)  do { } while (0)
629 # define wakeup_balance_rt(rq, p)       do { } while (0)
630 #endif /* CONFIG_SMP */
631
632 static void task_tick_rt(struct rq *rq, struct task_struct *p)
633 {
634         update_curr_rt(rq);
635
636         /*
637          * RR tasks need a special form of timeslice management.
638          * FIFO tasks have no timeslices.
639          */
640         if (p->policy != SCHED_RR)
641                 return;
642
643         if (--p->time_slice)
644                 return;
645
646         p->time_slice = DEF_TIMESLICE;
647
648         /*
649          * Requeue to the end of queue if we are not the only element
650          * on the queue:
651          */
652         if (p->run_list.prev != p->run_list.next) {
653                 requeue_task_rt(rq, p);
654                 set_tsk_need_resched(p);
655         }
656 }
657
658 static void set_curr_task_rt(struct rq *rq)
659 {
660         struct task_struct *p = rq->curr;
661
662         p->se.exec_start = rq->clock;
663 }
664
665 const struct sched_class rt_sched_class = {
666         .next                   = &fair_sched_class,
667         .enqueue_task           = enqueue_task_rt,
668         .dequeue_task           = dequeue_task_rt,
669         .yield_task             = yield_task_rt,
670
671         .check_preempt_curr     = check_preempt_curr_rt,
672
673         .pick_next_task         = pick_next_task_rt,
674         .put_prev_task          = put_prev_task_rt,
675
676 #ifdef CONFIG_SMP
677         .load_balance           = load_balance_rt,
678         .move_one_task          = move_one_task_rt,
679         .set_cpus_allowed       = set_cpus_allowed_rt,
680 #endif
681
682         .set_curr_task          = set_curr_task_rt,
683         .task_tick              = task_tick_rt,
684 };