aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/sched_rt.c
blob: 52d88f193afcc044a2e14c4bc27c4901c45aa3c6 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
/*
 * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
 * policies)
 */

#ifdef CONFIG_SMP
static cpumask_t rt_overload_mask;
static atomic_t rto_count;
static inline int rt_overloaded(void)
{
	return atomic_read(&rto_count);
}
static inline cpumask_t *rt_overload(void)
{
	return &rt_overload_mask;
}
static inline void rt_set_overload(struct rq *rq)
{
	rq->rt.overloaded = 1;
	cpu_set(rq->cpu, rt_overload_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(&rto_count);
}
static inline void rt_clear_overload(struct rq *rq)
{
	/* the order here really doesn't matter */
	atomic_dec(&rto_count);
	cpu_clear(rq->cpu, rt_overload_mask);
	rq->rt.overloaded = 0;
}

static void update_rt_migration(struct rq *rq)
{
	if (rq->rt.rt_nr_migratory && (rq->rt.rt_nr_running > 1))
		rt_set_overload(rq);
	else
		rt_clear_overload(rq);
}
#endif /* CONFIG_SMP */

/*
 * 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;
	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);
}

static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
{
	WARN_ON(!rt_task(p));
	rq->rt.rt_nr_running++;
#ifdef CONFIG_SMP
	if (p->prio < rq->rt.highest_prio)
		rq->rt.highest_prio = p->prio;
	if (p->nr_cpus_allowed > 1)
		rq->rt.rt_nr_migratory++;

	update_rt_migration(rq);
#endif /* CONFIG_SMP */
}

static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
{
	WARN_ON(!rt_task(p));
	WARN_ON(!rq->rt.rt_nr_running);
	rq->rt.rt_nr_running--;
#ifdef CONFIG_SMP
	if (rq->rt.rt_nr_running) {
		struct rt_prio_array *array;

		WARN_ON(p->prio < rq->rt.highest_prio);
		if (p->prio == rq->rt.highest_prio) {
			/* recalculate */
			array = &rq->rt.active;
			rq->rt.highest_prio =
				sched_find_first_bit(array->bitmap);
		} /* otherwise leave rq->highest prio alone */
	} else
		rq->rt.highest_prio = MAX_RT_PRIO;
	if (p->nr_cpus_allowed > 1)
		rq->rt.rt_nr_migratory--;

	update_rt_migration(rq);
#endif /* CONFIG_SMP */
}

static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
{
	struct rt_prio_array *array = &rq->rt.active;

	list_add_tail(&p->run_list, array->queue + p->prio);
	__set_bit(p->prio, array->bitmap);
	inc_cpu_load(rq, p->se.load.weight);

	inc_rt_tasks(p, rq);
}

/*
 * Adding/removing a task to/from a priority array:
 */
static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
{
	struct rt_prio_array *array = &rq->rt.active;

	update_curr_rt(rq);

	list_del(&p->run_list);
	if (list_empty(array->queue + p->prio))
		__clear_bit(p->prio, array->bitmap);
	dec_cpu_load(rq, p->se.load.weight);

	dec_rt_tasks(p, rq);
}

/*
 * Put task to the end of the run list without the overhead of dequeue
 * followed by enqueue.
 */
static void requeue_task_rt(struct rq *rq, struct task_struct *p)
{
	struct rt_prio_array *array = &rq->rt.active;

	list_move_tail(&p->run_list, array->queue + p->prio);
}

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->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 task_struct *pick_next_task_rt(struct rq *rq)
{
	struct rt_prio_array *array = &rq->rt.active;
	struct task_struct *next;
	struct list_head *queue;
	int idx;

	idx = sched_find_first_bit(array->bitmap);
	if (idx >= MAX_RT_PRIO)
		return NULL;

	queue = array->queue + idx;
	next = list_entry(queue->next, struct task_struct, run_list);

	next->se.exec_start = rq->clock;

	return next;
}

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->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 rt_prio_array *array = &rq->rt.active;
	struct task_struct *next;
	struct list_head *queue;
	int idx;

	assert_spin_locked(&rq->lock);

	if (likely(rq->rt.rt_nr_running < 2))
		return NULL;

	idx = sched_find_first_bit(array->bitmap);
	if (unlikely(idx >= MAX_RT_PRIO)) {
		WARN_ON(1); /* rt_nr_running is bad */
		return NULL;
	}

	queue = array->queue + idx;
	BUG_ON(list_empty(queue));

	next = list_entry(queue->next, struct task_struct, run_list);
	if (unlikely(pick_rt_task(rq, next, cpu)))
		goto out;

	if (queue->next->next != queue) {
		/* same prio task */
		next = list_entry(queue->next->next, struct task_struct, run_list);
		if (pick_rt_task(rq, next, cpu))
			goto out;
	}

 retry:
	/* slower, but more flexible */
	idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
	if (unlikely(idx >= MAX_RT_PRIO))
		return NULL;

	queue = array->queue + idx;
	BUG_ON(list_empty(queue));

	list_for_each_entry(next, queue, run_list) {
		if (pick_rt_task(rq, next, cpu))
			goto out;
	}

	goto retry;

 out:
	return next;
}

static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
static DEFINE_PER_CPU(cpumask_t, valid_cpu_mask);

static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
{
	int       cpu;
	cpumask_t *valid_mask = &__get_cpu_var(valid_cpu_mask);
	int       lowest_prio = -1;
	int       count       = 0;

	cpus_clear(*lowest_mask);
	cpus_and(*valid_mask, cpu_online_map, task->cpus_allowed);

	/*
	 * Scan each rq for the lowest prio.
	 */
	for_each_cpu_mask(cpu, *valid_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 (count)
				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;
				if (count) {
					cpus_clear(*lowest_mask);
					count = 0;
				}
			}
			cpu_set(rq->cpu, *lowest_mask);
			count++;
		}
	}

	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 cpu;
	int tries;

	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;

	assert_spin_locked(&rq->lock);

	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;
	}

	assert_spin_locked(&lowest_rq->lock);

	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)
{
	struct task_struct *next;
	struct task_struct *p;
	struct rq *src_rq;
	cpumask_t *rto_cpumask;
	int this_cpu = this_rq->cpu;
	int cpu;
	int ret = 0;

	assert_spin_locked(&this_rq->lock);

	/*
	 * If cpusets are used, and we have overlapping
	 * run queue cpusets, then this algorithm may not catch all.
	 * This is just the price you pay on trying to keep
	 * dirtying caches down on large SMP machines.
	 */
	if (likely(!rt_overloaded()))
		return 0;

	next = pick_next_task_rt(this_rq);

	rto_cpumask = rt_overload();

	for_each_cpu_mask(cpu, *rto_cpumask) {
		if (this_cpu == cpu)
			continue;

		src_rq = cpu_rq(cpu);
		if (unlikely(src_rq->rt.rt_nr_running <= 1)) {
			/*
			 * It is possible that overlapping cpusets
			 * will miss clearing a non overloaded runqueue.
			 * Clear it now.
			 */
			if (double_lock_balance(this_rq, src_rq)) {
				/* unlocked our runqueue lock */
				struct task_struct *old_next = next;
				next = pick_next_task_rt(this_rq);
				if (next != old_next)
					ret = 1;
			}
			if (likely(src_rq->rt.rt_nr_running <= 1))
				/*
				 * Small chance that this_rq->curr changed
				 * but it's really harmless here.
				 */
				rt_clear_overload(this_rq);
			else
				/*
				 * Heh, the src_rq is now overloaded, since
				 * we already have the src_rq lock, go straight
				 * to pulling tasks from it.
				 */
				goto try_pulling;
			spin_unlock(&src_rq->lock);
			continue;
		}

		/*
		 * 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) {
			spin_unlock(&src_rq->lock);
			continue;
		}

 try_pulling:
		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 bail;

			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;

		}
 bail:
		spin_unlock(&src_rq->lock);
	}

	return ret;
}

static void schedule_balance_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 schedule_tail_balance_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);
	}
}


static void wakeup_balance_rt(struct rq *rq, struct task_struct *p)
{
	if (unlikely(rt_task(p)) &&
	    !task_running(rq, p) &&
	    (p->prio >= rq->rt.highest_prio) &&
	    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, 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->nr_cpus_allowed)) {
		struct rq *rq = task_rq(p);

		if ((p->nr_cpus_allowed <= 1) && (weight > 1))
			rq->rt.rt_nr_migratory++;
		else if((p->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->nr_cpus_allowed = weight;
}
#else /* CONFIG_SMP */
# define schedule_tail_balance_rt(rq)	do { } while (0)
# define schedule_balance_rt(rq, prev)	do { } while (0)
# define wakeup_balance_rt(rq, p)	do { } while (0)
#endif /* CONFIG_SMP */

static void task_tick_rt(struct rq *rq, struct task_struct *p)
{
	update_curr_rt(rq);

	/*
	 * RR tasks need a special form of timeslice management.
	 * FIFO tasks have no timeslices.
	 */
	if (p->policy != SCHED_RR)
		return;

	if (--p->time_slice)
		return;

	p->time_slice = DEF_TIMESLICE;

	/*
	 * Requeue to the end of queue if we are not the only element
	 * on the queue:
	 */
	if (p->run_list.prev != p->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;
}

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,
#endif

	.set_curr_task          = set_curr_task_rt,
	.task_tick		= task_tick_rt,
};