summaryrefslogtreecommitdiffstats
path: root/kernel/irq/timings.c
blob: 4d2a702d7aa95654acf024e0e67e60c70ec144f1 (plain)
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
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2016, Linaro Ltd - Daniel Lezcano <daniel.lezcano@linaro.org>
#define pr_fmt(fmt) "irq_timings: " fmt

#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/static_key.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/idr.h>
#include <linux/irq.h>
#include <linux/math64.h>
#include <linux/log2.h>

#include <trace/events/irq.h>

#include "internals.h"

DEFINE_STATIC_KEY_FALSE(irq_timing_enabled);

DEFINE_PER_CPU(struct irq_timings, irq_timings);

static DEFINE_IDR(irqt_stats);

void irq_timings_enable(void)
{
	static_branch_enable(&irq_timing_enabled);
}

void irq_timings_disable(void)
{
	static_branch_disable(&irq_timing_enabled);
}

/*
 * The main goal of this algorithm is to predict the next interrupt
 * occurrence on the current CPU.
 *
 * Currently, the interrupt timings are stored in a circular array
 * buffer every time there is an interrupt, as a tuple: the interrupt
 * number and the associated timestamp when the event occurred <irq,
 * timestamp>.
 *
 * For every interrupt occurring in a short period of time, we can
 * measure the elapsed time between the occurrences for the same
 * interrupt and we end up with a suite of intervals. The experience
 * showed the interrupts are often coming following a periodic
 * pattern.
 *
 * The objective of the algorithm is to find out this periodic pattern
 * in a fastest way and use its period to predict the next irq event.
 *
 * When the next interrupt event is requested, we are in the situation
 * where the interrupts are disabled and the circular buffer
 * containing the timings is filled with the events which happened
 * after the previous next-interrupt-event request.
 *
 * At this point, we read the circular buffer and we fill the irq
 * related statistics structure. After this step, the circular array
 * containing the timings is empty because all the values are
 * dispatched in their corresponding buffers.
 *
 * Now for each interrupt, we can predict the next event by using the
 * suffix array, log interval and exponential moving average
 *
 * 1. Suffix array
 *
 * Suffix array is an array of all the suffixes of a string. It is
 * widely used as a data structure for compression, text search, ...
 * For instance for the word 'banana', the suffixes will be: 'banana'
 * 'anana' 'nana' 'ana' 'na' 'a'
 *
 * Usually, the suffix array is sorted but for our purpose it is
 * not necessary and won't provide any improvement in the context of
 * the solved problem where we clearly define the boundaries of the
 * search by a max period and min period.
 *
 * The suffix array will build a suite of intervals of different
 * length and will look for the repetition of each suite. If the suite
 * is repeating then we have the period because it is the length of
 * the suite whatever its position in the buffer.
 *
 * 2. Log interval
 *
 * We saw the irq timings allow to compute the interval of the
 * occurrences for a specific interrupt. We can reasonably assume the
 * longer is the interval, the higher is the error for the next event
 * and we can consider storing those interval values into an array
 * where each slot in the array correspond to an interval at the power
 * of 2 of the index. For example, index 12 will contain values
 * between 2^11 and 2^12.
 *
 * At the end we have an array of values where at each index defines a
 * [2^index - 1, 2 ^ index] interval values allowing to store a large
 * number of values inside a small array.
 *
 * For example, if we have the value 1123, then we store it at
 * ilog2(1123) = 10 index value.
 *
 * Storing those value at the specific index is done by computing an
 * exponential moving average for this specific slot. For instance,
 * for values 1800, 1123, 1453, ... fall under the same slot (10) and
 * the exponential moving average is computed every time a new value
 * is stored at this slot.
 *
 * 3. Exponential Moving Average
 *
 * The EMA is largely used to track a signal for stocks or as a low
 * pass filter. The magic of the formula, is it is very simple and the
 * reactivity of the average can be tuned with the factors called
 * alpha.
 *
 * The higher the alphas are, the faster the average respond to the
 * signal change. In our case, if a slot in the array is a big
 * interval, we can have numbers with a big difference between
 * them. The impact of those differences in the average computation
 * can be tuned by changing the alpha value.
 *
 *
 *  -- The algorithm --
 *
 * We saw the different processing above, now let's see how they are
 * used together.
 *
 * For each interrupt:
 *	For each interval:
 *		Compute the index = ilog2(interval)
 *		Compute a new_ema(buffer[index], interval)
 *		Store the index in a circular buffer
 *
 *	Compute the suffix array of the indexes
 *
 *	For each suffix:
 *		If the suffix is reverse-found 3 times
 *			Return suffix
 *
 *	Return Not found
 *
 * However we can not have endless suffix array to be build, it won't
 * make sense and it will add an extra overhead, so we can restrict
 * this to a maximum suffix length of 5 and a minimum suffix length of
 * 2. The experience showed 5 is the majority of the maximum pattern
 * period found for different devices.
 *
 * The result is a pattern finding less than 1us for an interrupt.
 *
 * Example based on real values:
 *
 * Example 1 : MMC write/read interrupt interval:
 *
 *	223947, 1240, 1384, 1386, 1386,
 *	217416, 1236, 1384, 1386, 1387,
 *	214719, 1241, 1386, 1387, 1384,
 *	213696, 1234, 1384, 1386, 1388,
 *	219904, 1240, 1385, 1389, 1385,
 *	212240, 1240, 1386, 1386, 1386,
 *	214415, 1236, 1384, 1386, 1387,
 *	214276, 1234, 1384, 1388, ?
 *
 * For each element, apply ilog2(value)
 *
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, ?
 *
 * Max period of 5, we take the last (max_period * 3) 15 elements as
 * we can be confident if the pattern repeats itself three times it is
 * a repeating pattern.
 *
 *	             8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, 8,
 *	15, 8, 8, 8, ?
 *
 * Suffixes are:
 *
 *  1) 8, 15, 8, 8, 8  <- max period
 *  2) 8, 15, 8, 8
 *  3) 8, 15, 8
 *  4) 8, 15           <- min period
 *
 * From there we search the repeating pattern for each suffix.
 *
 * buffer: 8, 15, 8, 8, 8, 8, 15, 8, 8, 8, 8, 15, 8, 8, 8
 *         |   |  |  |  |  |   |  |  |  |  |   |  |  |  |
 *         8, 15, 8, 8, 8  |   |  |  |  |  |   |  |  |  |
 *                         8, 15, 8, 8, 8  |   |  |  |  |
 *                                         8, 15, 8, 8, 8
 *
 * When moving the suffix, we found exactly 3 matches.
 *
 * The first suffix with period 5 is repeating.
 *
 * The next event is (3 * max_period) % suffix_period
 *
 * In this example, the result 0, so the next event is suffix[0] => 8
 *
 * However, 8 is the index in the array of exponential moving average
 * which was calculated on the fly when storing the values, so the
 * interval is ema[8] = 1366
 *
 *
 * Example 2:
 *
 *	4, 3, 5, 100,
 *	3, 3, 5, 117,
 *	4, 4, 5, 112,
 *	4, 3, 4, 110,
 *	3, 5, 3, 117,
 *	4, 4, 5, 112,
 *	4, 3, 4, 110,
 *	3, 4, 5, 112,
 *	4, 3, 4, 110
 *
 * ilog2
 *
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4
 *
 * Max period 5:
 *	   0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4,
 *	0, 0, 0, 4
 *
 * Suffixes:
 *
 *  1) 0, 0, 4, 0, 0
 *  2) 0, 0, 4, 0
 *  3) 0, 0, 4
 *  4) 0, 0
 *
 * buffer: 0, 0, 4, 0, 0, 0, 4, 0, 0, 0, 4, 0, 0, 0, 4
 *         |  |  |  |  |  |  X
 *         0, 0, 4, 0, 0, |  X
 *                        0, 0
 *
 * buffer: 0, 0, 4, 0, 0, 0, 4, 0, 0, 0, 4, 0, 0, 0, 4
 *         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
 *         0, 0, 4, 0, |  |  |  |  |  |  |  |  |  |  |
 *                     0, 0, 4, 0, |  |  |  |  |  |  |
 *                                 0, 0, 4, 0, |  |  |
 *                                             0  0  4
 *
 * Pattern is found 3 times, the remaining is 1 which results from
 * (max_period * 3) % suffix_period. This value is the index in the
 * suffix arrays. The suffix array for a period 4 has the value 4
 * at index 1.
 */
#define EMA_ALPHA_VAL		64
#define EMA_ALPHA_SHIFT		7

#define PREDICTION_PERIOD_MIN	3
#define PREDICTION_PERIOD_MAX	5
#define PREDICTION_FACTOR	4
#define PREDICTION_MAX		10 /* 2 ^ PREDICTION_MAX useconds */
#define PREDICTION_BUFFER_SIZE	16 /* slots for EMAs, hardly more than 16 */

/*
 * Number of elements in the circular buffer: If it happens it was
 * flushed before, then the number of elements could be smaller than
 * IRQ_TIMINGS_SIZE, so the count is used, otherwise the array size is
 * used as we wrapped. The index begins from zero when we did not
 * wrap. That could be done in a nicer way with the proper circular
 * array structure type but with the cost of extra computation in the
 * interrupt handler hot path. We choose efficiency.
 */
#define for_each_irqts(i, irqts)					\
	for (i = irqts->count < IRQ_TIMINGS_SIZE ?			\
		     0 : irqts->count & IRQ_TIMINGS_MASK,		\
		     irqts->count = min(IRQ_TIMINGS_SIZE,		\
					irqts->count);			\
	     irqts->count > 0; irqts->count--,				\
		     i = (i + 1) & IRQ_TIMINGS_MASK)

struct irqt_stat {
	u64	last_ts;
	u64	ema_time[PREDICTION_BUFFER_SIZE];
	int	timings[IRQ_TIMINGS_SIZE];
	int	circ_timings[IRQ_TIMINGS_SIZE];
	int	count;
};

/*
 * Exponential moving average computation
 */
static u64 irq_timings_ema_new(u64 value, u64 ema_old)
{
	s64 diff;

	if (unlikely(!ema_old))
		return value;

	diff = (value - ema_old) * EMA_ALPHA_VAL;
	/*
	 * We can use a s64 type variable to be added with the u64
	 * ema_old variable as this one will never have its topmost
	 * bit set, it will be always smaller than 2^63 nanosec
	 * interrupt interval (292 years).
	 */
	return ema_old + (diff >> EMA_ALPHA_SHIFT);
}

static int irq_timings_next_event_index(int *buffer, size_t len, int period_max)
{
	int period;

	/*
	 * Move the beginning pointer to the end minus the max period x 3.
	 * We are at the point we can begin searching the pattern
	 */
	buffer = &buffer[len - (period_max * 3)];

	/* Adjust the length to the maximum allowed period x 3 */
	len = period_max * 3;

	/*
	 * The buffer contains the suite of intervals, in a ilog2
	 * basis, we are looking for a repetition. We point the
	 * beginning of the search three times the length of the
	 * period beginning at the end of the buffer. We do that for
	 * each suffix.
	 */
	for (period = period_max; period >= PREDICTION_PERIOD_MIN; period--) {

		/*
		 * The first comparison always succeed because the
		 * suffix is deduced from the first n-period bytes of
		 * the buffer and we compare the initial suffix with
		 * itself, so we can skip the first iteration.
		 */
		int idx = period;
		size_t size = period;

		/*
		 * We look if the suite with period 'i' repeat
		 * itself. If it is truncated at the end, as it
		 * repeats we can use the period to find out the next
		 * element with the modulo.
		 */
		while (!memcmp(buffer, &buffer[idx], size * sizeof(int))) {

			/*
			 * Move the index in a period basis
			 */
			idx += size;

			/*
			 * If this condition is reached, all previous
			 * memcmp were successful, so the period is
			 * found.
			 */
			if (idx == len)
				return buffer[len % period];

			/*
			 * If the remaining elements to compare are
			 * smaller than the period, readjust the size
			 * of the comparison for the last iteration.
			 */
			if (len - idx < period)
				size = len - idx;
		}
	}

	return -1;
}

static u64 __irq_timings_next_event(struct irqt_stat *irqs, int irq, u64 now)
{
	int index, i, period_max, count, start, min = INT_MAX;

	if ((now - irqs->last_ts) >= NSEC_PER_SEC) {
		irqs->count = irqs->last_ts = 0;
		return U64_MAX;
	}

	/*
	 * As we want to find three times the repetition, we need a
	 * number of intervals greater or equal to three times the
	 * maximum period, otherwise we truncate the max period.
	 */
	period_max = irqs->count > (3 * PREDICTION_PERIOD_MAX) ?
		PREDICTION_PERIOD_MAX : irqs->count / 3;

	/*
	 * If we don't have enough irq timings for this prediction,
	 * just bail out.
	 */
	if (period_max <= PREDICTION_PERIOD_MIN)
		return U64_MAX;

	/*
	 * 'count' will depends if the circular buffer wrapped or not
	 */
	count = irqs->count < IRQ_TIMINGS_SIZE ?
		irqs->count : IRQ_TIMINGS_SIZE;

	start = irqs->count < IRQ_TIMINGS_SIZE ?
		0 : (irqs->count & IRQ_TIMINGS_MASK);

	/*
	 * Copy the content of the circular buffer into another buffer
	 * in order to linearize the buffer instead of dealing with
	 * wrapping indexes and shifted array which will be prone to
	 * error and extremely difficult to debug.
	 */
	for (i = 0; i < count; i++) {
		int index = (start + i) & IRQ_TIMINGS_MASK;

		irqs->timings[i] = irqs->circ_timings[index];
		min = min_t(int, irqs->timings[i], min);
	}

	index = irq_timings_next_event_index(irqs->timings, count, period_max);
	if (index < 0)
		return irqs->last_ts + irqs->ema_time[min];

	return irqs->last_ts + irqs->ema_time[index];
}

static __always_inline int irq_timings_interval_index(u64 interval)
{
	/*
	 * The PREDICTION_FACTOR increase the interval size for the
	 * array of exponential average.
	 */
	u64 interval_us = (interval >> 10) / PREDICTION_FACTOR;

	return likely(interval_us) ? ilog2(interval_us) : 0;
}

static __always_inline void __irq_timings_store(int irq, struct irqt_stat *irqs,
						u64 interval)
{
	int index;

	/*
	 * Get the index in the ema table for this interrupt.
	 */
	index = irq_timings_interval_index(interval);

	if (index > PREDICTION_BUFFER_SIZE - 1) {
		irqs->count = 0;
		return;
	}

	/*
	 * Store the index as an element of the pattern in another
	 * circular array.
	 */
	irqs->circ_timings[irqs->count & IRQ_TIMINGS_MASK] = index;

	irqs->ema_time[index] = irq_timings_ema_new(interval,
						    irqs->ema_time[index]);

	irqs->count++;
}

static inline void irq_timings_store(int irq, struct irqt_stat *irqs, u64 ts)
{
	u64 old_ts = irqs->last_ts;
	u64 interval;

	/*
	 * The timestamps are absolute time values, we need to compute
	 * the timing interval between two interrupts.
	 */
	irqs->last_ts = ts;

	/*
	 * The interval type is u64 in order to deal with the same
	 * type in our computation, that prevent mindfuck issues with
	 * overflow, sign and division.
	 */
	interval = ts - old_ts;

	/*
	 * The interrupt triggered more than one second apart, that
	 * ends the sequence as predictable for our purpose. In this
	 * case, assume we have the beginning of a sequence and the
	 * timestamp is the first value. As it is impossible to
	 * predict anything at this point, return.
	 *
	 * Note the first timestamp of the sequence will always fall
	 * in this test because the old_ts is zero. That is what we
	 * want as we need another timestamp to compute an interval.
	 */
	if (interval >= NSEC_PER_SEC) {
		irqs->count = 0;
		return;
	}

	__irq_timings_store(irq, irqs, interval);
}

/**
 * irq_timings_next_event - Return when the next event is supposed to arrive
 *
 * During the last busy cycle, the number of interrupts is incremented
 * and stored in the irq_timings structure. This information is
 * necessary to:
 *
 * - know if the index in the table wrapped up:
 *
 *      If more than the array size interrupts happened during the
 *      last busy/idle cycle, the index wrapped up and we have to
 *      begin with the next element in the array which is the last one
 *      in the sequence, otherwise it is at the index 0.
 *
 * - have an indication of the interrupts activity on this CPU
 *   (eg. irq/sec)
 *
 * The values are 'consumed' after inserting in the statistical model,
 * thus the count is reinitialized.
 *
 * The array of values **must** be browsed in the time direction, the
 * timestamp must increase between an element and the next one.
 *
 * Returns a nanosec time based estimation of the earliest interrupt,
 * U64_MAX otherwise.
 */
u64 irq_timings_next_event(u64 now)
{
	struct irq_timings *irqts = this_cpu_ptr(&irq_timings);
	struct irqt_stat *irqs;
	struct irqt_stat __percpu *s;
	u64 ts, next_evt = U64_MAX;
	int i, irq = 0;

	/*
	 * This function must be called with the local irq disabled in
	 * order to prevent the timings circular buffer to be updated
	 * while we are reading it.
	 */
	lockdep_assert_irqs_disabled();

	if (!irqts->count)
		return next_evt;

	/*
	 * Number of elements in the circular buffer: If it happens it
	 * was flushed before, then the number of elements could be
	 * smaller than IRQ_TIMINGS_SIZE, so the count is used,
	 * otherwise the array size is used as we wrapped. The index
	 * begins from zero when we did not wrap. That could be done
	 * in a nicer way with the proper circular array structure
	 * type but with the cost of extra computation in the
	 * interrupt handler hot path. We choose efficiency.
	 *
	 * Inject measured irq/timestamp to the pattern prediction
	 * model while decrementing the counter because we consume the
	 * data from our circular buffer.
	 */
	for_each_irqts(i, irqts) {
		irq = irq_timing_decode(irqts->values[i], &ts);
		s = idr_find(&irqt_stats, irq);
		if (s)
			irq_timings_store(irq, this_cpu_ptr(s), ts);
	}

	/*
	 * Look in the list of interrupts' statistics, the earliest
	 * next event.
	 */
	idr_for_each_entry(&irqt_stats, s, i) {

		irqs = this_cpu_ptr(s);

		ts = __irq_timings_next_event(irqs, i, now);
		if (ts <= now)
			return now;

		if (ts < next_evt)
			next_evt = ts;
	}

	return next_evt;
}

void irq_timings_free(int irq)
{
	struct irqt_stat __percpu *s;

	s = idr_find(&irqt_stats, irq);
	if (s) {
		free_percpu(s);
		idr_remove(&irqt_stats, irq);
	}
}

int irq_timings_alloc(int irq)
{
	struct irqt_stat __percpu *s;
	int id;

	/*
	 * Some platforms can have the same private interrupt per cpu,
	 * so this function may be called several times with the
	 * same interrupt number. Just bail out in case the per cpu
	 * stat structure is already allocated.
	 */
	s = idr_find(&irqt_stats, irq);
	if (s)
		return 0;

	s = alloc_percpu(*s);
	if (!s)
		return -ENOMEM;

	idr_preload(GFP_KERNEL);
	id = idr_alloc(&irqt_stats, s, irq, irq + 1, GFP_NOWAIT);
	idr_preload_end();

	if (id < 0) {
		free_percpu(s);
		return id;
	}

	return 0;
}

#ifdef CONFIG_TEST_IRQ_TIMINGS
struct timings_intervals {
	u64 *intervals;
	size_t count;
};

/*
 * Intervals are given in nanosecond base
 */
static u64 intervals0[] __initdata = {
	10000, 50000, 200000, 500000,
	10000, 50000, 200000, 500000,
	10000, 50000, 200000, 500000,
	10000, 50000, 200000, 500000,
	10000, 50000, 200000, 500000,
	10000, 50000, 200000, 500000,
	10000, 50000, 200000, 500000,
	10000, 50000, 200000, 500000,
	10000, 50000, 200000,
};

static u64 intervals1[] __initdata = {
	223947000, 1240000, 1384000, 1386000, 1386000,
	217416000, 1236000, 1384000, 1386000, 1387000,
	214719000, 1241000, 1386000, 1387000, 1384000,
	213696000, 1234000, 1384000, 1386000, 1388000,
	219904000, 1240000, 1385000, 1389000, 1385000,
	212240000, 1240000, 1386000, 1386000, 1386000,
	214415000, 1236000, 1384000, 1386000, 1387000,
	214276000, 1234000,
};

static u64 intervals2[] __initdata = {
	4000, 3000, 5000, 100000,
	3000, 3000, 5000, 117000,
	4000, 4000, 5000, 112000,
	4000, 3000, 4000, 110000,
	3000, 5000, 3000, 117000,
	4000, 4000, 5000, 112000,
	4000, 3000, 4000, 110000,
	3000, 4000, 5000, 112000,
	4000,
};

static u64 intervals3[] __initdata = {
	1385000, 212240000, 1240000,
	1386000, 214415000, 1236000,
	1384000, 214276000, 1234000,
	1386000, 214415000, 1236000,
	1385000, 212240000, 1240000,
	1386000, 214415000, 1236000,
	1384000, 214276000, 1234000,
	1386000, 214415000, 1236000,
	1385000, 212240000, 1240000,
};

static u64 intervals4[] __initdata = {
	10000, 50000, 10000, 50000,
	10000, 50000, 10000, 50000,
	10000, 50000, 10000, 50000,
	10000, 50000, 10000, 50000,
	10000, 50000, 10000, 50000,
	10000, 50000, 10000, 50000,
	10000, 50000, 10000, 50000,
	10000, 50000, 10000, 50000,
	10000,
};

static struct timings_intervals tis[] __initdata = {
	{ intervals0, ARRAY_SIZE(intervals0) },
	{ intervals1, ARRAY_SIZE(intervals1) },
	{ intervals2, ARRAY_SIZE(intervals2) },
	{ intervals3, ARRAY_SIZE(intervals3) },
	{ intervals4, ARRAY_SIZE(intervals4) },
};

static int __init irq_timings_test_next_index(struct timings_intervals *ti)
{
	int _buffer[IRQ_TIMINGS_SIZE];
	int buffer[IRQ_TIMINGS_SIZE];
	int index, start, i, count, period_max;

	count = ti->count - 1;

	period_max = count > (3 * PREDICTION_PERIOD_MAX) ?
		PREDICTION_PERIOD_MAX : count / 3;

	/*
	 * Inject all values except the last one which will be used
	 * to compare with the next index result.
	 */
	pr_debug("index suite: ");

	for (i = 0; i < count; i++) {
		index = irq_timings_interval_index(ti->intervals[i]);
		_buffer[i & IRQ_TIMINGS_MASK] = index;
		pr_cont("%d ", index);
	}

	start = count < IRQ_TIMINGS_SIZE ? 0 :
		count & IRQ_TIMINGS_MASK;

	count = min_t(int, count, IRQ_TIMINGS_SIZE);

	for (i = 0; i < count; i++) {
		int index = (start + i) & IRQ_TIMINGS_MASK;
		buffer[i] = _buffer[index];
	}

	index = irq_timings_next_event_index(buffer, count, period_max);
	i = irq_timings_interval_index(ti->intervals[ti->count - 1]);

	if (index != i) {
		pr_err("Expected (%d) and computed (%d) next indexes differ\n",
		       i, index);
		return -EINVAL;
	}

	return 0;
}

static int __init irq_timings_next_index_selftest(void)
{
	int i, ret;

	for (i = 0; i < ARRAY_SIZE(tis); i++) {

		pr_info("---> Injecting intervals number #%d (count=%zd)\n",
			i, tis[i].count);

		ret = irq_timings_test_next_index(&tis[i]);
		if (ret)
			break;
	}

	return ret;
}

static int __init irq_timings_test_irqs(struct timings_intervals *ti)
{
	struct irqt_stat __percpu *s;
	struct irqt_stat *irqs;
	int i, index, ret, irq = 0xACE5;

	ret = irq_timings_alloc(irq);
	if (ret) {
		pr_err("Failed to allocate irq timings\n");
		return ret;
	}

	s = idr_find(&irqt_stats, irq);
	if (!s) {
		ret = -EIDRM;
		goto out;
	}

	irqs = this_cpu_ptr(s);

	for (i = 0; i < ti->count; i++) {

		index = irq_timings_interval_index(ti->intervals[i]);
		pr_debug("%d: interval=%llu ema_index=%d\n",
			 i, ti->intervals[i], index);

		__irq_timings_store(irq, irqs, ti->intervals[i]);
		if (irqs->circ_timings[i & IRQ_TIMINGS_MASK] != index) {
			pr_err("Failed to store in the circular buffer\n");
			goto out;
		}
	}

	if (irqs->count != ti->count) {
		pr_err("Count differs\n");
		goto out;
	}

	ret = 0;
out:
	irq_timings_free(irq);

	return ret;
}

static int __init irq_timings_irqs_selftest(void)
{
	int i, ret;

	for (i = 0; i < ARRAY_SIZE(tis); i++) {
		pr_info("---> Injecting intervals number #%d (count=%zd)\n",
			i, tis[i].count);
		ret = irq_timings_test_irqs(&tis[i]);
		if (ret)
			break;
	}

	return ret;
}

static int __init irq_timings_test_irqts(struct irq_timings *irqts,
					 unsigned count)
{
	int start = count >= IRQ_TIMINGS_SIZE ? count - IRQ_TIMINGS_SIZE : 0;
	int i, irq, oirq = 0xBEEF;
	u64 ots = 0xDEAD, ts;

	/*
	 * Fill the circular buffer by using the dedicated function.
	 */
	for (i = 0; i < count; i++) {
		pr_debug("%d: index=%d, ts=%llX irq=%X\n",
			 i, i & IRQ_TIMINGS_MASK, ots + i, oirq + i);

		irq_timings_push(ots + i, oirq + i);
	}

	/*
	 * Compute the first elements values after the index wrapped
	 * up or not.
	 */
	ots += start;
	oirq += start;

	/*
	 * Test the circular buffer count is correct.
	 */
	pr_debug("---> Checking timings array count (%d) is right\n", count);
	if (WARN_ON(irqts->count != count))
		return -EINVAL;

	/*
	 * Test the macro allowing to browse all the irqts.
	 */
	pr_debug("---> Checking the for_each_irqts() macro\n");
	for_each_irqts(i, irqts) {

		irq = irq_timing_decode(irqts->values[i], &ts);

		pr_debug("index=%d, ts=%llX / %llX, irq=%X / %X\n",
			 i, ts, ots, irq, oirq);

		if (WARN_ON(ts != ots || irq != oirq))
			return -EINVAL;

		ots++; oirq++;
	}

	/*
	 * The circular buffer should have be flushed when browsed
	 * with for_each_irqts
	 */
	pr_debug("---> Checking timings array is empty after browsing it\n");
	if (WARN_ON(irqts->count))
		return -EINVAL;

	return 0;
}

static int __init irq_timings_irqts_selftest(void)
{
	struct irq_timings *irqts = this_cpu_ptr(&irq_timings);
	int i, ret;

	/*
	 * Test the circular buffer with different number of
	 * elements. The purpose is to test at the limits (empty, half
	 * full, full, wrapped with the cursor at the boundaries,
	 * wrapped several times, etc ...
	 */
	int count[] = { 0,
			IRQ_TIMINGS_SIZE >> 1,
			IRQ_TIMINGS_SIZE,
			IRQ_TIMINGS_SIZE + (IRQ_TIMINGS_SIZE >> 1),
			2 * IRQ_TIMINGS_SIZE,
			(2 * IRQ_TIMINGS_SIZE) + 3,
	};

	for (i = 0; i < ARRAY_SIZE(count); i++) {

		pr_info("---> Checking the timings with %d/%d values\n",
			count[i], IRQ_TIMINGS_SIZE);

		ret = irq_timings_test_irqts(irqts, count[i]);
		if (ret)
			break;
	}

	return ret;
}

static int __init irq_timings_selftest(void)
{
	int ret;

	pr_info("------------------- selftest start -----------------\n");

	/*
	 * At this point, we don't except any subsystem to use the irq
	 * timings but us, so it should not be enabled.
	 */
	if (static_branch_unlikely(&irq_timing_enabled)) {
		pr_warn("irq timings already initialized, skipping selftest\n");
		return 0;
	}

	ret = irq_timings_irqts_selftest();
	if (ret)
		goto out;

	ret = irq_timings_irqs_selftest();
	if (ret)
		goto out;

	ret = irq_timings_next_index_selftest();
out:
	pr_info("---------- selftest end with %s -----------\n",
		ret ? "failure" : "success");

	return ret;
}
early_initcall(irq_timings_selftest);
#endif