Training courses

Kernel and Embedded Linux

Bootlin training courses

Embedded Linux, kernel,
Yocto Project, Buildroot, real-time,
graphics, boot time, debugging...

Bootlin logo

Elixir Cross Referencer

   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
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
/*
 *  linux/kernel/time/tick-sched.c
 *
 *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
 *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
 *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
 *
 *  No idle tick implementation for low and high resolution timers
 *
 *  Started by: Thomas Gleixner and Ingo Molnar
 *
 *  Distribute under GPLv2.
 */
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/irq_work.h>
#include <linux/posix-timers.h>
#include <linux/context_tracking.h>

#include <asm/irq_regs.h>

#include "tick-internal.h"

#include <trace/events/timer.h>

/*
 * Per-CPU nohz control structure
 */
static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);

struct tick_sched *tick_get_tick_sched(int cpu)
{
	return &per_cpu(tick_cpu_sched, cpu);
}

#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
/*
 * The time, when the last jiffy update happened. Protected by jiffies_lock.
 */
static ktime_t last_jiffies_update;

/*
 * Must be called with interrupts disabled !
 */
static void tick_do_update_jiffies64(ktime_t now)
{
	unsigned long ticks = 0;
	ktime_t delta;

	/*
	 * Do a quick check without holding jiffies_lock:
	 */
	delta = ktime_sub(now, last_jiffies_update);
	if (delta < tick_period)
		return;

	/* Reevaluate with jiffies_lock held */
	write_seqlock(&jiffies_lock);

	delta = ktime_sub(now, last_jiffies_update);
	if (delta >= tick_period) {

		delta = ktime_sub(delta, tick_period);
		last_jiffies_update = ktime_add(last_jiffies_update,
						tick_period);

		/* Slow path for long timeouts */
		if (unlikely(delta >= tick_period)) {
			s64 incr = ktime_to_ns(tick_period);

			ticks = ktime_divns(delta, incr);

			last_jiffies_update = ktime_add_ns(last_jiffies_update,
							   incr * ticks);
		}
		do_timer(++ticks);

		/* Keep the tick_next_period variable up to date */
		tick_next_period = ktime_add(last_jiffies_update, tick_period);
	} else {
		write_sequnlock(&jiffies_lock);
		return;
	}
	write_sequnlock(&jiffies_lock);
	update_wall_time();
}

/*
 * Initialize and return retrieve the jiffies update.
 */
static ktime_t tick_init_jiffy_update(void)
{
	ktime_t period;

	write_seqlock(&jiffies_lock);
	/* Did we start the jiffies update yet ? */
	if (last_jiffies_update == 0)
		last_jiffies_update = tick_next_period;
	period = last_jiffies_update;
	write_sequnlock(&jiffies_lock);
	return period;
}


static void tick_sched_do_timer(ktime_t now)
{
	int cpu = smp_processor_id();

#ifdef CONFIG_NO_HZ_COMMON
	/*
	 * Check if the do_timer duty was dropped. We don't care about
	 * concurrency: This happens only when the CPU in charge went
	 * into a long sleep. If two CPUs happen to assign themselves to
	 * this duty, then the jiffies update is still serialized by
	 * jiffies_lock.
	 */
	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
	    && !tick_nohz_full_cpu(cpu))
		tick_do_timer_cpu = cpu;
#endif

	/* Check, if the jiffies need an update */
	if (tick_do_timer_cpu == cpu)
		tick_do_update_jiffies64(now);
}

static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
{
#ifdef CONFIG_NO_HZ_COMMON
	/*
	 * When we are idle and the tick is stopped, we have to touch
	 * the watchdog as we might not schedule for a really long
	 * time. This happens on complete idle SMP systems while
	 * waiting on the login prompt. We also increment the "start of
	 * idle" jiffy stamp so the idle accounting adjustment we do
	 * when we go busy again does not account too much ticks.
	 */
	if (ts->tick_stopped) {
		touch_softlockup_watchdog_sched();
		if (is_idle_task(current))
			ts->idle_jiffies++;
	}
#endif
	update_process_times(user_mode(regs));
	profile_tick(CPU_PROFILING);
}
#endif

#ifdef CONFIG_NO_HZ_FULL
cpumask_var_t tick_nohz_full_mask;
cpumask_var_t housekeeping_mask;
bool tick_nohz_full_running;
static atomic_t tick_dep_mask;

static bool check_tick_dependency(atomic_t *dep)
{
	int val = atomic_read(dep);

	if (val & TICK_DEP_MASK_POSIX_TIMER) {
		trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
		return true;
	}

	if (val & TICK_DEP_MASK_PERF_EVENTS) {
		trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
		return true;
	}

	if (val & TICK_DEP_MASK_SCHED) {
		trace_tick_stop(0, TICK_DEP_MASK_SCHED);
		return true;
	}

	if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
		trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
		return true;
	}

	return false;
}

static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
{
	WARN_ON_ONCE(!irqs_disabled());

	if (unlikely(!cpu_online(cpu)))
		return false;

	if (check_tick_dependency(&tick_dep_mask))
		return false;

	if (check_tick_dependency(&ts->tick_dep_mask))
		return false;

	if (check_tick_dependency(&current->tick_dep_mask))
		return false;

	if (check_tick_dependency(&current->signal->tick_dep_mask))
		return false;

	return true;
}

static void nohz_full_kick_func(struct irq_work *work)
{
	/* Empty, the tick restart happens on tick_nohz_irq_exit() */
}

static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
	.func = nohz_full_kick_func,
};

/*
 * Kick this CPU if it's full dynticks in order to force it to
 * re-evaluate its dependency on the tick and restart it if necessary.
 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
 * is NMI safe.
 */
static void tick_nohz_full_kick(void)
{
	if (!tick_nohz_full_cpu(smp_processor_id()))
		return;

	irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
}

/*
 * Kick the CPU if it's full dynticks in order to force it to
 * re-evaluate its dependency on the tick and restart it if necessary.
 */
void tick_nohz_full_kick_cpu(int cpu)
{
	if (!tick_nohz_full_cpu(cpu))
		return;

	irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
}

/*
 * Kick all full dynticks CPUs in order to force these to re-evaluate
 * their dependency on the tick and restart it if necessary.
 */
static void tick_nohz_full_kick_all(void)
{
	int cpu;

	if (!tick_nohz_full_running)
		return;

	preempt_disable();
	for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
		tick_nohz_full_kick_cpu(cpu);
	preempt_enable();
}

static void tick_nohz_dep_set_all(atomic_t *dep,
				  enum tick_dep_bits bit)
{
	int prev;

	prev = atomic_fetch_or(BIT(bit), dep);
	if (!prev)
		tick_nohz_full_kick_all();
}

/*
 * Set a global tick dependency. Used by perf events that rely on freq and
 * by unstable clock.
 */
void tick_nohz_dep_set(enum tick_dep_bits bit)
{
	tick_nohz_dep_set_all(&tick_dep_mask, bit);
}

void tick_nohz_dep_clear(enum tick_dep_bits bit)
{
	atomic_andnot(BIT(bit), &tick_dep_mask);
}

/*
 * Set per-CPU tick dependency. Used by scheduler and perf events in order to
 * manage events throttling.
 */
void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
{
	int prev;
	struct tick_sched *ts;

	ts = per_cpu_ptr(&tick_cpu_sched, cpu);

	prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
	if (!prev) {
		preempt_disable();
		/* Perf needs local kick that is NMI safe */
		if (cpu == smp_processor_id()) {
			tick_nohz_full_kick();
		} else {
			/* Remote irq work not NMI-safe */
			if (!WARN_ON_ONCE(in_nmi()))
				tick_nohz_full_kick_cpu(cpu);
		}
		preempt_enable();
	}
}

void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
{
	struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);

	atomic_andnot(BIT(bit), &ts->tick_dep_mask);
}

/*
 * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
 * per task timers.
 */
void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
{
	/*
	 * We could optimize this with just kicking the target running the task
	 * if that noise matters for nohz full users.
	 */
	tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
}

void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
{
	atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
}

/*
 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
 * per process timers.
 */
void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
{
	tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
}

void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
{
	atomic_andnot(BIT(bit), &sig->tick_dep_mask);
}

/*
 * Re-evaluate the need for the tick as we switch the current task.
 * It might need the tick due to per task/process properties:
 * perf events, posix CPU timers, ...
 */
void __tick_nohz_task_switch(void)
{
	unsigned long flags;
	struct tick_sched *ts;

	local_irq_save(flags);

	if (!tick_nohz_full_cpu(smp_processor_id()))
		goto out;

	ts = this_cpu_ptr(&tick_cpu_sched);

	if (ts->tick_stopped) {
		if (atomic_read(&current->tick_dep_mask) ||
		    atomic_read(&current->signal->tick_dep_mask))
			tick_nohz_full_kick();
	}
out:
	local_irq_restore(flags);
}

/* Parse the boot-time nohz CPU list from the kernel parameters. */
static int __init tick_nohz_full_setup(char *str)
{
	alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
	if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
		pr_warn("NO_HZ: Incorrect nohz_full cpumask\n");
		free_bootmem_cpumask_var(tick_nohz_full_mask);
		return 1;
	}
	tick_nohz_full_running = true;

	return 1;
}
__setup("nohz_full=", tick_nohz_full_setup);

static int tick_nohz_cpu_down(unsigned int cpu)
{
	/*
	 * The boot CPU handles housekeeping duty (unbound timers,
	 * workqueues, timekeeping, ...) on behalf of full dynticks
	 * CPUs. It must remain online when nohz full is enabled.
	 */
	if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
		return -EBUSY;
	return 0;
}

static int tick_nohz_init_all(void)
{
	int err = -1;

#ifdef CONFIG_NO_HZ_FULL_ALL
	if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
		WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
		return err;
	}
	err = 0;
	cpumask_setall(tick_nohz_full_mask);
	tick_nohz_full_running = true;
#endif
	return err;
}

void __init tick_nohz_init(void)
{
	int cpu, ret;

	if (!tick_nohz_full_running) {
		if (tick_nohz_init_all() < 0)
			return;
	}

	if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
		WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
		cpumask_clear(tick_nohz_full_mask);
		tick_nohz_full_running = false;
		return;
	}

	/*
	 * Full dynticks uses irq work to drive the tick rescheduling on safe
	 * locking contexts. But then we need irq work to raise its own
	 * interrupts to avoid circular dependency on the tick
	 */
	if (!arch_irq_work_has_interrupt()) {
		pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
		cpumask_clear(tick_nohz_full_mask);
		cpumask_copy(housekeeping_mask, cpu_possible_mask);
		tick_nohz_full_running = false;
		return;
	}

	cpu = smp_processor_id();

	if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
		pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
			cpu);
		cpumask_clear_cpu(cpu, tick_nohz_full_mask);
	}

	cpumask_andnot(housekeeping_mask,
		       cpu_possible_mask, tick_nohz_full_mask);

	for_each_cpu(cpu, tick_nohz_full_mask)
		context_tracking_cpu_set(cpu);

	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
					"kernel/nohz:predown", NULL,
					tick_nohz_cpu_down);
	WARN_ON(ret < 0);
	pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
		cpumask_pr_args(tick_nohz_full_mask));

	/*
	 * We need at least one CPU to handle housekeeping work such
	 * as timekeeping, unbound timers, workqueues, ...
	 */
	WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
}
#endif

/*
 * NOHZ - aka dynamic tick functionality
 */
#ifdef CONFIG_NO_HZ_COMMON
/*
 * NO HZ enabled ?
 */
bool tick_nohz_enabled __read_mostly  = true;
unsigned long tick_nohz_active  __read_mostly;
/*
 * Enable / Disable tickless mode
 */
static int __init setup_tick_nohz(char *str)
{
	return (kstrtobool(str, &tick_nohz_enabled) == 0);
}

__setup("nohz=", setup_tick_nohz);

int tick_nohz_tick_stopped(void)
{
	return __this_cpu_read(tick_cpu_sched.tick_stopped);
}

/**
 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
 *
 * Called from interrupt entry when the CPU was idle
 *
 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
 * must be updated. Otherwise an interrupt handler could use a stale jiffy
 * value. We do this unconditionally on any CPU, as we don't know whether the
 * CPU, which has the update task assigned is in a long sleep.
 */
static void tick_nohz_update_jiffies(ktime_t now)
{
	unsigned long flags;

	__this_cpu_write(tick_cpu_sched.idle_waketime, now);

	local_irq_save(flags);
	tick_do_update_jiffies64(now);
	local_irq_restore(flags);

	touch_softlockup_watchdog_sched();
}

/*
 * Updates the per-CPU time idle statistics counters
 */
static void
update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
{
	ktime_t delta;

	if (ts->idle_active) {
		delta = ktime_sub(now, ts->idle_entrytime);
		if (nr_iowait_cpu(cpu) > 0)
			ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
		else
			ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
		ts->idle_entrytime = now;
	}

	if (last_update_time)
		*last_update_time = ktime_to_us(now);

}

static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
{
	update_ts_time_stats(smp_processor_id(), ts, now, NULL);
	ts->idle_active = 0;

	sched_clock_idle_wakeup_event(0);
}

static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
{
	ktime_t now = ktime_get();

	ts->idle_entrytime = now;
	ts->idle_active = 1;
	sched_clock_idle_sleep_event();
	return now;
}

/**
 * get_cpu_idle_time_us - get the total idle time of a CPU
 * @cpu: CPU number to query
 * @last_update_time: variable to store update time in. Do not update
 * counters if NULL.
 *
 * Return the cumulative idle time (since boot) for a given
 * CPU, in microseconds.
 *
 * This time is measured via accounting rather than sampling,
 * and is as accurate as ktime_get() is.
 *
 * This function returns -1 if NOHZ is not enabled.
 */
u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
{
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
	ktime_t now, idle;

	if (!tick_nohz_active)
		return -1;

	now = ktime_get();
	if (last_update_time) {
		update_ts_time_stats(cpu, ts, now, last_update_time);
		idle = ts->idle_sleeptime;
	} else {
		if (ts->idle_active && !nr_iowait_cpu(cpu)) {
			ktime_t delta = ktime_sub(now, ts->idle_entrytime);

			idle = ktime_add(ts->idle_sleeptime, delta);
		} else {
			idle = ts->idle_sleeptime;
		}
	}

	return ktime_to_us(idle);

}
EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);

/**
 * get_cpu_iowait_time_us - get the total iowait time of a CPU
 * @cpu: CPU number to query
 * @last_update_time: variable to store update time in. Do not update
 * counters if NULL.
 *
 * Return the cumulative iowait time (since boot) for a given
 * CPU, in microseconds.
 *
 * This time is measured via accounting rather than sampling,
 * and is as accurate as ktime_get() is.
 *
 * This function returns -1 if NOHZ is not enabled.
 */
u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
{
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
	ktime_t now, iowait;

	if (!tick_nohz_active)
		return -1;

	now = ktime_get();
	if (last_update_time) {
		update_ts_time_stats(cpu, ts, now, last_update_time);
		iowait = ts->iowait_sleeptime;
	} else {
		if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
			ktime_t delta = ktime_sub(now, ts->idle_entrytime);

			iowait = ktime_add(ts->iowait_sleeptime, delta);
		} else {
			iowait = ts->iowait_sleeptime;
		}
	}

	return ktime_to_us(iowait);
}
EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);

static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
{
	hrtimer_cancel(&ts->sched_timer);
	hrtimer_set_expires(&ts->sched_timer, ts->last_tick);

	/* Forward the time to expire in the future */
	hrtimer_forward(&ts->sched_timer, now, tick_period);

	if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
		hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
	else
		tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
}

static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
					 ktime_t now, int cpu)
{
	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
	u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
	unsigned long seq, basejiff;
	ktime_t	tick;

	/* Read jiffies and the time when jiffies were updated last */
	do {
		seq = read_seqbegin(&jiffies_lock);
		basemono = last_jiffies_update;
		basejiff = jiffies;
	} while (read_seqretry(&jiffies_lock, seq));
	ts->last_jiffies = basejiff;

	if (rcu_needs_cpu(basemono, &next_rcu) ||
	    arch_needs_cpu() || irq_work_needs_cpu()) {
		next_tick = basemono + TICK_NSEC;
	} else {
		/*
		 * Get the next pending timer. If high resolution
		 * timers are enabled this only takes the timer wheel
		 * timers into account. If high resolution timers are
		 * disabled this also looks at the next expiring
		 * hrtimer.
		 */
		next_tmr = get_next_timer_interrupt(basejiff, basemono);
		ts->next_timer = next_tmr;
		/* Take the next rcu event into account */
		next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
	}

	/*
	 * If the tick is due in the next period, keep it ticking or
	 * force prod the timer.
	 */
	delta = next_tick - basemono;
	if (delta <= (u64)TICK_NSEC) {
		tick = 0;

		/*
		 * Tell the timer code that the base is not idle, i.e. undo
		 * the effect of get_next_timer_interrupt():
		 */
		timer_clear_idle();
		/*
		 * We've not stopped the tick yet, and there's a timer in the
		 * next period, so no point in stopping it either, bail.
		 */
		if (!ts->tick_stopped)
			goto out;

		/*
		 * If, OTOH, we did stop it, but there's a pending (expired)
		 * timer reprogram the timer hardware to fire now.
		 *
		 * We will not restart the tick proper, just prod the timer
		 * hardware into firing an interrupt to process the pending
		 * timers. Just like tick_irq_exit() will not restart the tick
		 * for 'normal' interrupts.
		 *
		 * Only once we exit the idle loop will we re-enable the tick,
		 * see tick_nohz_idle_exit().
		 */
		if (delta == 0) {
			tick_nohz_restart(ts, now);
			goto out;
		}
	}

	/*
	 * If this CPU is the one which updates jiffies, then give up
	 * the assignment and let it be taken by the CPU which runs
	 * the tick timer next, which might be this CPU as well. If we
	 * don't drop this here the jiffies might be stale and
	 * do_timer() never invoked. Keep track of the fact that it
	 * was the one which had the do_timer() duty last. If this CPU
	 * is the one which had the do_timer() duty last, we limit the
	 * sleep time to the timekeeping max_deferment value.
	 * Otherwise we can sleep as long as we want.
	 */
	delta = timekeeping_max_deferment();
	if (cpu == tick_do_timer_cpu) {
		tick_do_timer_cpu = TICK_DO_TIMER_NONE;
		ts->do_timer_last = 1;
	} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
		delta = KTIME_MAX;
		ts->do_timer_last = 0;
	} else if (!ts->do_timer_last) {
		delta = KTIME_MAX;
	}

#ifdef CONFIG_NO_HZ_FULL
	/* Limit the tick delta to the maximum scheduler deferment */
	if (!ts->inidle)
		delta = min(delta, scheduler_tick_max_deferment());
#endif

	/* Calculate the next expiry time */
	if (delta < (KTIME_MAX - basemono))
		expires = basemono + delta;
	else
		expires = KTIME_MAX;

	expires = min_t(u64, expires, next_tick);
	tick = expires;

	/* Skip reprogram of event if its not changed */
	if (ts->tick_stopped && (expires == dev->next_event))
		goto out;

	/*
	 * nohz_stop_sched_tick can be called several times before
	 * the nohz_restart_sched_tick is called. This happens when
	 * interrupts arrive which do not cause a reschedule. In the
	 * first call we save the current tick time, so we can restart
	 * the scheduler tick in nohz_restart_sched_tick.
	 */
	if (!ts->tick_stopped) {
		nohz_balance_enter_idle(cpu);
		calc_load_enter_idle();
		cpu_load_update_nohz_start();

		ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
		ts->tick_stopped = 1;
		trace_tick_stop(1, TICK_DEP_MASK_NONE);
	}

	/*
	 * If the expiration time == KTIME_MAX, then we simply stop
	 * the tick timer.
	 */
	if (unlikely(expires == KTIME_MAX)) {
		if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
			hrtimer_cancel(&ts->sched_timer);
		goto out;
	}

	if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
		hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
	else
		tick_program_event(tick, 1);
out:
	/* Update the estimated sleep length */
	ts->sleep_length = ktime_sub(dev->next_event, now);
	return tick;
}

static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
{
	/* Update jiffies first */
	tick_do_update_jiffies64(now);
	cpu_load_update_nohz_stop();

	/*
	 * Clear the timer idle flag, so we avoid IPIs on remote queueing and
	 * the clock forward checks in the enqueue path:
	 */
	timer_clear_idle();

	calc_load_exit_idle();
	touch_softlockup_watchdog_sched();
	/*
	 * Cancel the scheduled timer and restore the tick
	 */
	ts->tick_stopped  = 0;
	ts->idle_exittime = now;

	tick_nohz_restart(ts, now);
}

static void tick_nohz_full_update_tick(struct tick_sched *ts)
{
#ifdef CONFIG_NO_HZ_FULL
	int cpu = smp_processor_id();

	if (!tick_nohz_full_cpu(cpu))
		return;

	if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
		return;

	if (can_stop_full_tick(cpu, ts))
		tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
	else if (ts->tick_stopped)
		tick_nohz_restart_sched_tick(ts, ktime_get());
#endif
}

static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
{
	/*
	 * If this CPU is offline and it is the one which updates
	 * jiffies, then give up the assignment and let it be taken by
	 * the CPU which runs the tick timer next. If we don't drop
	 * this here the jiffies might be stale and do_timer() never
	 * invoked.
	 */
	if (unlikely(!cpu_online(cpu))) {
		if (cpu == tick_do_timer_cpu)
			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
		return false;
	}

	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
		ts->sleep_length = NSEC_PER_SEC / HZ;
		return false;
	}

	if (need_resched())
		return false;

	if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
		static int ratelimit;

		if (ratelimit < 10 &&
		    (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
			pr_warn("NOHZ: local_softirq_pending %02x\n",
				(unsigned int) local_softirq_pending());
			ratelimit++;
		}
		return false;
	}

	if (tick_nohz_full_enabled()) {
		/*
		 * Keep the tick alive to guarantee timekeeping progression
		 * if there are full dynticks CPUs around
		 */
		if (tick_do_timer_cpu == cpu)
			return false;
		/*
		 * Boot safety: make sure the timekeeping duty has been
		 * assigned before entering dyntick-idle mode,
		 */
		if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
			return false;
	}

	return true;
}

static void __tick_nohz_idle_enter(struct tick_sched *ts)
{
	ktime_t now, expires;
	int cpu = smp_processor_id();

	now = tick_nohz_start_idle(ts);

	if (can_stop_idle_tick(cpu, ts)) {
		int was_stopped = ts->tick_stopped;

		ts->idle_calls++;

		expires = tick_nohz_stop_sched_tick(ts, now, cpu);
		if (expires > 0LL) {
			ts->idle_sleeps++;
			ts->idle_expires = expires;
		}

		if (!was_stopped && ts->tick_stopped)
			ts->idle_jiffies = ts->last_jiffies;
	}
}

/**
 * tick_nohz_idle_enter - stop the idle tick from the idle task
 *
 * When the next event is more than a tick into the future, stop the idle tick
 * Called when we start the idle loop.
 *
 * The arch is responsible of calling:
 *
 * - rcu_idle_enter() after its last use of RCU before the CPU is put
 *  to sleep.
 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
 */
void tick_nohz_idle_enter(void)
{
	struct tick_sched *ts;

	WARN_ON_ONCE(irqs_disabled());

	/*
	 * Update the idle state in the scheduler domain hierarchy
	 * when tick_nohz_stop_sched_tick() is called from the idle loop.
	 * State will be updated to busy during the first busy tick after
	 * exiting idle.
	 */
	set_cpu_sd_state_idle();

	local_irq_disable();

	ts = this_cpu_ptr(&tick_cpu_sched);
	ts->inidle = 1;
	__tick_nohz_idle_enter(ts);

	local_irq_enable();
}

/**
 * tick_nohz_irq_exit - update next tick event from interrupt exit
 *
 * When an interrupt fires while we are idle and it doesn't cause
 * a reschedule, it may still add, modify or delete a timer, enqueue
 * an RCU callback, etc...
 * So we need to re-calculate and reprogram the next tick event.
 */
void tick_nohz_irq_exit(void)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

	if (ts->inidle)
		__tick_nohz_idle_enter(ts);
	else
		tick_nohz_full_update_tick(ts);
}

/**
 * tick_nohz_get_sleep_length - return the length of the current sleep
 *
 * Called from power state control code with interrupts disabled
 */
ktime_t tick_nohz_get_sleep_length(void)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

	return ts->sleep_length;
}

static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
{
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
	unsigned long ticks;

	if (vtime_accounting_cpu_enabled())
		return;
	/*
	 * We stopped the tick in idle. Update process times would miss the
	 * time we slept as update_process_times does only a 1 tick
	 * accounting. Enforce that this is accounted to idle !
	 */
	ticks = jiffies - ts->idle_jiffies;
	/*
	 * We might be one off. Do not randomly account a huge number of ticks!
	 */
	if (ticks && ticks < LONG_MAX)
		account_idle_ticks(ticks);
#endif
}

/**
 * tick_nohz_idle_exit - restart the idle tick from the idle task
 *
 * Restart the idle tick when the CPU is woken up from idle
 * This also exit the RCU extended quiescent state. The CPU
 * can use RCU again after this function is called.
 */
void tick_nohz_idle_exit(void)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
	ktime_t now;

	local_irq_disable();

	WARN_ON_ONCE(!ts->inidle);

	ts->inidle = 0;

	if (ts->idle_active || ts->tick_stopped)
		now = ktime_get();

	if (ts->idle_active)
		tick_nohz_stop_idle(ts, now);

	if (ts->tick_stopped) {
		tick_nohz_restart_sched_tick(ts, now);
		tick_nohz_account_idle_ticks(ts);
	}

	local_irq_enable();
}

/*
 * The nohz low res interrupt handler
 */
static void tick_nohz_handler(struct clock_event_device *dev)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
	struct pt_regs *regs = get_irq_regs();
	ktime_t now = ktime_get();

	dev->next_event = KTIME_MAX;

	tick_sched_do_timer(now);
	tick_sched_handle(ts, regs);

	/* No need to reprogram if we are running tickless  */
	if (unlikely(ts->tick_stopped))
		return;

	hrtimer_forward(&ts->sched_timer, now, tick_period);
	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
}

static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
{
	if (!tick_nohz_enabled)
		return;
	ts->nohz_mode = mode;
	/* One update is enough */
	if (!test_and_set_bit(0, &tick_nohz_active))
		timers_update_migration(true);
}

/**
 * tick_nohz_switch_to_nohz - switch to nohz mode
 */
static void tick_nohz_switch_to_nohz(void)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
	ktime_t next;

	if (!tick_nohz_enabled)
		return;

	if (tick_switch_to_oneshot(tick_nohz_handler))
		return;

	/*
	 * Recycle the hrtimer in ts, so we can share the
	 * hrtimer_forward with the highres code.
	 */
	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	/* Get the next period */
	next = tick_init_jiffy_update();

	hrtimer_set_expires(&ts->sched_timer, next);
	hrtimer_forward_now(&ts->sched_timer, tick_period);
	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
}

static inline void tick_nohz_irq_enter(void)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
	ktime_t now;

	if (!ts->idle_active && !ts->tick_stopped)
		return;
	now = ktime_get();
	if (ts->idle_active)
		tick_nohz_stop_idle(ts, now);
	if (ts->tick_stopped)
		tick_nohz_update_jiffies(now);
}

#else

static inline void tick_nohz_switch_to_nohz(void) { }
static inline void tick_nohz_irq_enter(void) { }
static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }

#endif /* CONFIG_NO_HZ_COMMON */

/*
 * Called from irq_enter to notify about the possible interruption of idle()
 */
void tick_irq_enter(void)
{
	tick_check_oneshot_broadcast_this_cpu();
	tick_nohz_irq_enter();
}

/*
 * High resolution timer specific code
 */
#ifdef CONFIG_HIGH_RES_TIMERS
/*
 * We rearm the timer until we get disabled by the idle code.
 * Called with interrupts disabled.
 */
static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
{
	struct tick_sched *ts =
		container_of(timer, struct tick_sched, sched_timer);
	struct pt_regs *regs = get_irq_regs();
	ktime_t now = ktime_get();

	tick_sched_do_timer(now);

	/*
	 * Do not call, when we are not in irq context and have
	 * no valid regs pointer
	 */
	if (regs)
		tick_sched_handle(ts, regs);

	/* No need to reprogram if we are in idle or full dynticks mode */
	if (unlikely(ts->tick_stopped))
		return HRTIMER_NORESTART;

	hrtimer_forward(timer, now, tick_period);

	return HRTIMER_RESTART;
}

static int sched_skew_tick;

static int __init skew_tick(char *str)
{
	get_option(&str, &sched_skew_tick);

	return 0;
}
early_param("skew_tick", skew_tick);

/**
 * tick_setup_sched_timer - setup the tick emulation timer
 */
void tick_setup_sched_timer(void)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
	ktime_t now = ktime_get();

	/*
	 * Emulate tick processing via per-CPU hrtimers:
	 */
	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	ts->sched_timer.function = tick_sched_timer;

	/* Get the next period (per-CPU) */
	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());

	/* Offset the tick to avert jiffies_lock contention. */
	if (sched_skew_tick) {
		u64 offset = ktime_to_ns(tick_period) >> 1;
		do_div(offset, num_possible_cpus());
		offset *= smp_processor_id();
		hrtimer_add_expires_ns(&ts->sched_timer, offset);
	}

	hrtimer_forward(&ts->sched_timer, now, tick_period);
	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
}
#endif /* HIGH_RES_TIMERS */

#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
void tick_cancel_sched_timer(int cpu)
{
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

# ifdef CONFIG_HIGH_RES_TIMERS
	if (ts->sched_timer.base)
		hrtimer_cancel(&ts->sched_timer);
# endif

	memset(ts, 0, sizeof(*ts));
}
#endif

/**
 * Async notification about clocksource changes
 */
void tick_clock_notify(void)
{
	int cpu;

	for_each_possible_cpu(cpu)
		set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
}

/*
 * Async notification about clock event changes
 */
void tick_oneshot_notify(void)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

	set_bit(0, &ts->check_clocks);
}

/**
 * Check, if a change happened, which makes oneshot possible.
 *
 * Called cyclic from the hrtimer softirq (driven by the timer
 * softirq) allow_nohz signals, that we can switch into low-res nohz
 * mode, because high resolution timers are disabled (either compile
 * or runtime). Called with interrupts disabled.
 */
int tick_check_oneshot_change(int allow_nohz)
{
	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

	if (!test_and_clear_bit(0, &ts->check_clocks))
		return 0;

	if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
		return 0;

	if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
		return 0;

	if (!allow_nohz)
		return 1;

	tick_nohz_switch_to_nohz();
	return 0;
}