summaryrefslogtreecommitdiff
path: root/kernel/sched/cputime.c
blob: 2ee83b2005043725a2771bb3cb861b92b7a03250 (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
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/tsacct_kern.h>
#include <linux/kernel_stat.h>
#include <linux/static_key.h>
#include <linux/context_tracking.h>
#include "sched.h"
#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
#endif


#ifdef CONFIG_IRQ_TIME_ACCOUNTING

/*
 * There are no locks covering percpu hardirq/softirq time.
 * They are only modified in vtime_account, on corresponding CPU
 * with interrupts disabled. So, writes are safe.
 * They are read and saved off onto struct rq in update_rq_clock().
 * This may result in other CPU reading this CPU's irq time and can
 * race with irq/vtime_account on this CPU. We would either get old
 * or new value with a side effect of accounting a slice of irq time to wrong
 * task when irq is in progress while we read rq->clock. That is a worthy
 * compromise in place of having locks on each irq in account_system_time.
 */
DEFINE_PER_CPU(u64, cpu_hardirq_time);
DEFINE_PER_CPU(u64, cpu_softirq_time);

static DEFINE_PER_CPU(u64, irq_start_time);
static int sched_clock_irqtime;

void enable_sched_clock_irqtime(void)
{
	sched_clock_irqtime = 1;
}

void disable_sched_clock_irqtime(void)
{
	sched_clock_irqtime = 0;
}

#ifndef CONFIG_64BIT
DEFINE_PER_CPU(seqcount_t, irq_time_seq);
#endif /* CONFIG_64BIT */

/*
 * Called before incrementing preempt_count on {soft,}irq_enter
 * and before decrementing preempt_count on {soft,}irq_exit.
 */
void irqtime_account_irq(struct task_struct *curr)
{
	s64 delta;
	int cpu;

	if (!sched_clock_irqtime)
		return;

	cpu = smp_processor_id();
	delta = sched_clock_cpu(cpu) - __this_cpu_read(irq_start_time);
	__this_cpu_add(irq_start_time, delta);

	irq_time_write_begin();
	/*
	 * We do not account for softirq time from ksoftirqd here.
	 * We want to continue accounting softirq time to ksoftirqd thread
	 * in that case, so as not to confuse scheduler with a special task
	 * that do not consume any time, but still wants to run.
	 */
	if (hardirq_count())
		__this_cpu_add(cpu_hardirq_time, delta);
	else if (in_serving_softirq() && curr != this_cpu_ksoftirqd())
		__this_cpu_add(cpu_softirq_time, delta);

	irq_time_write_end();
}
EXPORT_SYMBOL_GPL(irqtime_account_irq);

static cputime_t irqtime_account_hi_update(cputime_t maxtime)
{
	u64 *cpustat = kcpustat_this_cpu->cpustat;
	unsigned long flags;
	cputime_t irq_cputime;

	local_irq_save(flags);
	irq_cputime = nsecs_to_cputime64(this_cpu_read(cpu_hardirq_time)) -
		      cpustat[CPUTIME_IRQ];
	irq_cputime = min(irq_cputime, maxtime);
	cpustat[CPUTIME_IRQ] += irq_cputime;
	local_irq_restore(flags);
	return irq_cputime;
}

static cputime_t irqtime_account_si_update(cputime_t maxtime)
{
	u64 *cpustat = kcpustat_this_cpu->cpustat;
	unsigned long flags;
	cputime_t softirq_cputime;

	local_irq_save(flags);
	softirq_cputime = nsecs_to_cputime64(this_cpu_read(cpu_softirq_time)) -
			  cpustat[CPUTIME_SOFTIRQ];
	softirq_cputime = min(softirq_cputime, maxtime);
	cpustat[CPUTIME_SOFTIRQ] += softirq_cputime;
	local_irq_restore(flags);
	return softirq_cputime;
}

#else /* CONFIG_IRQ_TIME_ACCOUNTING */

#define sched_clock_irqtime	(0)

static cputime_t irqtime_account_hi_update(cputime_t dummy)
{
	return 0;
}

static cputime_t irqtime_account_si_update(cputime_t dummy)
{
	return 0;
}

#endif /* !CONFIG_IRQ_TIME_ACCOUNTING */

static inline void task_group_account_field(struct task_struct *p, int index,
					    u64 tmp)
{
	/*
	 * Since all updates are sure to touch the root cgroup, we
	 * get ourselves ahead and touch it first. If the root cgroup
	 * is the only cgroup, then nothing else should be necessary.
	 *
	 */
	__this_cpu_add(kernel_cpustat.cpustat[index], tmp);

	cpuacct_account_field(p, index, tmp);
}

/*
 * Account user cpu time to a process.
 * @p: the process that the cpu time gets accounted to
 * @cputime: the cpu time spent in user space since the last update
 * @cputime_scaled: cputime scaled by cpu frequency
 */
void account_user_time(struct task_struct *p, cputime_t cputime,
		       cputime_t cputime_scaled)
{
	int index;

	/* Add user time to process. */
	p->utime += cputime;
	p->utimescaled += cputime_scaled;
	account_group_user_time(p, cputime);

	index = (task_nice(p) > 0) ? CPUTIME_NICE : CPUTIME_USER;

	/* Add user time to cpustat. */
	task_group_account_field(p, index, (__force u64) cputime);

	/* Account for user time used */
	acct_account_cputime(p);
}

/*
 * Account guest cpu time to a process.
 * @p: the process that the cpu time gets accounted to
 * @cputime: the cpu time spent in virtual machine since the last update
 * @cputime_scaled: cputime scaled by cpu frequency
 */
static void account_guest_time(struct task_struct *p, cputime_t cputime,
			       cputime_t cputime_scaled)
{
	u64 *cpustat = kcpustat_this_cpu->cpustat;

	/* Add guest time to process. */
	p->utime += cputime;
	p->utimescaled += cputime_scaled;
	account_group_user_time(p, cputime);
	p->gtime += cputime;

	/* Add guest time to cpustat. */
	if (task_nice(p) > 0) {
		cpustat[CPUTIME_NICE] += (__force u64) cputime;
		cpustat[CPUTIME_GUEST_NICE] += (__force u64) cputime;
	} else {
		cpustat[CPUTIME_USER] += (__force u64) cputime;
		cpustat[CPUTIME_GUEST] += (__force u64) cputime;
	}
}

/*
 * Account system cpu time to a process and desired cpustat field
 * @p: the process that the cpu time gets accounted to
 * @cputime: the cpu time spent in kernel space since the last update
 * @cputime_scaled: cputime scaled by cpu frequency
 * @target_cputime64: pointer to cpustat field that has to be updated
 */
static inline
void __account_system_time(struct task_struct *p, cputime_t cputime,
			cputime_t cputime_scaled, int index)
{
	/* Add system time to process. */
	p->stime += cputime;
	p->stimescaled += cputime_scaled;
	account_group_system_time(p, cputime);

	/* Add system time to cpustat. */
	task_group_account_field(p, index, (__force u64) cputime);

	/* Account for system time used */
	acct_account_cputime(p);
}

/*
 * Account system cpu time to a process.
 * @p: the process that the cpu time gets accounted to
 * @hardirq_offset: the offset to subtract from hardirq_count()
 * @cputime: the cpu time spent in kernel space since the last update
 * @cputime_scaled: cputime scaled by cpu frequency
 */
void account_system_time(struct task_struct *p, int hardirq_offset,
			 cputime_t cputime, cputime_t cputime_scaled)
{
	int index;

	if ((p->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) {
		account_guest_time(p, cputime, cputime_scaled);
		return;
	}

	if (hardirq_count() - hardirq_offset)
		index = CPUTIME_IRQ;
	else if (in_serving_softirq())
		index = CPUTIME_SOFTIRQ;
	else
		index = CPUTIME_SYSTEM;

	__account_system_time(p, cputime, cputime_scaled, index);
}

/*
 * Account for involuntary wait time.
 * @cputime: the cpu time spent in involuntary wait
 */
void account_steal_time(cputime_t cputime)
{
	u64 *cpustat = kcpustat_this_cpu->cpustat;

	cpustat[CPUTIME_STEAL] += (__force u64) cputime;
}

/*
 * Account for idle time.
 * @cputime: the cpu time spent in idle wait
 */
void account_idle_time(cputime_t cputime)
{
	u64 *cpustat = kcpustat_this_cpu->cpustat;
	struct rq *rq = this_rq();

	if (atomic_read(&rq->nr_iowait) > 0)
		cpustat[CPUTIME_IOWAIT] += (__force u64) cputime;
	else
		cpustat[CPUTIME_IDLE] += (__force u64) cputime;
}

static __always_inline cputime_t steal_account_process_time(cputime_t maxtime)
{
#ifdef CONFIG_PARAVIRT
	if (static_key_false(&paravirt_steal_enabled)) {
		cputime_t steal_cputime;
		u64 steal;

		steal = paravirt_steal_clock(smp_processor_id());
		steal -= this_rq()->prev_steal_time;

		steal_cputime = min(nsecs_to_cputime(steal), maxtime);
		account_steal_time(steal_cputime);
		this_rq()->prev_steal_time += cputime_to_nsecs(steal_cputime);

		return steal_cputime;
	}
#endif
	return 0;
}

/*
 * Account how much elapsed time was spent in steal, irq, or softirq time.
 */
static inline cputime_t account_other_time(cputime_t max)
{
	cputime_t accounted;

	accounted = steal_account_process_time(max);

	if (accounted < max)
		accounted += irqtime_account_hi_update(max - accounted);

	if (accounted < max)
		accounted += irqtime_account_si_update(max - accounted);

	return accounted;
}

/*
 * Accumulate raw cputime values of dead tasks (sig->[us]time) and live
 * tasks (sum on group iteration) belonging to @tsk's group.
 */
void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
{
	struct signal_struct *sig = tsk->signal;
	cputime_t utime, stime;
	struct task_struct *t;
	unsigned int seq, nextseq;
	unsigned long flags;

	rcu_read_lock();
	/* Attempt a lockless read on the first round. */
	nextseq = 0;
	do {
		seq = nextseq;
		flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
		times->utime = sig->utime;
		times->stime = sig->stime;
		times->sum_exec_runtime = sig->sum_sched_runtime;

		for_each_thread(tsk, t) {
			task_cputime(t, &utime, &stime);
			times->utime += utime;
			times->stime += stime;
			times->sum_exec_runtime += task_sched_runtime(t);
		}
		/* If lockless access failed, take the lock. */
		nextseq = 1;
	} while (need_seqretry(&sig->stats_lock, seq));
	done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
	rcu_read_unlock();
}

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
/*
 * Account a tick to a process and cpustat
 * @p: the process that the cpu time gets accounted to
 * @user_tick: is the tick from userspace
 * @rq: the pointer to rq
 *
 * Tick demultiplexing follows the order
 * - pending hardirq update
 * - pending softirq update
 * - user_time
 * - idle_time
 * - system time
 *   - check for guest_time
 *   - else account as system_time
 *
 * Check for hardirq is done both for system and user time as there is
 * no timer going off while we are on hardirq and hence we may never get an
 * opportunity to update it solely in system time.
 * p->stime and friends are only updated on system time and not on irq
 * softirq as those do not count in task exec_runtime any more.
 */
static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
					 struct rq *rq, int ticks)
{
	u64 cputime = (__force u64) cputime_one_jiffy * ticks;
	cputime_t scaled, other;

	/*
	 * When returning from idle, many ticks can get accounted at
	 * once, including some ticks of steal, irq, and softirq time.
	 * Subtract those ticks from the amount of time accounted to
	 * idle, or potentially user or system time. Due to rounding,
	 * other time can exceed ticks occasionally.
	 */
	other = account_other_time(cputime);
	if (other >= cputime)
		return;
	cputime -= other;
	scaled = cputime_to_scaled(cputime);

	if (this_cpu_ksoftirqd() == p) {
		/*
		 * ksoftirqd time do not get accounted in cpu_softirq_time.
		 * So, we have to handle it separately here.
		 * Also, p->stime needs to be updated for ksoftirqd.
		 */
		__account_system_time(p, cputime, scaled, CPUTIME_SOFTIRQ);
	} else if (user_tick) {
		account_user_time(p, cputime, scaled);
	} else if (p == rq->idle) {
		account_idle_time(cputime);
	} else if (p->flags & PF_VCPU) { /* System time or guest time */
		account_guest_time(p, cputime, scaled);
	} else {
		__account_system_time(p, cputime, scaled,	CPUTIME_SYSTEM);
	}
}

static void irqtime_account_idle_ticks(int ticks)
{
	struct rq *rq = this_rq();

	irqtime_account_process_tick(current, 0, rq, ticks);
}
#else /* CONFIG_IRQ_TIME_ACCOUNTING */
static inline void irqtime_account_idle_ticks(int ticks) {}
static inline void irqtime_account_process_tick(struct task_struct *p, int user_tick,
						struct rq *rq, int nr_ticks) {}
#endif /* CONFIG_IRQ_TIME_ACCOUNTING */

/*
 * Use precise platform statistics if available:
 */
#ifdef CONFIG_VIRT_CPU_ACCOUNTING

#ifndef __ARCH_HAS_VTIME_TASK_SWITCH
void vtime_common_task_switch(struct task_struct *prev)
{
	if (is_idle_task(prev))
		vtime_account_idle(prev);
	else
		vtime_account_system(prev);

#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
	vtime_account_user(prev);
#endif
	arch_vtime_task_switch(prev);
}
#endif

#endif /* CONFIG_VIRT_CPU_ACCOUNTING */


#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
/*
 * Archs that account the whole time spent in the idle task
 * (outside irq) as idle time can rely on this and just implement
 * vtime_account_system() and vtime_account_idle(). Archs that
 * have other meaning of the idle time (s390 only includes the
 * time spent by the CPU when it's in low power mode) must override
 * vtime_account().
 */
#ifndef __ARCH_HAS_VTIME_ACCOUNT
void vtime_account_irq_enter(struct task_struct *tsk)
{
	if (!in_interrupt() && is_idle_task(tsk))
		vtime_account_idle(tsk);
	else
		vtime_account_system(tsk);
}
EXPORT_SYMBOL_GPL(vtime_account_irq_enter);
#endif /* __ARCH_HAS_VTIME_ACCOUNT */

void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
	*ut = p->utime;
	*st = p->stime;
}
EXPORT_SYMBOL_GPL(task_cputime_adjusted);

void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
	struct task_cputime cputime;

	thread_group_cputime(p, &cputime);

	*ut = cputime.utime;
	*st = cputime.stime;
}
#else /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
/*
 * Account a single tick of cpu time.
 * @p: the process that the cpu time gets accounted to
 * @user_tick: indicates if the tick is a user or a system tick
 */
void account_process_tick(struct task_struct *p, int user_tick)
{
	cputime_t cputime, scaled, steal;
	struct rq *rq = this_rq();

	if (vtime_accounting_cpu_enabled())
		return;

	if (sched_clock_irqtime) {
		irqtime_account_process_tick(p, user_tick, rq, 1);
		return;
	}

	cputime = cputime_one_jiffy;
	steal = steal_account_process_time(cputime);

	if (steal >= cputime)
		return;

	cputime -= steal;
	scaled = cputime_to_scaled(cputime);

	if (user_tick)
		account_user_time(p, cputime, scaled);
	else if ((p != rq->idle) || (irq_count() != HARDIRQ_OFFSET))
		account_system_time(p, HARDIRQ_OFFSET, cputime, scaled);
	else
		account_idle_time(cputime);
}

/*
 * Account multiple ticks of idle time.
 * @ticks: number of stolen ticks
 */
void account_idle_ticks(unsigned long ticks)
{
	cputime_t cputime, steal;

	if (sched_clock_irqtime) {
		irqtime_account_idle_ticks(ticks);
		return;
	}

	cputime = jiffies_to_cputime(ticks);
	steal = steal_account_process_time(cputime);

	if (steal >= cputime)
		return;

	cputime -= steal;
	account_idle_time(cputime);
}

/*
 * Perform (stime * rtime) / total, but avoid multiplication overflow by
 * loosing precision when the numbers are big.
 */
static cputime_t scale_stime(u64 stime, u64 rtime, u64 total)
{
	u64 scaled;

	for (;;) {
		/* Make sure "rtime" is the bigger of stime/rtime */
		if (stime > rtime)
			swap(rtime, stime);

		/* Make sure 'total' fits in 32 bits */
		if (total >> 32)
			goto drop_precision;

		/* Does rtime (and thus stime) fit in 32 bits? */
		if (!(rtime >> 32))
			break;

		/* Can we just balance rtime/stime rather than dropping bits? */
		if (stime >> 31)
			goto drop_precision;

		/* We can grow stime and shrink rtime and try to make them both fit */
		stime <<= 1;
		rtime >>= 1;
		continue;

drop_precision:
		/* We drop from rtime, it has more bits than stime */
		rtime >>= 1;
		total >>= 1;
	}

	/*
	 * Make sure gcc understands that this is a 32x32->64 multiply,
	 * followed by a 64/32->64 divide.
	 */
	scaled = div_u64((u64) (u32) stime * (u64) (u32) rtime, (u32)total);
	return (__force cputime_t) scaled;
}

/*
 * Adjust tick based cputime random precision against scheduler runtime
 * accounting.
 *
 * Tick based cputime accounting depend on random scheduling timeslices of a
 * task to be interrupted or not by the timer.  Depending on these
 * circumstances, the number of these interrupts may be over or
 * under-optimistic, matching the real user and system cputime with a variable
 * precision.
 *
 * Fix this by scaling these tick based values against the total runtime
 * accounted by the CFS scheduler.
 *
 * This code provides the following guarantees:
 *
 *   stime + utime == rtime
 *   stime_i+1 >= stime_i, utime_i+1 >= utime_i
 *
 * Assuming that rtime_i+1 >= rtime_i.
 */
static void cputime_adjust(struct task_cputime *curr,
			   struct prev_cputime *prev,
			   cputime_t *ut, cputime_t *st)
{
	cputime_t rtime, stime, utime;
	unsigned long flags;

	/* Serialize concurrent callers such that we can honour our guarantees */
	raw_spin_lock_irqsave(&prev->lock, flags);
	rtime = nsecs_to_cputime(curr->sum_exec_runtime);

	/*
	 * This is possible under two circumstances:
	 *  - rtime isn't monotonic after all (a bug);
	 *  - we got reordered by the lock.
	 *
	 * In both cases this acts as a filter such that the rest of the code
	 * can assume it is monotonic regardless of anything else.
	 */
	if (prev->stime + prev->utime >= rtime)
		goto out;

	stime = curr->stime;
	utime = curr->utime;

	/*
	 * If either stime or both stime and utime are 0, assume all runtime is
	 * userspace. Once a task gets some ticks, the monotonicy code at
	 * 'update' will ensure things converge to the observed ratio.
	 */
	if (stime == 0) {
		utime = rtime;
		goto update;
	}

	if (utime == 0) {
		stime = rtime;
		goto update;
	}

	stime = scale_stime((__force u64)stime, (__force u64)rtime,
			    (__force u64)(stime + utime));

update:
	/*
	 * Make sure stime doesn't go backwards; this preserves monotonicity
	 * for utime because rtime is monotonic.
	 *
	 *  utime_i+1 = rtime_i+1 - stime_i
	 *            = rtime_i+1 - (rtime_i - utime_i)
	 *            = (rtime_i+1 - rtime_i) + utime_i
	 *            >= utime_i
	 */
	if (stime < prev->stime)
		stime = prev->stime;
	utime = rtime - stime;

	/*
	 * Make sure utime doesn't go backwards; this still preserves
	 * monotonicity for stime, analogous argument to above.
	 */
	if (utime < prev->utime) {
		utime = prev->utime;
		stime = rtime - utime;
	}

	prev->stime = stime;
	prev->utime = utime;
out:
	*ut = prev->utime;
	*st = prev->stime;
	raw_spin_unlock_irqrestore(&prev->lock, flags);
}

void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
	struct task_cputime cputime = {
		.sum_exec_runtime = p->se.sum_exec_runtime,
	};

	task_cputime(p, &cputime.utime, &cputime.stime);
	cputime_adjust(&cputime, &p->prev_cputime, ut, st);
}
EXPORT_SYMBOL_GPL(task_cputime_adjusted);

void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
	struct task_cputime cputime;

	thread_group_cputime(p, &cputime);
	cputime_adjust(&cputime, &p->signal->prev_cputime, ut, st);
}
#endif /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */

#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
static cputime_t vtime_delta(struct task_struct *tsk)
{
	unsigned long now = READ_ONCE(jiffies);

	if (time_before(now, (unsigned long)tsk->vtime_snap))
		return 0;

	return jiffies_to_cputime(now - tsk->vtime_snap);
}

static cputime_t get_vtime_delta(struct task_struct *tsk)
{
	unsigned long now = READ_ONCE(jiffies);
	cputime_t delta, other;

	delta = jiffies_to_cputime(now - tsk->vtime_snap);
	other = account_other_time(delta);
	WARN_ON_ONCE(tsk->vtime_snap_whence == VTIME_INACTIVE);
	tsk->vtime_snap = now;

	return delta - other;
}

static void __vtime_account_system(struct task_struct *tsk)
{
	cputime_t delta_cpu = get_vtime_delta(tsk);

	account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
}

void vtime_account_system(struct task_struct *tsk)
{
	if (!vtime_delta(tsk))
		return;

	write_seqcount_begin(&tsk->vtime_seqcount);
	__vtime_account_system(tsk);
	write_seqcount_end(&tsk->vtime_seqcount);
}

void vtime_account_user(struct task_struct *tsk)
{
	cputime_t delta_cpu;

	write_seqcount_begin(&tsk->vtime_seqcount);
	tsk->vtime_snap_whence = VTIME_SYS;
	if (vtime_delta(tsk)) {
		delta_cpu = get_vtime_delta(tsk);
		account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
	}
	write_seqcount_end(&tsk->vtime_seqcount);
}

void vtime_user_enter(struct task_struct *tsk)
{
	write_seqcount_begin(&tsk->vtime_seqcount);
	if (vtime_delta(tsk))
		__vtime_account_system(tsk);
	tsk->vtime_snap_whence = VTIME_USER;
	write_seqcount_end(&tsk->vtime_seqcount);
}

void vtime_guest_enter(struct task_struct *tsk)
{
	/*
	 * The flags must be updated under the lock with
	 * the vtime_snap flush and update.
	 * That enforces a right ordering and update sequence
	 * synchronization against the reader (task_gtime())
	 * that can thus safely catch up with a tickless delta.
	 */
	write_seqcount_begin(&tsk->vtime_seqcount);
	if (vtime_delta(tsk))
		__vtime_account_system(tsk);
	current->flags |= PF_VCPU;
	write_seqcount_end(&tsk->vtime_seqcount);
}
EXPORT_SYMBOL_GPL(vtime_guest_enter);

void vtime_guest_exit(struct task_struct *tsk)
{
	write_seqcount_begin(&tsk->vtime_seqcount);
	__vtime_account_system(tsk);
	current->flags &= ~PF_VCPU;
	write_seqcount_end(&tsk->vtime_seqcount);
}
EXPORT_SYMBOL_GPL(vtime_guest_exit);

void vtime_account_idle(struct task_struct *tsk)
{
	cputime_t delta_cpu = get_vtime_delta(tsk);

	account_idle_time(delta_cpu);
}

void arch_vtime_task_switch(struct task_struct *prev)
{
	write_seqcount_begin(&prev->vtime_seqcount);
	prev->vtime_snap_whence = VTIME_INACTIVE;
	write_seqcount_end(&prev->vtime_seqcount);

	write_seqcount_begin(&current->vtime_seqcount);
	current->vtime_snap_whence = VTIME_SYS;
	current->vtime_snap = jiffies;
	write_seqcount_end(&current->vtime_seqcount);
}

void vtime_init_idle(struct task_struct *t, int cpu)
{
	unsigned long flags;

	local_irq_save(flags);
	write_seqcount_begin(&t->vtime_seqcount);
	t->vtime_snap_whence = VTIME_SYS;
	t->vtime_snap = jiffies;
	write_seqcount_end(&t->vtime_seqcount);
	local_irq_restore(flags);
}

cputime_t task_gtime(struct task_struct *t)
{
	unsigned int seq;
	cputime_t gtime;

	if (!vtime_accounting_enabled())
		return t->gtime;

	do {
		seq = read_seqcount_begin(&t->vtime_seqcount);

		gtime = t->gtime;
		if (t->vtime_snap_whence == VTIME_SYS && t->flags & PF_VCPU)
			gtime += vtime_delta(t);

	} while (read_seqcount_retry(&t->vtime_seqcount, seq));

	return gtime;
}

/*
 * Fetch cputime raw values from fields of task_struct and
 * add up the pending nohz execution time since the last
 * cputime snapshot.
 */
static void
fetch_task_cputime(struct task_struct *t,
		   cputime_t *u_dst, cputime_t *s_dst,
		   cputime_t *u_src, cputime_t *s_src,
		   cputime_t *udelta, cputime_t *sdelta)
{
	unsigned int seq;
	unsigned long long delta;

	do {
		*udelta = 0;
		*sdelta = 0;

		seq = read_seqcount_begin(&t->vtime_seqcount);

		if (u_dst)
			*u_dst = *u_src;
		if (s_dst)
			*s_dst = *s_src;

		/* Task is sleeping, nothing to add */
		if (t->vtime_snap_whence == VTIME_INACTIVE ||
		    is_idle_task(t))
			continue;

		delta = vtime_delta(t);

		/*
		 * Task runs either in user or kernel space, add pending nohz time to
		 * the right place.
		 */
		if (t->vtime_snap_whence == VTIME_USER || t->flags & PF_VCPU) {
			*udelta = delta;
		} else {
			if (t->vtime_snap_whence == VTIME_SYS)
				*sdelta = delta;
		}
	} while (read_seqcount_retry(&t->vtime_seqcount, seq));
}


void task_cputime(struct task_struct *t, cputime_t *utime, cputime_t *stime)
{
	cputime_t udelta, sdelta;

	if (!vtime_accounting_enabled()) {
		if (utime)
			*utime = t->utime;
		if (stime)
			*stime = t->stime;
		return;
	}

	fetch_task_cputime(t, utime, stime, &t->utime,
			   &t->stime, &udelta, &sdelta);
	if (utime)
		*utime += udelta;
	if (stime)
		*stime += sdelta;
}

void task_cputime_scaled(struct task_struct *t,
			 cputime_t *utimescaled, cputime_t *stimescaled)
{
	cputime_t udelta, sdelta;

	if (!vtime_accounting_enabled()) {
		if (utimescaled)
			*utimescaled = t->utimescaled;
		if (stimescaled)
			*stimescaled = t->stimescaled;
		return;
	}

	fetch_task_cputime(t, utimescaled, stimescaled,
			   &t->utimescaled, &t->stimescaled, &udelta, &sdelta);
	if (utimescaled)
		*utimescaled += cputime_to_scaled(udelta);
	if (stimescaled)
		*stimescaled += cputime_to_scaled(sdelta);
}
#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */