#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 <linux/sched/cputime.h>

  #include "sched.h"

  
  #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(struct irqtime, cpu_irqtime);

  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;
  }

  static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
  				  enum cpu_usage_stat idx)
  {
  	u64 *cpustat = kcpustat_this_cpu->cpustat;
  
  	u64_stats_update_begin(&irqtime->sync);
  	cpustat[idx] += delta;
  	irqtime->total += delta;
  	irqtime->tick_delta += delta;
  	u64_stats_update_end(&irqtime->sync);
  }

  /*
   * 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)

  {

  	struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);

  	s64 delta;
  	int cpu;
  
  	if (!sched_clock_irqtime)
  		return;

  	cpu = smp_processor_id();

  	delta = sched_clock_cpu(cpu) - irqtime->irq_start_time;
  	irqtime->irq_start_time += delta;

  	/*
  	 * 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())
  		irqtime_account_delta(irqtime, delta, CPUTIME_IRQ);
  	else if (in_serving_softirq() && curr != this_cpu_ksoftirqd())
  		irqtime_account_delta(irqtime, delta, CPUTIME_SOFTIRQ);

  }

  EXPORT_SYMBOL_GPL(irqtime_account_irq);

  static u64 irqtime_tick_accounted(u64 maxtime)

  {

  	struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);

  	u64 delta;

  	delta = min(irqtime->tick_delta, maxtime);
  	irqtime->tick_delta -= delta;

  	return delta;

  }
  
  #else /* CONFIG_IRQ_TIME_ACCOUNTING */
  
  #define sched_clock_irqtime	(0)

  static u64 irqtime_tick_accounted(u64 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

   */

  void account_user_time(struct task_struct *p, u64 cputime)

  {
  	int index;
  
  	/* Add user time to process. */

  	p->utime += cputime;
  	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, 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

   */

  void account_guest_time(struct task_struct *p, u64 cputime)

  {
  	u64 *cpustat = kcpustat_this_cpu->cpustat;
  
  	/* Add guest time to process. */

  	p->utime += cputime;
  	account_group_user_time(p, cputime);
  	p->gtime += cputime;

  
  	/* Add guest time to cpustat. */

  	if (task_nice(p) > 0) {

  		cpustat[CPUTIME_NICE] += cputime;
  		cpustat[CPUTIME_GUEST_NICE] += cputime;

  	} else {

  		cpustat[CPUTIME_USER] += cputime;
  		cpustat[CPUTIME_GUEST] += 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

   * @index: pointer to cpustat field that has to be updated

   */

  void account_system_index_time(struct task_struct *p,

  			       u64 cputime, enum cpu_usage_stat index)

  {
  	/* Add system time to process. */

  	p->stime += cputime;
  	account_group_system_time(p, cputime);

  
  	/* Add system time to cpustat. */

  	task_group_account_field(p, index, 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

   */

  void account_system_time(struct task_struct *p, int hardirq_offset, u64 cputime)

  {
  	int index;
  
  	if ((p->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) {

  		account_guest_time(p, cputime);

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

  	account_system_index_time(p, cputime, index);

  }
  
  /*
   * Account for involuntary wait time.
   * @cputime: the cpu time spent in involuntary wait
   */

  void account_steal_time(u64 cputime)

  {
  	u64 *cpustat = kcpustat_this_cpu->cpustat;

  	cpustat[CPUTIME_STEAL] += cputime;

  }
  
  /*
   * Account for idle time.
   * @cputime: the cpu time spent in idle wait
   */

  void account_idle_time(u64 cputime)

  {
  	u64 *cpustat = kcpustat_this_cpu->cpustat;
  	struct rq *rq = this_rq();
  
  	if (atomic_read(&rq->nr_iowait) > 0)

  		cpustat[CPUTIME_IOWAIT] += cputime;

  	else

  		cpustat[CPUTIME_IDLE] += cputime;

  }

  /*
   * When a guest is interrupted for a longer amount of time, missed clock
   * ticks are not redelivered later. Due to that, this function may on
   * occasion account more time than the calling functions think elapsed.
   */

  static __always_inline u64 steal_account_process_time(u64 maxtime)

  {
  #ifdef CONFIG_PARAVIRT
  	if (static_key_false(&paravirt_steal_enabled)) {

  		u64 steal;

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

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

  		return steal;

  	}
  #endif

  	return 0;

  }

  /*

   * Account how much elapsed time was spent in steal, irq, or softirq time.
   */

  static inline u64 account_other_time(u64 max)

  {

  	u64 accounted;

  	/* Shall be converted to a lockdep-enabled lightweight check */
  	WARN_ON_ONCE(!irqs_disabled());

  	accounted = steal_account_process_time(max);
  
  	if (accounted < max)

  		accounted += irqtime_tick_accounted(max - accounted);

  
  	return accounted;
  }

  #ifdef CONFIG_64BIT
  static inline u64 read_sum_exec_runtime(struct task_struct *t)
  {
  	return t->se.sum_exec_runtime;
  }
  #else
  static u64 read_sum_exec_runtime(struct task_struct *t)
  {
  	u64 ns;
  	struct rq_flags rf;
  	struct rq *rq;
  
  	rq = task_rq_lock(t, &rf);
  	ns = t->se.sum_exec_runtime;
  	task_rq_unlock(rq, t, &rf);
  
  	return ns;
  }
  #endif

  /*

   * 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;

  	u64 utime, stime;

  	struct task_struct *t;

  	unsigned int seq, nextseq;

  	unsigned long flags;

  	/*
  	 * Update current task runtime to account pending time since last
  	 * scheduler action or thread_group_cputime() call. This thread group
  	 * might have other running tasks on different CPUs, but updating
  	 * their runtime can affect syscall performance, so we skip account
  	 * those pending times and rely only on values updated on tick or
  	 * other scheduler action.
  	 */
  	if (same_thread_group(current, tsk))
  		(void) task_sched_runtime(current);

  	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 += read_sum_exec_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 other, cputime = TICK_NSEC * ticks;

  	/*
  	 * 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(ULONG_MAX);

  	if (other >= cputime)

  		return;

  	cputime -= other;

  	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_index_time(p, cputime, CPUTIME_SOFTIRQ);

  	} else if (user_tick) {

  		account_user_time(p, cputime);

  	} 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);

  	} else {

  		account_system_index_time(p, cputime, 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);

  	vtime_flush(prev);

  	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, u64 *ut, u64 *st)

  {
  	*ut = p->utime;
  	*st = p->stime;
  }

  EXPORT_SYMBOL_GPL(task_cputime_adjusted);

  void thread_group_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *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)

  {

  	u64 cputime, 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 = TICK_NSEC;

  	steal = steal_account_process_time(ULONG_MAX);

  	if (steal >= cputime)

  		return;

  	cputime -= steal;

  	if (user_tick)

  		account_user_time(p, cputime);

  	else if ((p != rq->idle) || (irq_count() != HARDIRQ_OFFSET))

  		account_system_time(p, HARDIRQ_OFFSET, cputime);

  	else

  		account_idle_time(cputime);

  }

  /*

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

  	u64 cputime, steal;

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

  	cputime = ticks * TICK_NSEC;

  	steal = steal_account_process_time(ULONG_MAX);

  
  	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 u64 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 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,

  			   u64 *ut, u64 *st)

  {

  	u64 rtime, stime, utime;

  	unsigned long flags;

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

  	rtime = 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 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(stime, rtime, 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, u64 *ut, u64 *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, u64 *ut, u64 *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 u64 vtime_delta(struct vtime *vtime)

  {

  	unsigned long long clock;

  	clock = sched_clock();

  	if (clock < vtime->starttime)

  		return 0;

  	return clock - vtime->starttime;

  }

  static u64 get_vtime_delta(struct vtime *vtime)

  {

  	u64 delta = vtime_delta(vtime);
  	u64 other;

  	/*
  	 * Unlike tick based timing, vtime based timing never has lost
  	 * ticks, and no need for steal time accounting to make up for
  	 * lost ticks. Vtime accounts a rounded version of actual
  	 * elapsed time. Limit account_other_time to prevent rounding
  	 * errors from causing elapsed vtime to go negative.
  	 */

  	other = account_other_time(delta);

  	WARN_ON_ONCE(vtime->state == VTIME_INACTIVE);

  	vtime->starttime += delta;

  	return delta - other;

  }

  static void __vtime_account_system(struct task_struct *tsk,
  				   struct vtime *vtime)

  {

  	vtime->stime += get_vtime_delta(vtime);
  	if (vtime->stime >= TICK_NSEC) {
  		account_system_time(tsk, irq_count(), vtime->stime);
  		vtime->stime = 0;
  	}
  }
  
  static void vtime_account_guest(struct task_struct *tsk,
  				struct vtime *vtime)
  {
  	vtime->gtime += get_vtime_delta(vtime);
  	if (vtime->gtime >= TICK_NSEC) {
  		account_guest_time(tsk, vtime->gtime);
  		vtime->gtime = 0;
  	}

  }

  void vtime_account_system(struct task_struct *tsk)
  {

  	struct vtime *vtime = &tsk->vtime;
  
  	if (!vtime_delta(vtime))

  		return;

  	write_seqcount_begin(&vtime->seqcount);

  	/* We might have scheduled out from guest path */
  	if (current->flags & PF_VCPU)
  		vtime_account_guest(tsk, vtime);
  	else
  		__vtime_account_system(tsk, vtime);

  	write_seqcount_end(&vtime->seqcount);

  }

  void vtime_user_enter(struct task_struct *tsk)

  {

  	struct vtime *vtime = &tsk->vtime;
  
  	write_seqcount_begin(&vtime->seqcount);

  	__vtime_account_system(tsk, vtime);

  	vtime->state = VTIME_USER;
  	write_seqcount_end(&vtime->seqcount);

  }

  void vtime_user_exit(struct task_struct *tsk)

  {

  	struct vtime *vtime = &tsk->vtime;
  
  	write_seqcount_begin(&vtime->seqcount);

  	vtime->utime += get_vtime_delta(vtime);
  	if (vtime->utime >= TICK_NSEC) {
  		account_user_time(tsk, vtime->utime);
  		vtime->utime = 0;
  	}

  	vtime->state = VTIME_SYS;
  	write_seqcount_end(&vtime->seqcount);

  }
  
  void vtime_guest_enter(struct task_struct *tsk)
  {

  	struct vtime *vtime = &tsk->vtime;

  	/*
  	 * The flags must be updated under the lock with

  	 * the vtime_starttime 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(&vtime->seqcount);

  	__vtime_account_system(tsk, vtime);

  	current->flags |= PF_VCPU;

  	write_seqcount_end(&vtime->seqcount);

  }

  EXPORT_SYMBOL_GPL(vtime_guest_enter);

  
  void vtime_guest_exit(struct task_struct *tsk)
  {

  	struct vtime *vtime = &tsk->vtime;
  
  	write_seqcount_begin(&vtime->seqcount);

  	vtime_account_guest(tsk, vtime);

  	current->flags &= ~PF_VCPU;

  	write_seqcount_end(&vtime->seqcount);

  }

  EXPORT_SYMBOL_GPL(vtime_guest_exit);

  
  void vtime_account_idle(struct task_struct *tsk)
  {

  	account_idle_time(get_vtime_delta(&tsk->vtime));

  }

  void arch_vtime_task_switch(struct task_struct *prev)
  {

  	struct vtime *vtime = &prev->vtime;

  	write_seqcount_begin(&vtime->seqcount);
  	vtime->state = VTIME_INACTIVE;
  	write_seqcount_end(&vtime->seqcount);
  
  	vtime = &current->vtime;
  
  	write_seqcount_begin(&vtime->seqcount);
  	vtime->state = VTIME_SYS;

  	vtime->starttime = sched_clock();

  	write_seqcount_end(&vtime->seqcount);

  }

  void vtime_init_idle(struct task_struct *t, int cpu)

  {

  	struct vtime *vtime = &t->vtime;

  	unsigned long flags;

  	local_irq_save(flags);

  	write_seqcount_begin(&vtime->seqcount);
  	vtime->state = VTIME_SYS;

  	vtime->starttime = sched_clock();

  	write_seqcount_end(&vtime->seqcount);

  	local_irq_restore(flags);

  }

  u64 task_gtime(struct task_struct *t)

  {

  	struct vtime *vtime = &t->vtime;

  	unsigned int seq;

  	u64 gtime;

  	if (!vtime_accounting_enabled())

  		return t->gtime;

  	do {

  		seq = read_seqcount_begin(&vtime->seqcount);

  
  		gtime = t->gtime;

  		if (vtime->state == VTIME_SYS && t->flags & PF_VCPU)

  			gtime += vtime->gtime + vtime_delta(vtime);

  	} while (read_seqcount_retry(&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.
   */

  void task_cputime(struct task_struct *t, u64 *utime, u64 *stime)

  {

  	struct vtime *vtime = &t->vtime;

  	unsigned int seq;

  	u64 delta;

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

  	do {

  		seq = read_seqcount_begin(&vtime->seqcount);

  		*utime = t->utime;
  		*stime = t->stime;

  
  		/* Task is sleeping, nothing to add */

  		if (vtime->state == VTIME_INACTIVE || is_idle_task(t))

  			continue;

  		delta = vtime_delta(vtime);

  
  		/*
  		 * Task runs either in user or kernel space, add pending nohz time to
  		 * the right place.
  		 */

  		if (vtime->state == VTIME_USER || t->flags & PF_VCPU)

  			*utime += vtime->utime + delta;

  		else if (vtime->state == VTIME_SYS)

  			*stime += vtime->stime + delta;

  	} while (read_seqcount_retry(&vtime->seqcount, seq));

  }

  #endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */