cputime.c

Go to the documentation of this file.

#include <linux/export.h>
#include <linux/sched.h>
#include <linux/tsacct_kern.h>
#include <linux/kernel_stat.h>
#include <linux/static_key.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(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 vtime_account(struct task_struct *curr)
{
    unsigned long flags;
    s64 delta;
    int cpu;

    if (!sched_clock_irqtime)
        return;

    local_irq_save(flags);

    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();
    local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(vtime_account);

static int irqtime_account_hi_update(void)
{
    u64 *cpustat = kcpustat_this_cpu->cpustat;
    unsigned long flags;
    u64 latest_ns;
    int ret = 0;

    local_irq_save(flags);
    latest_ns = this_cpu_read(cpu_hardirq_time);
    if (nsecs_to_cputime64(latest_ns) > cpustat[CPUTIME_IRQ])
        ret = 1;
    local_irq_restore(flags);
    return ret;
}

static int irqtime_account_si_update(void)
{
    u64 *cpustat = kcpustat_this_cpu->cpustat;
    unsigned long flags;
    u64 latest_ns;
    int ret = 0;

    local_irq_save(flags);
    latest_ns = this_cpu_read(cpu_softirq_time);
    if (nsecs_to_cputime64(latest_ns) > cpustat[CPUTIME_SOFTIRQ])
        ret = 1;
    local_irq_restore(flags);
    return ret;
}

#else /* CONFIG_IRQ_TIME_ACCOUNTING */

#define sched_clock_irqtime (0)

#endif /* !CONFIG_IRQ_TIME_ACCOUNTING */

static inline void task_group_account_field(struct task_struct *p, int index,
                        u64 tmp)
{
#ifdef CONFIG_CGROUP_CPUACCT
    struct kernel_cpustat *kcpustat;
    struct cpuacct *ca;
#endif
    /*
     * 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.
     *
     */
    __get_cpu_var(kernel_cpustat).cpustat[index] += tmp;

#ifdef CONFIG_CGROUP_CPUACCT
    if (unlikely(!cpuacct_subsys.active))
        return;

    rcu_read_lock();
    ca = task_ca(p);
    while (ca && (ca != &root_cpuacct)) {
        kcpustat = this_cpu_ptr(ca->cpustat);
        kcpustat->cpustat[index] += tmp;
        ca = parent_ca(ca);
    }
    rcu_read_unlock();
#endif
}

/*
 * 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_update_integrals(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_update_integrals(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 bool steal_account_process_tick(void)
{
#ifdef CONFIG_PARAVIRT
    if (static_key_false(&paravirt_steal_enabled)) {
        u64 steal, st = 0;

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

        st = steal_ticks(steal);
        this_rq()->prev_steal_time += st * TICK_NSEC;

        account_steal_time(st);
        return st;
    }
#endif
    return false;
}

#ifndef CONFIG_VIRT_CPU_ACCOUNTING

#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)
{
    cputime_t one_jiffy_scaled = cputime_to_scaled(cputime_one_jiffy);
    u64 *cpustat = kcpustat_this_cpu->cpustat;

    if (steal_account_process_tick())
        return;

    if (irqtime_account_hi_update()) {
        cpustat[CPUTIME_IRQ] += (__force u64) cputime_one_jiffy;
    } else if (irqtime_account_si_update()) {
        cpustat[CPUTIME_SOFTIRQ] += (__force u64) cputime_one_jiffy;
    } else 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_one_jiffy, one_jiffy_scaled,
                    CPUTIME_SOFTIRQ);
    } else if (user_tick) {
        account_user_time(p, cputime_one_jiffy, one_jiffy_scaled);
    } else if (p == rq->idle) {
        account_idle_time(cputime_one_jiffy);
    } else if (p->flags & PF_VCPU) { /* System time or guest time */
        account_guest_time(p, cputime_one_jiffy, one_jiffy_scaled);
    } else {
        __account_system_time(p, cputime_one_jiffy, one_jiffy_scaled,
                    CPUTIME_SYSTEM);
    }
}

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

    for (i = 0; i < ticks; i++)
        irqtime_account_process_tick(current, 0, rq);
}
#else /* CONFIG_IRQ_TIME_ACCOUNTING */
static void irqtime_account_idle_ticks(int ticks) {}
static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
                        struct rq *rq) {}
#endif /* CONFIG_IRQ_TIME_ACCOUNTING */

/*
 * 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 one_jiffy_scaled = cputime_to_scaled(cputime_one_jiffy);
    struct rq *rq = this_rq();

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

    if (steal_account_process_tick())
        return;

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

/*
 * Account multiple ticks of steal time.
 * @p: the process from which the cpu time has been stolen
 * @ticks: number of stolen ticks
 */
void account_steal_ticks(unsigned long ticks)
{
    account_steal_time(jiffies_to_cputime(ticks));
}

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

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

    account_idle_time(jiffies_to_cputime(ticks));
}

#endif

/*
 * Use precise platform statistics if available:
 */
#ifdef CONFIG_VIRT_CPU_ACCOUNTING
void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
    *ut = p->utime;
    *st = p->stime;
}

void thread_group_times(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;
}

/*
 * 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(struct task_struct *tsk)
{
    unsigned long flags;

    local_irq_save(flags);

    if (in_interrupt() || !is_idle_task(tsk))
        vtime_account_system(tsk);
    else
        vtime_account_idle(tsk);

    local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(vtime_account);
#endif /* __ARCH_HAS_VTIME_ACCOUNT */

#else

#ifndef nsecs_to_cputime
# define nsecs_to_cputime(__nsecs)  nsecs_to_jiffies(__nsecs)
#endif

static cputime_t scale_utime(cputime_t utime, cputime_t rtime, cputime_t total)
{
    u64 temp = (__force u64) rtime;

    temp *= (__force u64) utime;

    if (sizeof(cputime_t) == 4)
        temp = div_u64(temp, (__force u32) total);
    else
        temp = div64_u64(temp, (__force u64) total);

    return (__force cputime_t) temp;
}

void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
    cputime_t rtime, utime = p->utime, total = utime + p->stime;

    /*
     * Use CFS's precise accounting:
     */
    rtime = nsecs_to_cputime(p->se.sum_exec_runtime);

    if (total)
        utime = scale_utime(utime, rtime, total);
    else
        utime = rtime;

    /*
     * Compare with previous values, to keep monotonicity:
     */
    p->prev_utime = max(p->prev_utime, utime);
    p->prev_stime = max(p->prev_stime, rtime - p->prev_utime);

    *ut = p->prev_utime;
    *st = p->prev_stime;
}

/*
 * Must be called with siglock held.
 */
void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
    struct signal_struct *sig = p->signal;
    struct task_cputime cputime;
    cputime_t rtime, utime, total;

    thread_group_cputime(p, &cputime);

    total = cputime.utime + cputime.stime;
    rtime = nsecs_to_cputime(cputime.sum_exec_runtime);

    if (total)
        utime = scale_utime(cputime.utime, rtime, total);
    else
        utime = rtime;

    sig->prev_utime = max(sig->prev_utime, utime);
    sig->prev_stime = max(sig->prev_stime, rtime - sig->prev_utime);

    *ut = sig->prev_utime;
    *st = sig->prev_stime;
}
#endif