cputime: Comment cputime's adjusting code

[deliverable/linux.git] / kernel / sched / cputime.c

#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 irqtime_account_irq(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(irqtime_account_irq);

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;
}

/*
 * 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;
        struct task_struct *t;

        times->utime = sig->utime;
        times->stime = sig->stime;
        times->sum_exec_runtime = sig->sum_sched_runtime;

        rcu_read_lock();
        /* make sure we can trust tsk->thread_group list */
        if (!likely(pid_alive(tsk)))
                goto out;

        t = tsk;
        do {
                times->utime += t->utime;
                times->stime += t->stime;
                times->sum_exec_runtime += task_sched_runtime(t);
        } while_each_thread(tsk, t);
out:
        rcu_read_unlock();
}

#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_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
        *ut = p->utime;
        *st = p->stime;
}

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;
}

void vtime_account_system(struct task_struct *tsk)
{
        unsigned long flags;

        local_irq_save(flags);
        __vtime_account_system(tsk);
        local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(vtime_account_system);

/*
 * 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;
}

/*
 * Adjust tick based cputime random precision against scheduler
 * runtime accounting.
 */
static void cputime_adjust(struct task_cputime *curr,
                           struct cputime *prev,
                           cputime_t *ut, cputime_t *st)
{
        cputime_t rtime, utime, total;

        utime = curr->utime;
        total = utime + curr->stime;

        /*
         * 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.
         */
        rtime = nsecs_to_cputime(curr->sum_exec_runtime);

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

        /*
         * If the tick based count grows faster than the scheduler one,
         * the result of the scaling may go backward.
         * Let's enforce monotonicity.
         */
        prev->utime = max(prev->utime, utime);
        prev->stime = max(prev->stime, rtime - prev->utime);

        *ut = prev->utime;
        *st = prev->stime;
}

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

        cputime_adjust(&cputime, &p->prev_cputime, ut, st);
}

/*
 * Must be called with siglock held.
 */
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