path: root/kernel/time/tick-sched.c

/*
 *  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 <asm/irq_regs.h>

#include "tick-internal.h"

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

/*
 * The time, when the last jiffy update happened. Protected by xtime_lock.
 */
static ktime_t last_jiffies_update;

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

/*
 * 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 xtime_lock:
	 */
	delta = ktime_sub(now, last_jiffies_update);
	if (delta.tv64 < tick_period.tv64)
		return;

	/* Reevalute with xtime_lock held */
	write_seqlock(&xtime_lock);

	delta = ktime_sub(now, last_jiffies_update);
	if (delta.tv64 >= tick_period.tv64) {

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

		/* Slow path for long timeouts */
		if (unlikely(delta.tv64 >= tick_period.tv64)) {
			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);
	}
	write_sequnlock(&xtime_lock);
}

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

	write_seqlock(&xtime_lock);
	/* Did we start the jiffies update yet ? */
	if (last_jiffies_update.tv64 == 0)
		last_jiffies_update = tick_next_period;
	period = last_jiffies_update;
	write_sequnlock(&xtime_lock);
	return period;
}

/*
 * NOHZ - aka dynamic tick functionality
 */
#ifdef CONFIG_NO_HZ
/*
 * NO HZ enabled ?
 */
int tick_nohz_enabled __read_mostly  = 1;

/*
 * Enable / Disable tickless mode
 */
static int __init setup_tick_nohz(char *str)
{
	if (!strcmp(str, "off"))
		tick_nohz_enabled = 0;
	else if (!strcmp(str, "on"))
		tick_nohz_enabled = 1;
	else
		return 0;
	return 1;
}

__setup("nohz=", setup_tick_nohz);

/**
 * 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)
{
	int cpu = smp_processor_id();
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
	unsigned long flags;

	ts->idle_waketime = now;

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

	touch_softlockup_watchdog();
}

/*
 * 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(int cpu, ktime_t now)
{
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

	update_ts_time_stats(cpu, ts, now, NULL);
	ts->idle_active = 0;

	sched_clock_idle_wakeup_event(0);
}

static ktime_t tick_nohz_start_idle(int cpu, 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 cummulative idle time (since boot) for a given