1 files changed, 563 insertions, 0 deletions

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
new file mode 100644
index 000000000000..95e41f7f850b
--- /dev/null
+++ b/kernel/time/tick-sched.c
@@ -0,0 +1,563 @@
+/*
+ *  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
+ *
+ *  For licencing details see kernel-base/COPYING
+ */
+#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/tick.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;
+
+        /* 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);
+        }
+        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 ?
+ */
+static 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.
+ */
+void tick_nohz_update_jiffies(void)
+{
+        int cpu = smp_processor_id();
+        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+        unsigned long flags;
+        ktime_t now;
+
+        if (!ts->tick_stopped)
+                return;
+
+        cpu_clear(cpu, nohz_cpu_mask);
+        now = ktime_get();
+
+        local_irq_save(flags);
+        tick_do_update_jiffies64(now);
+        local_irq_restore(flags);
+}
+
+/**
+ * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
+ *
+ * When the next event is more than a tick into the future, stop the idle tick
+ * Called either from the idle loop or from irq_exit() when an idle period was
+ * just interrupted by an interrupt which did not cause a reschedule.
+ */
+void tick_nohz_stop_sched_tick(void)
+{
+        unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
+        struct tick_sched *ts;
+        ktime_t last_update, expires, now, delta;
+        int cpu;
+
+        local_irq_save(flags);
+
+        cpu = smp_processor_id();
+        ts = &per_cpu(tick_cpu_sched, cpu);
+
+        if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
+                goto end;
+
+        if (need_resched())
+                goto end;
+
+        cpu = smp_processor_id();
+        BUG_ON(local_softirq_pending());
+
+        now = ktime_get();
+        /*
+         * When called from irq_exit we need to account the idle sleep time
+         * correctly.
+         */
+        if (ts->tick_stopped) {
+                delta = ktime_sub(now, ts->idle_entrytime);
+                ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
+        }
+
+        ts->idle_entrytime = now;
+        ts->idle_calls++;
+
+        /* Read jiffies and the time when jiffies were updated last */
+        do {
+                seq = read_seqbegin(&xtime_lock);
+                last_update = last_jiffies_update;
+                last_jiffies = jiffies;
+        } while (read_seqretry(&xtime_lock, seq));
+
+        /* Get the next timer wheel timer */
+        next_jiffies = get_next_timer_interrupt(last_jiffies);
+        delta_jiffies = next_jiffies - last_jiffies;
+
+        /*
+         * Do not stop the tick, if we are only one off
+         * or if the cpu is required for rcu
+         */
+        if (!ts->tick_stopped && (delta_jiffies == 1 || rcu_needs_cpu(cpu)))
+                goto out;
+
+        /* Schedule the tick, if we are at least one jiffie off */
+        if ((long)delta_jiffies >= 1) {
+
+                if (rcu_needs_cpu(cpu))
+                        delta_jiffies = 1;
+                else
+                        cpu_set(cpu, nohz_cpu_mask);
+                /*
+                 * nohz_stop_sched_tick can be called several times before
+                 * the nohz_restart_sched_tick is called. This happens when
+                 * interrupts arrive which do not cause a reschedule. In the
+                 * first call we save the current tick time, so we can restart
+                 * the scheduler tick in nohz_restart_sched_tick.
+                 */
+                if (!ts->tick_stopped) {
+                        ts->idle_tick = ts->sched_timer.expires;
+                        ts->tick_stopped = 1;
+                        ts->idle_jiffies = last_jiffies;
+                }
+                /*
+                 * calculate the expiry time for the next timer wheel
+                 * timer
+                 */
+                expires = ktime_add_ns(last_update, tick_period.tv64 *
+                                       delta_jiffies);
+                ts->idle_expires = expires;
+                ts->idle_sleeps++;
+
+                if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
+                        hrtimer_start(&ts->sched_timer, expires,
+                                      HRTIMER_MODE_ABS);
+                        /* Check, if the timer was already in the past */
+                        if (hrtimer_active(&ts->sched_timer))
+                                goto out;
+                } else if(!tick_program_event(expires, 0))
+                                goto out;
+                /*
+                 * We are past the event already. So we crossed a
+                 * jiffie boundary. Update jiffies and raise the
+                 * softirq.
+                 */
+                tick_do_update_jiffies64(ktime_get());
+                cpu_clear(cpu, nohz_cpu_mask);
+        }
+        raise_softirq_irqoff(TIMER_SOFTIRQ);
+out:
+        ts->next_jiffies = next_jiffies;
+        ts->last_jiffies = last_jiffies;
+end:
+        local_irq_restore(flags);
+}
+
+/**
+ * nohz_restart_sched_tick - restart the idle tick from the idle task
+ *
+ * Restart the idle tick when the CPU is woken up from idle
+ */
+void tick_nohz_restart_sched_tick(void)
+{
+        int cpu = smp_processor_id();
+        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+        unsigned long ticks;
+        ktime_t now, delta;
+
+        if (!ts->tick_stopped)
+                return;
+
+        /* Update jiffies first */
+        now = ktime_get();
+
+        local_irq_disable();
+        tick_do_update_jiffies64(now);
+        cpu_clear(cpu, nohz_cpu_mask);
+
+        /* Account the idle time */
+        delta = ktime_sub(now, ts->idle_entrytime);
+        ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
+
+        /*
+         * We stopped the tick in idle. Update process times would miss the
+         * time we slept as update_process_times does only a 1 tick
+         * accounting. Enforce that this is accounted to idle !
+         */
+        ticks = jiffies - ts->idle_jiffies;
+        /*
+         * We might be one off. Do not randomly account a huge number of ticks!
+         */
+        if (ticks && ticks < LONG_MAX) {
+                add_preempt_count(HARDIRQ_OFFSET);
+                account_system_time(current, HARDIRQ_OFFSET,
+                                    jiffies_to_cputime(ticks));
+                sub_preempt_count(HARDIRQ_OFFSET);
+        }
+
+        /*
+         * Cancel the scheduled timer and restore the tick
+         */
+        ts->tick_stopped  = 0;
+        hrtimer_cancel(&ts->sched_timer);
+        ts->sched_timer.expires = ts->idle_tick;
+
+        while (1) {
+                /* Forward the time to expire in the future */
+                hrtimer_forward(&ts->sched_timer, now, tick_period);
+
+                if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
+                        hrtimer_start(&ts->sched_timer,
+                                      ts->sched_timer.expires,
+                                      HRTIMER_MODE_ABS);
+                        /* Check, if the timer was already in the past */
+                        if (hrtimer_active(&ts->sched_timer))
+                                break;
+                } else {
+                        if (!tick_program_event(ts->sched_timer.expires, 0))
+                                break;
+                }
+                /* Update jiffies and reread time */
+                tick_do_update_jiffies64(now);
+                now = ktime_get();
+        }
+        local_irq_enable();
+}
+
+static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
+{
+        hrtimer_forward(&ts->sched_timer, now, tick_period);
+        return tick_program_event(ts->sched_timer.expires, 0);
+}
+
+/*
+ * The nohz low res interrupt handler
+ */
+static void tick_nohz_handler(struct clock_event_device *dev)
+{
+        struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+        struct pt_regs *regs = get_irq_regs();
+        ktime_t now = ktime_get();
+
+        dev->next_event.tv64 = KTIME_MAX;
+
+        /* Check, if the jiffies need an update */
+        tick_do_update_jiffies64(now);
+
+        /*
+         * When we are idle and the tick is stopped, we have to touch
+         * the watchdog as we might not schedule for a really long
+         * time. This happens on complete idle SMP systems while
+         * waiting on the login prompt. We also increment the "start
+         * of idle" jiffy stamp so the idle accounting adjustment we
+         * do when we go busy again does not account too much ticks.
+         */
+        if (ts->tick_stopped) {
+                touch_softlockup_watchdog();
+                ts->idle_jiffies++;
+        }
+
+        update_process_times(user_mode(regs));
+        profile_tick(CPU_PROFILING);
+
+        /* Do not restart, when we are in the idle loop */
+        if (ts->tick_stopped)
+                return;
+
+        while (tick_nohz_reprogram(ts, now)) {
+                now = ktime_get();
+                tick_do_update_jiffies64(now);
+        }
+}
+
+/**
+ * tick_nohz_switch_to_nohz - switch to nohz mode
+ */
+static void tick_nohz_switch_to_nohz(void)
+{
+        struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+        ktime_t next;
+
+        if (!tick_nohz_enabled)
+                return;
+
+        local_irq_disable();
+        if (tick_switch_to_oneshot(tick_nohz_handler)) {
+                local_irq_enable();
+                return;
+        }
+
+        ts->nohz_mode = NOHZ_MODE_LOWRES;
+
+        /*
+         * Recycle the hrtimer in ts, so we can share the
+         * hrtimer_forward with the highres code.
+         */
+        hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+        /* Get the next period */
+        next = tick_init_jiffy_update();
+
+        for (;;) {
+                ts->sched_timer.expires = next;
+                if (!tick_program_event(next, 0))
+                        break;
+                next = ktime_add(next, tick_period);
+        }
+        local_irq_enable();
+
+        printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
+               smp_processor_id());
+}
+
+#else
+
+static inline void tick_nohz_switch_to_nohz(void) { }
+
+#endif /* NO_HZ */
+
+/*
+ * High resolution timer specific code
+ */
+#ifdef CONFIG_HIGH_RES_TIMERS
+/*
+ * We rearm the timer until we get disabled by the idle code
+ * Called with interrupts disabled and timer->base->cpu_base->lock held.
+ */
+static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
+{
+        struct tick_sched *ts =
+                container_of(timer, struct tick_sched, sched_timer);
+        struct hrtimer_cpu_base *base = timer->base->cpu_base;
+        struct pt_regs *regs = get_irq_regs();
+        ktime_t now = ktime_get();
+
+        /* Check, if the jiffies need an update */
+        tick_do_update_jiffies64(now);
+
+        /*
+         * Do not call, when we are not in irq context and have
+         * no valid regs pointer
+         */
+        if (regs) {
+                /*
+                 * When we are idle and the tick is stopped, we have to touch
+                 * the watchdog as we might not schedule for a really long
+                 * time. This happens on complete idle SMP systems while
+                 * waiting on the login prompt. We also increment the "start of
+                 * idle" jiffy stamp so the idle accounting adjustment we do
+                 * when we go busy again does not account too much ticks.
+                 */
+                if (ts->tick_stopped) {
+                        touch_softlockup_watchdog();
+                        ts->idle_jiffies++;
+                }
+                /*
+                 * update_process_times() might take tasklist_lock, hence
+                 * drop the base lock. sched-tick hrtimers are per-CPU and
+                 * never accessible by userspace APIs, so this is safe to do.
+                 */
+                spin_unlock(&base->lock);
+                update_process_times(user_mode(regs));
+                profile_tick(CPU_PROFILING);
+                spin_lock(&base->lock);
+        }
+
+        /* Do not restart, when we are in the idle loop */
+        if (ts->tick_stopped)
+                return HRTIMER_NORESTART;
+
+        hrtimer_forward(timer, now, tick_period);
+
+        return HRTIMER_RESTART;
+}
+
+/**
+ * tick_setup_sched_timer - setup the tick emulation timer
+ */
+void tick_setup_sched_timer(void)
+{
+        struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+        ktime_t now = ktime_get();
+
+        /*
+         * Emulate tick processing via per-CPU hrtimers:
+         */
+        hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+        ts->sched_timer.function = tick_sched_timer;
+        ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+
+        /* Get the next period */
+        ts->sched_timer.expires = tick_init_jiffy_update();
+
+        for (;;) {
+                hrtimer_forward(&ts->sched_timer, now, tick_period);
+                hrtimer_start(&ts->sched_timer, ts->sched_timer.expires,
+                              HRTIMER_MODE_ABS);
+                /* Check, if the timer was already in the past */
+                if (hrtimer_active(&ts->sched_timer))
+                        break;
+                now = ktime_get();
+        }
+
+#ifdef CONFIG_NO_HZ
+        if (tick_nohz_enabled)
+                ts->nohz_mode = NOHZ_MODE_HIGHRES;
+#endif
+}
+
+void tick_cancel_sched_timer(int cpu)
+{
+        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+
+        if (ts->sched_timer.base)
+                hrtimer_cancel(&ts->sched_timer);
+        ts->tick_stopped = 0;
+        ts->nohz_mode = NOHZ_MODE_INACTIVE;
+}
+#endif /* HIGH_RES_TIMERS */
+
+/**
+ * Async notification about clocksource changes
+ */
+void tick_clock_notify(void)
+{
+        int cpu;
+
+        for_each_possible_cpu(cpu)
+                set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
+}
+
+/*
+ * Async notification about clock event changes
+ */
+void tick_oneshot_notify(void)
+{
+        struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+
+        set_bit(0, &ts->check_clocks);
+}
+
+/**
+ * Check, if a change happened, which makes oneshot possible.
+ *
+ * Called cyclic from the hrtimer softirq (driven by the timer
+ * softirq) allow_nohz signals, that we can switch into low-res nohz
+ * mode, because high resolution timers are disabled (either compile
+ * or runtime).
+ */
+int tick_check_oneshot_change(int allow_nohz)
+{
+        struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+
+        if (!test_and_clear_bit(0, &ts->check_clocks))
+                return 0;
+
+        if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
+                return 0;
+
+        if (!timekeeping_is_continuous() || !tick_is_oneshot_available())
+                return 0;
+
+        if (!allow_nohz)
+                return 1;
+
+        tick_nohz_switch_to_nohz();
+        return 0;
+}