diff options
Diffstat (limited to 'kernel/time/tick-sched.c')
| -rw-r--r-- | kernel/time/tick-sched.c | 563 |
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; +} |