X-Git-Url: https://gerrit.opnfv.org/gerrit/gitweb?a=blobdiff_plain;f=kernel%2Fkernel%2Ftime%2Ftick-sched.c;fp=kernel%2Fkernel%2Ftime%2Ftick-sched.c;h=b3841ba00c69e960f41e84525a1a456ec2d7d0ac;hb=9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00;hp=0000000000000000000000000000000000000000;hpb=98260f3884f4a202f9ca5eabed40b1354c489b29;p=kvmfornfv.git diff --git a/kernel/kernel/time/tick-sched.c b/kernel/kernel/time/tick-sched.c new file mode 100644 index 000000000..b3841ba00 --- /dev/null +++ b/kernel/kernel/time/tick-sched.c @@ -0,0 +1,1255 @@ +/* + * linux/kernel/time/tick-sched.c + * + * Copyright(C) 2005-2006, Thomas Gleixner + * 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 +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#include "tick-internal.h" + +#include + +/* + * 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 jiffies_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 jiffies_lock: + */ + delta = ktime_sub(now, last_jiffies_update); + if (delta.tv64 < tick_period.tv64) + return; + + /* Reevalute with jiffies_lock held */ + raw_spin_lock(&jiffies_lock); + write_seqcount_begin(&jiffies_seq); + + 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); + } else { + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); + return; + } + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); + update_wall_time(); +} + +/* + * Initialize and return retrieve the jiffies update. + */ +static ktime_t tick_init_jiffy_update(void) +{ + ktime_t period; + + raw_spin_lock(&jiffies_lock); + write_seqcount_begin(&jiffies_seq); + /* Did we start the jiffies update yet ? */ + if (last_jiffies_update.tv64 == 0) + last_jiffies_update = tick_next_period; + period = last_jiffies_update; + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); + return period; +} + + +static void tick_sched_do_timer(ktime_t now) +{ + int cpu = smp_processor_id(); + +#ifdef CONFIG_NO_HZ_COMMON + /* + * Check if the do_timer duty was dropped. We don't care about + * concurrency: This happens only when the cpu in charge went + * into a long sleep. If two cpus happen to assign themself to + * this duty, then the jiffies update is still serialized by + * jiffies_lock. + */ + if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE) + && !tick_nohz_full_cpu(cpu)) + tick_do_timer_cpu = cpu; +#endif + + /* Check, if the jiffies need an update */ + if (tick_do_timer_cpu == cpu) + tick_do_update_jiffies64(now); +} + +static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) +{ +#ifdef CONFIG_NO_HZ_COMMON + /* + * 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(); + if (is_idle_task(current)) + ts->idle_jiffies++; + } +#endif + update_process_times(user_mode(regs)); + profile_tick(CPU_PROFILING); +} + +#ifdef CONFIG_NO_HZ_FULL +cpumask_var_t tick_nohz_full_mask; +cpumask_var_t housekeeping_mask; +bool tick_nohz_full_running; + +static bool can_stop_full_tick(void) +{ + WARN_ON_ONCE(!irqs_disabled()); + + if (!sched_can_stop_tick()) { + trace_tick_stop(0, "more than 1 task in runqueue\n"); + return false; + } + + if (!posix_cpu_timers_can_stop_tick(current)) { + trace_tick_stop(0, "posix timers running\n"); + return false; + } + + if (!perf_event_can_stop_tick()) { + trace_tick_stop(0, "perf events running\n"); + return false; + } + + if (!arch_irq_work_has_interrupt()) { + trace_tick_stop(0, "missing irq work interrupt\n"); + return false; + } + + /* sched_clock_tick() needs us? */ +#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK + /* + * TODO: kick full dynticks CPUs when + * sched_clock_stable is set. + */ + if (!sched_clock_stable()) { + trace_tick_stop(0, "unstable sched clock\n"); + /* + * Don't allow the user to think they can get + * full NO_HZ with this machine. + */ + WARN_ONCE(tick_nohz_full_running, + "NO_HZ FULL will not work with unstable sched clock"); + return false; + } +#endif + + return true; +} + +static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now); + +/* + * Re-evaluate the need for the tick on the current CPU + * and restart it if necessary. + */ +void __tick_nohz_full_check(void) +{ + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); + + if (tick_nohz_full_cpu(smp_processor_id())) { + if (ts->tick_stopped && !is_idle_task(current)) { + if (!can_stop_full_tick()) + tick_nohz_restart_sched_tick(ts, ktime_get()); + } + } +} + +static void nohz_full_kick_work_func(struct irq_work *work) +{ + __tick_nohz_full_check(); +} + +static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = { + .func = nohz_full_kick_work_func, + .flags = IRQ_WORK_HARD_IRQ, +}; + +/* + * Kick this CPU if it's full dynticks in order to force it to + * re-evaluate its dependency on the tick and restart it if necessary. + * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(), + * is NMI safe. + */ +void tick_nohz_full_kick(void) +{ + if (!tick_nohz_full_cpu(smp_processor_id())) + return; + + irq_work_queue(this_cpu_ptr(&nohz_full_kick_work)); +} + +/* + * Kick the CPU if it's full dynticks in order to force it to + * re-evaluate its dependency on the tick and restart it if necessary. + */ +void tick_nohz_full_kick_cpu(int cpu) +{ + if (!tick_nohz_full_cpu(cpu)) + return; + + irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); +} + +static void nohz_full_kick_ipi(void *info) +{ + __tick_nohz_full_check(); +} + +/* + * Kick all full dynticks CPUs in order to force these to re-evaluate + * their dependency on the tick and restart it if necessary. + */ +void tick_nohz_full_kick_all(void) +{ + if (!tick_nohz_full_running) + return; + + preempt_disable(); + smp_call_function_many(tick_nohz_full_mask, + nohz_full_kick_ipi, NULL, false); + tick_nohz_full_kick(); + preempt_enable(); +} + +/* + * Re-evaluate the need for the tick as we switch the current task. + * It might need the tick due to per task/process properties: + * perf events, posix cpu timers, ... + */ +void __tick_nohz_task_switch(struct task_struct *tsk) +{ + unsigned long flags; + + local_irq_save(flags); + + if (!tick_nohz_full_cpu(smp_processor_id())) + goto out; + + if (tick_nohz_tick_stopped() && !can_stop_full_tick()) + tick_nohz_full_kick(); + +out: + local_irq_restore(flags); +} + +/* Parse the boot-time nohz CPU list from the kernel parameters. */ +static int __init tick_nohz_full_setup(char *str) +{ + alloc_bootmem_cpumask_var(&tick_nohz_full_mask); + if (cpulist_parse(str, tick_nohz_full_mask) < 0) { + pr_warning("NOHZ: Incorrect nohz_full cpumask\n"); + free_bootmem_cpumask_var(tick_nohz_full_mask); + return 1; + } + tick_nohz_full_running = true; + + return 1; +} +__setup("nohz_full=", tick_nohz_full_setup); + +static int tick_nohz_cpu_down_callback(struct notifier_block *nfb, + unsigned long action, + void *hcpu) +{ + unsigned int cpu = (unsigned long)hcpu; + + switch (action & ~CPU_TASKS_FROZEN) { + case CPU_DOWN_PREPARE: + /* + * If we handle the timekeeping duty for full dynticks CPUs, + * we can't safely shutdown that CPU. + */ + if (tick_nohz_full_running && tick_do_timer_cpu == cpu) + return NOTIFY_BAD; + break; + } + return NOTIFY_OK; +} + +static int tick_nohz_init_all(void) +{ + int err = -1; + +#ifdef CONFIG_NO_HZ_FULL_ALL + if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) { + WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n"); + return err; + } + err = 0; + cpumask_setall(tick_nohz_full_mask); + tick_nohz_full_running = true; +#endif + return err; +} + +void __init tick_nohz_init(void) +{ + int cpu; + + if (!tick_nohz_full_running) { + if (tick_nohz_init_all() < 0) + return; + } + + if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) { + WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n"); + cpumask_clear(tick_nohz_full_mask); + tick_nohz_full_running = false; + return; + } + + /* + * Full dynticks uses irq work to drive the tick rescheduling on safe + * locking contexts. But then we need irq work to raise its own + * interrupts to avoid circular dependency on the tick + */ + if (!arch_irq_work_has_interrupt()) { + pr_warning("NO_HZ: Can't run full dynticks because arch doesn't " + "support irq work self-IPIs\n"); + cpumask_clear(tick_nohz_full_mask); + cpumask_copy(housekeeping_mask, cpu_possible_mask); + tick_nohz_full_running = false; + return; + } + + cpu = smp_processor_id(); + + if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { + pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu); + cpumask_clear_cpu(cpu, tick_nohz_full_mask); + } + + cpumask_andnot(housekeeping_mask, + cpu_possible_mask, tick_nohz_full_mask); + + for_each_cpu(cpu, tick_nohz_full_mask) + context_tracking_cpu_set(cpu); + + cpu_notifier(tick_nohz_cpu_down_callback, 0); + pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", + cpumask_pr_args(tick_nohz_full_mask)); +} +#endif + +/* + * NOHZ - aka dynamic tick functionality + */ +#ifdef CONFIG_NO_HZ_COMMON +/* + * NO HZ enabled ? + */ +static int tick_nohz_enabled __read_mostly = 1; +int tick_nohz_active __read_mostly; +/* + * 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); + +int tick_nohz_tick_stopped(void) +{ + return __this_cpu_read(tick_cpu_sched.tick_stopped); +} + +/** + * 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) +{ + unsigned long flags; + + __this_cpu_write(tick_cpu_sched.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(struct tick_sched *ts, ktime_t now) +{ + update_ts_time_stats(smp_processor_id(), ts, now, NULL); + ts->idle_active = 0; + + sched_clock_idle_wakeup_event(0); +} + +static ktime_t tick_nohz_start_idle(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 + * CPU, in microseconds. + * + * This time is measured via accounting rather than sampling, + * and is as accurate as ktime_get() is. + * + * This function returns -1 if NOHZ is not enabled. + */ +u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) +{ + struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + ktime_t now, idle; + + if (!tick_nohz_active) + return -1; + + now = ktime_get(); + if (last_update_time) { + update_ts_time_stats(cpu, ts, now, last_update_time); + idle = ts->idle_sleeptime; + } else { + if (ts->idle_active && !nr_iowait_cpu(cpu)) { + ktime_t delta = ktime_sub(now, ts->idle_entrytime); + + idle = ktime_add(ts->idle_sleeptime, delta); + } else { + idle = ts->idle_sleeptime; + } + } + + return ktime_to_us(idle); + +} +EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); + +/** + * get_cpu_iowait_time_us - get the total iowait 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 iowait time (since boot) for a given + * CPU, in microseconds. + * + * This time is measured via accounting rather than sampling, + * and is as accurate as ktime_get() is. + * + * This function returns -1 if NOHZ is not enabled. + */ +u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) +{ + struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + ktime_t now, iowait; + + if (!tick_nohz_active) + return -1; + + now = ktime_get(); + if (last_update_time) { + update_ts_time_stats(cpu, ts, now, last_update_time); + iowait = ts->iowait_sleeptime; + } else { + if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { + ktime_t delta = ktime_sub(now, ts->idle_entrytime); + + iowait = ktime_add(ts->iowait_sleeptime, delta); + } else { + iowait = ts->iowait_sleeptime; + } + } + + return ktime_to_us(iowait); +} +EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); + +static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, + ktime_t now, int cpu) +{ + unsigned long seq, last_jiffies, next_jiffies, delta_jiffies; + ktime_t last_update, expires, ret = { .tv64 = 0 }; + unsigned long rcu_delta_jiffies; + struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); + u64 time_delta; + + time_delta = timekeeping_max_deferment(); + + /* Read jiffies and the time when jiffies were updated last */ + do { + seq = read_seqcount_begin(&jiffies_seq); + last_update = last_jiffies_update; + last_jiffies = jiffies; + } while (read_seqcount_retry(&jiffies_seq, seq)); + + if (rcu_needs_cpu(&rcu_delta_jiffies) || + arch_needs_cpu() || irq_work_needs_cpu()) { + next_jiffies = last_jiffies + 1; + delta_jiffies = 1; + } else { + /* Get the next timer wheel timer */ + next_jiffies = get_next_timer_interrupt(last_jiffies); + delta_jiffies = next_jiffies - last_jiffies; + if (rcu_delta_jiffies < delta_jiffies) { + next_jiffies = last_jiffies + rcu_delta_jiffies; + delta_jiffies = rcu_delta_jiffies; + } + } + + /* + * Do not stop the tick, if we are only one off (or less) + * or if the cpu is required for RCU: + */ + if (!ts->tick_stopped && delta_jiffies <= 1) + goto out; + + /* Schedule the tick, if we are at least one jiffie off */ + if ((long)delta_jiffies >= 1) { + + /* + * If this cpu is the one which updates jiffies, then + * give up the assignment and let it be taken by the + * cpu which runs the tick timer next, which might be + * this cpu as well. If we don't drop this here the + * jiffies might be stale and do_timer() never + * invoked. Keep track of the fact that it was the one + * which had the do_timer() duty last. If this cpu is + * the one which had the do_timer() duty last, we + * limit the sleep time to the timekeeping + * max_deferement value which we retrieved + * above. Otherwise we can sleep as long as we want. + */ + if (cpu == tick_do_timer_cpu) { + tick_do_timer_cpu = TICK_DO_TIMER_NONE; + ts->do_timer_last = 1; + } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { + time_delta = KTIME_MAX; + ts->do_timer_last = 0; + } else if (!ts->do_timer_last) { + time_delta = KTIME_MAX; + } + +#ifdef CONFIG_NO_HZ_FULL + if (!ts->inidle) { + time_delta = min(time_delta, + scheduler_tick_max_deferment()); + } +#endif + + /* + * calculate the expiry time for the next timer wheel + * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals + * that there is no timer pending or at least extremely + * far into the future (12 days for HZ=1000). In this + * case we set the expiry to the end of time. + */ + if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) { + /* + * Calculate the time delta for the next timer event. + * If the time delta exceeds the maximum time delta + * permitted by the current clocksource then adjust + * the time delta accordingly to ensure the + * clocksource does not wrap. + */ + time_delta = min_t(u64, time_delta, + tick_period.tv64 * delta_jiffies); + } + + if (time_delta < KTIME_MAX) + expires = ktime_add_ns(last_update, time_delta); + else + expires.tv64 = KTIME_MAX; + + /* Skip reprogram of event if its not changed */ + if (ts->tick_stopped && ktime_equal(expires, dev->next_event)) + goto out; + + ret = expires; + + /* + * 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) { + nohz_balance_enter_idle(cpu); + calc_load_enter_idle(); + + ts->last_tick = hrtimer_get_expires(&ts->sched_timer); + ts->tick_stopped = 1; + trace_tick_stop(1, " "); + } + + /* + * If the expiration time == KTIME_MAX, then + * in this case we simply stop the tick timer. + */ + if (unlikely(expires.tv64 == KTIME_MAX)) { + if (ts->nohz_mode == NOHZ_MODE_HIGHRES) + hrtimer_cancel(&ts->sched_timer); + goto out; + } + + if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { + hrtimer_start(&ts->sched_timer, expires, + HRTIMER_MODE_ABS_PINNED); + /* 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()); + } + raise_softirq_irqoff(TIMER_SOFTIRQ); +out: + ts->next_jiffies = next_jiffies; + ts->last_jiffies = last_jiffies; + ts->sleep_length = ktime_sub(dev->next_event, now); + + return ret; +} + +static void tick_nohz_full_stop_tick(struct tick_sched *ts) +{ +#ifdef CONFIG_NO_HZ_FULL + int cpu = smp_processor_id(); + + if (!tick_nohz_full_cpu(cpu) || is_idle_task(current)) + return; + + if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) + return; + + if (!can_stop_full_tick()) + return; + + tick_nohz_stop_sched_tick(ts, ktime_get(), cpu); +#endif +} + +static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) +{ + /* + * If this cpu is offline and it is the one which updates + * jiffies, then give up the assignment and let it be taken by + * the cpu which runs the tick timer next. If we don't drop + * this here the jiffies might be stale and do_timer() never + * invoked. + */ + if (unlikely(!cpu_online(cpu))) { + if (cpu == tick_do_timer_cpu) + tick_do_timer_cpu = TICK_DO_TIMER_NONE; + return false; + } + + if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) { + ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ }; + return false; + } + + if (need_resched()) + return false; + + if (unlikely(local_softirq_pending() && cpu_online(cpu))) { + softirq_check_pending_idle(); + return false; + } + + if (tick_nohz_full_enabled()) { + /* + * Keep the tick alive to guarantee timekeeping progression + * if there are full dynticks CPUs around + */ + if (tick_do_timer_cpu == cpu) + return false; + /* + * Boot safety: make sure the timekeeping duty has been + * assigned before entering dyntick-idle mode, + */ + if (tick_do_timer_cpu == TICK_DO_TIMER_NONE) + return false; + } + + return true; +} + +static void __tick_nohz_idle_enter(struct tick_sched *ts) +{ + ktime_t now, expires; + int cpu = smp_processor_id(); + + now = tick_nohz_start_idle(ts); + + if (can_stop_idle_tick(cpu, ts)) { + int was_stopped = ts->tick_stopped; + + ts->idle_calls++; + + expires = tick_nohz_stop_sched_tick(ts, now, cpu); + if (expires.tv64 > 0LL) { + ts->idle_sleeps++; + ts->idle_expires = expires; + } + + if (!was_stopped && ts->tick_stopped) + ts->idle_jiffies = ts->last_jiffies; + } +} + +/** + * tick_nohz_idle_enter - 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 when we start the idle loop. + * + * The arch is responsible of calling: + * + * - rcu_idle_enter() after its last use of RCU before the CPU is put + * to sleep. + * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. + */ +void tick_nohz_idle_enter(void) +{ + struct tick_sched *ts; + + WARN_ON_ONCE(irqs_disabled()); + + /* + * Update the idle state in the scheduler domain hierarchy + * when tick_nohz_stop_sched_tick() is called from the idle loop. + * State will be updated to busy during the first busy tick after + * exiting idle. + */ + set_cpu_sd_state_idle(); + + local_irq_disable(); + + ts = this_cpu_ptr(&tick_cpu_sched); + ts->inidle = 1; + __tick_nohz_idle_enter(ts); + + local_irq_enable(); +} + +/** + * tick_nohz_irq_exit - update next tick event from interrupt exit + * + * When an interrupt fires while we are idle and it doesn't cause + * a reschedule, it may still add, modify or delete a timer, enqueue + * an RCU callback, etc... + * So we need to re-calculate and reprogram the next tick event. + */ +void tick_nohz_irq_exit(void) +{ + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); + + if (ts->inidle) + __tick_nohz_idle_enter(ts); + else + tick_nohz_full_stop_tick(ts); +} + +/** + * tick_nohz_get_sleep_length - return the length of the current sleep + * + * Called from power state control code with interrupts disabled + */ +ktime_t tick_nohz_get_sleep_length(void) +{ + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); + + return ts->sleep_length; +} + +static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) +{ + hrtimer_cancel(&ts->sched_timer); + hrtimer_set_expires(&ts->sched_timer, ts->last_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_expires(&ts->sched_timer, + HRTIMER_MODE_ABS_PINNED); + /* Check, if the timer was already in the past */ + if (hrtimer_active(&ts->sched_timer)) + break; + } else { + if (!tick_program_event( + hrtimer_get_expires(&ts->sched_timer), 0)) + break; + } + /* Reread time and update jiffies */ + now = ktime_get(); + tick_do_update_jiffies64(now); + } +} + +static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) +{ + /* Update jiffies first */ + tick_do_update_jiffies64(now); + update_cpu_load_nohz(); + + calc_load_exit_idle(); + touch_softlockup_watchdog(); + /* + * Cancel the scheduled timer and restore the tick + */ + ts->tick_stopped = 0; + ts->idle_exittime = now; + + tick_nohz_restart(ts, now); +} + +static void tick_nohz_account_idle_ticks(struct tick_sched *ts) +{ +#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE + unsigned long ticks; + + if (vtime_accounting_enabled()) + return; + /* + * 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) + account_idle_ticks(ticks); +#endif +} + +/** + * tick_nohz_idle_exit - restart the idle tick from the idle task + * + * Restart the idle tick when the CPU is woken up from idle + * This also exit the RCU extended quiescent state. The CPU + * can use RCU again after this function is called. + */ +void tick_nohz_idle_exit(void) +{ + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); + ktime_t now; + + local_irq_disable(); + + WARN_ON_ONCE(!ts->inidle); + + ts->inidle = 0; + + if (ts->idle_active || ts->tick_stopped) + now = ktime_get(); + + if (ts->idle_active) + tick_nohz_stop_idle(ts, now); + + if (ts->tick_stopped) { + tick_nohz_restart_sched_tick(ts, now); + tick_nohz_account_idle_ticks(ts); + } + + 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(hrtimer_get_expires(&ts->sched_timer), 0); +} + +/* + * The nohz low res interrupt handler + */ +static void tick_nohz_handler(struct clock_event_device *dev) +{ + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); + struct pt_regs *regs = get_irq_regs(); + ktime_t now = ktime_get(); + + dev->next_event.tv64 = KTIME_MAX; + + tick_sched_do_timer(now); + tick_sched_handle(ts, regs); + + /* No need to reprogram if we are running tickless */ + if (unlikely(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 = this_cpu_ptr(&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; + } + tick_nohz_active = 1; + 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 (;;) { + hrtimer_set_expires(&ts->sched_timer, next); + if (!tick_program_event(next, 0)) + break; + next = ktime_add(next, tick_period); + } + local_irq_enable(); +} + +/* + * When NOHZ is enabled and the tick is stopped, we need to kick the + * tick timer from irq_enter() so that the jiffies update is kept + * alive during long running softirqs. That's ugly as hell, but + * correctness is key even if we need to fix the offending softirq in + * the first place. + * + * Note, this is different to tick_nohz_restart. We just kick the + * timer and do not touch the other magic bits which need to be done + * when idle is left. + */ +static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now) +{ +#if 0 + /* Switch back to 2.6.27 behaviour */ + ktime_t delta; + + /* + * Do not touch the tick device, when the next expiry is either + * already reached or less/equal than the tick period. + */ + delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); + if (delta.tv64 <= tick_period.tv64) + return; + + tick_nohz_restart(ts, now); +#endif +} + +static inline void tick_nohz_irq_enter(void) +{ + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); + ktime_t now; + + if (!ts->idle_active && !ts->tick_stopped) + return; + now = ktime_get(); + if (ts->idle_active) + tick_nohz_stop_idle(ts, now); + if (ts->tick_stopped) { + tick_nohz_update_jiffies(now); + tick_nohz_kick_tick(ts, now); + } +} + +#else + +static inline void tick_nohz_switch_to_nohz(void) { } +static inline void tick_nohz_irq_enter(void) { } + +#endif /* CONFIG_NO_HZ_COMMON */ + +/* + * Called from irq_enter to notify about the possible interruption of idle() + */ +void tick_irq_enter(void) +{ + tick_check_oneshot_broadcast_this_cpu(); + tick_nohz_irq_enter(); +} + +/* + * 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. + */ +static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) +{ + struct tick_sched *ts = + container_of(timer, struct tick_sched, sched_timer); + struct pt_regs *regs = get_irq_regs(); + ktime_t now = ktime_get(); + + tick_sched_do_timer(now); + + /* + * Do not call, when we are not in irq context and have + * no valid regs pointer + */ + if (regs) + tick_sched_handle(ts, regs); + + /* No need to reprogram if we are in idle or full dynticks mode */ + if (unlikely(ts->tick_stopped)) + return HRTIMER_NORESTART; + + hrtimer_forward(timer, now, tick_period); + + return HRTIMER_RESTART; +} + +static int sched_skew_tick; + +static int __init skew_tick(char *str) +{ + get_option(&str, &sched_skew_tick); + + return 0; +} +early_param("skew_tick", skew_tick); + +/** + * tick_setup_sched_timer - setup the tick emulation timer + */ +void tick_setup_sched_timer(void) +{ + struct tick_sched *ts = this_cpu_ptr(&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.irqsafe = 1; + ts->sched_timer.function = tick_sched_timer; + + /* Get the next period (per cpu) */ + hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); + + /* Offset the tick to avert jiffies_lock contention. */ + if (sched_skew_tick) { + u64 offset = ktime_to_ns(tick_period) >> 1; + do_div(offset, num_possible_cpus()); + offset *= smp_processor_id(); + hrtimer_add_expires_ns(&ts->sched_timer, offset); + } + + for (;;) { + hrtimer_forward(&ts->sched_timer, now, tick_period); + hrtimer_start_expires(&ts->sched_timer, + HRTIMER_MODE_ABS_PINNED); + /* Check, if the timer was already in the past */ + if (hrtimer_active(&ts->sched_timer)) + break; + now = ktime_get(); + } + +#ifdef CONFIG_NO_HZ_COMMON + if (tick_nohz_enabled) { + ts->nohz_mode = NOHZ_MODE_HIGHRES; + tick_nohz_active = 1; + } +#endif +} +#endif /* HIGH_RES_TIMERS */ + +#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS +void tick_cancel_sched_timer(int cpu) +{ + struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + +# ifdef CONFIG_HIGH_RES_TIMERS + if (ts->sched_timer.base) + hrtimer_cancel(&ts->sched_timer); +# endif + + memset(ts, 0, sizeof(*ts)); +} +#endif + +/** + * 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 = this_cpu_ptr(&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 = this_cpu_ptr(&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_valid_for_hres() || !tick_is_oneshot_available()) + return 0; + + if (!allow_nohz) + return 1; + + tick_nohz_switch_to_nohz(); + return 0; +}