/* * The idle thread. We try to conserve power, while trying to keep * overall latency low. The architecture specific idle is passed * a value to indicate the level of "idleness" of the system. */ void cpu_idle(void) { /* endless idle loop with no priority at all */ while (1) { void (*idle)(void) = pm_idle; #ifdef CONFIG_HOTPLUG_CPU if (cpu_is_offline(smp_processor_id())) cpu_die(); #endif if (!idle) idle = default_idle; tick_nohz_stop_sched_tick(1); while (!need_resched()) idle(); tick_nohz_restart_sched_tick(); preempt_enable_no_resched(); schedule(); preempt_disable(); } }
/* * The idle thread. There's no useful work to be * done, so just try to conserve power and have a * low exit latency (ie sit in a loop waiting for * somebody to say that they'd like to reschedule) */ void cpu_idle(void) { int cpu = smp_processor_id(); /* * If we're the non-boot CPU, nothing set the stack canary up * for us. CPU0 already has it initialized but no harm in * doing it again. This is a good place for updating it, as * we wont ever return from this function (so the invalid * canaries already on the stack wont ever trigger). */ boot_init_stack_canary(); current_thread_info()->status |= TS_POLLING; /* endless idle loop with no priority at all */ while (1) { tick_nohz_stop_sched_tick(1); while (!need_resched()) { check_pgt_cache(); rmb(); if (cpu_is_offline(cpu)) play_dead(); local_touch_nmi(); local_irq_disable(); /* Don't trace irqs off for idle */ stop_critical_timings(); if (cpuidle_idle_call()) pm_idle(); start_critical_timings(); } tick_nohz_restart_sched_tick(); preempt_enable_no_resched(); schedule(); preempt_disable(); } }
void cpu_idle(void) { set_thread_flag(TIF_POLLING_NRFLAG); /* endless idle loop with no priority at all */ while (1) { void (*idle)(void) = pm_idle; if (!idle) idle = default_idle; tick_nohz_stop_sched_tick(1); while (!need_resched()) idle(); tick_nohz_restart_sched_tick(); preempt_enable_no_resched(); schedule(); preempt_disable(); check_pgt_cache(); } }
/* * The idle thread. There's no useful work to be done, so just try to conserve * power and have a low exit latency (ie sit in a loop waiting for somebody to * say that they'd like to reschedule) */ void __noreturn cpu_idle(void) { int cpu; /* CPU is going idle. */ cpu = smp_processor_id(); /* endless idle loop with no priority at all */ while (1) { tick_nohz_stop_sched_tick(1); while (!need_resched() && cpu_online(cpu)) { #ifdef CONFIG_MIPS_MT_SMTC extern void smtc_idle_loop_hook(void); smtc_idle_loop_hook(); #endif if (cpu_wait) { /* Don't trace irqs off for idle */ stop_critical_timings(); (*cpu_wait)(); start_critical_timings(); } } #ifdef CONFIG_HOTPLUG_CPU if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map) && (system_state == SYSTEM_RUNNING || system_state == SYSTEM_BOOTING)) play_dead(); #endif tick_nohz_restart_sched_tick(); preempt_enable_no_resched(); schedule(); preempt_disable(); } }
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 }; struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev; u64 time_delta; /* Read jiffies and the time when jiffies were updated last */ do { seq = read_seqbegin(&xtime_lock); last_update = last_jiffies_update; last_jiffies = jiffies; time_delta = timekeeping_max_deferment(); } while (read_seqretry(&xtime_lock, seq)); if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) || arch_needs_cpu(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; } /* * 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) 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; } /* * 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; } /* * 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; return ret; } 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; } if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) return false; if (need_resched()) return false; if (unlikely(local_softirq_pending() && cpu_online(cpu))) { static int ratelimit; if (ratelimit < 10) { printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", (unsigned int) local_softirq_pending()); ratelimit++; } 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(cpu, 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; } }