// SPDX-License-Identifier: GPL-2.0 /* * This file contains functions which emulate a local clock-event * device via a broadcast event source. * * Copyright(C) 2005-2006, Thomas Gleixner * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner */ #include #include #include #include #include #include #include #include #include #include "tick-internal.h" /* * Broadcast support for broken x86 hardware, where the local apic * timer stops in C3 state. */ static struct tick_device tick_broadcast_device; static cpumask_var_t tick_broadcast_mask __cpumask_var_read_mostly; static cpumask_var_t tick_broadcast_on __cpumask_var_read_mostly; static cpumask_var_t tmpmask __cpumask_var_read_mostly; static int tick_broadcast_forced; static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(tick_broadcast_lock); #ifdef CONFIG_TICK_ONESHOT static DEFINE_PER_CPU(struct clock_event_device *, tick_oneshot_wakeup_device); static void tick_broadcast_setup_oneshot(struct clock_event_device *bc, bool from_periodic); static void tick_broadcast_clear_oneshot(int cpu); static void tick_resume_broadcast_oneshot(struct clock_event_device *bc); # ifdef CONFIG_HOTPLUG_CPU static void tick_broadcast_oneshot_offline(unsigned int cpu); # endif #else static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc, bool from_periodic) { BUG(); } static inline void tick_broadcast_clear_oneshot(int cpu) { } static inline void tick_resume_broadcast_oneshot(struct clock_event_device *bc) { } # ifdef CONFIG_HOTPLUG_CPU static inline void tick_broadcast_oneshot_offline(unsigned int cpu) { } # endif #endif /* * Debugging: see timer_list.c */ struct tick_device *tick_get_broadcast_device(void) { return &tick_broadcast_device; } struct cpumask *tick_get_broadcast_mask(void) { return tick_broadcast_mask; } static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu); const struct clock_event_device *tick_get_wakeup_device(int cpu) { return tick_get_oneshot_wakeup_device(cpu); } /* * Start the device in periodic mode */ static void tick_broadcast_start_periodic(struct clock_event_device *bc) { if (bc) tick_setup_periodic(bc, 1); } /* * Check, if the device can be utilized as broadcast device: */ static bool tick_check_broadcast_device(struct clock_event_device *curdev, struct clock_event_device *newdev) { if ((newdev->features & CLOCK_EVT_FEAT_DUMMY) || (newdev->features & CLOCK_EVT_FEAT_PERCPU) || (newdev->features & CLOCK_EVT_FEAT_C3STOP)) return false; if (tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT && !(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) return false; return !curdev || newdev->rating > curdev->rating; } #ifdef CONFIG_TICK_ONESHOT static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu) { return per_cpu(tick_oneshot_wakeup_device, cpu); } static void tick_oneshot_wakeup_handler(struct clock_event_device *wd) { /* * If we woke up early and the tick was reprogrammed in the * meantime then this may be spurious but harmless. */ tick_receive_broadcast(); } static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev, int cpu) { struct clock_event_device *curdev = tick_get_oneshot_wakeup_device(cpu); if (!newdev) goto set_device; if ((newdev->features & CLOCK_EVT_FEAT_DUMMY) || (newdev->features & CLOCK_EVT_FEAT_C3STOP)) return false; if (!(newdev->features & CLOCK_EVT_FEAT_PERCPU) || !(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) return false; if (!cpumask_equal(newdev->cpumask, cpumask_of(cpu))) return false; if (curdev && newdev->rating <= curdev->rating) return false; if (!try_module_get(newdev->owner)) return false; newdev->event_handler = tick_oneshot_wakeup_handler; set_device: clockevents_exchange_device(curdev, newdev); per_cpu(tick_oneshot_wakeup_device, cpu) = newdev; return true; } #else static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu) { return NULL; } static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev, int cpu) { return false; } #endif /* * Conditionally install/replace broadcast device */ void tick_install_broadcast_device(struct clock_event_device *dev, int cpu) { struct clock_event_device *cur = tick_broadcast_device.evtdev; if (tick_set_oneshot_wakeup_device(dev, cpu)) return; if (!tick_check_broadcast_device(cur, dev)) return; if (!try_module_get(dev->owner)) return; clockevents_exchange_device(cur, dev); if (cur) cur->event_handler = clockevents_handle_noop; tick_broadcast_device.evtdev = dev; if (!cpumask_empty(tick_broadcast_mask)) tick_broadcast_start_periodic(dev); if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT)) return; /* * If the system already runs in oneshot mode, switch the newly * registered broadcast device to oneshot mode explicitly. */ if (tick_broadcast_oneshot_active()) { tick_broadcast_switch_to_oneshot(); return; } /* * Inform all cpus about this. We might be in a situation * where we did not switch to oneshot mode because the per cpu * devices are affected by CLOCK_EVT_FEAT_C3STOP and the lack * of a oneshot capable broadcast device. Without that * notification the systems stays stuck in periodic mode * forever. */ tick_clock_notify(); } /* * Check, if the device is the broadcast device */ int tick_is_broadcast_device(struct clock_event_device *dev) { return (dev && tick_broadcast_device.evtdev == dev); } int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq) { int ret = -ENODEV; if (tick_is_broadcast_device(dev)) { raw_spin_lock(&tick_broadcast_lock); ret = __clockevents_update_freq(dev, freq); raw_spin_unlock(&tick_broadcast_lock); } return ret; } static void err_broadcast(const struct cpumask *mask) { pr_crit_once("Failed to broadcast timer tick. Some CPUs may be unresponsive.\n"); } static void tick_device_setup_broadcast_func(struct clock_event_device *dev) { if (!dev->broadcast) dev->broadcast = tick_broadcast; if (!dev->broadcast) { pr_warn_once("%s depends on broadcast, but no broadcast function available\n", dev->name); dev->broadcast = err_broadcast; } } /* * Check, if the device is dysfunctional and a placeholder, which * needs to be handled by the broadcast device. */ int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu) { struct clock_event_device *bc = tick_broadcast_device.evtdev; unsigned long flags; int ret = 0; raw_spin_lock_irqsave(&tick_broadcast_lock, flags); /* * Devices might be registered with both periodic and oneshot * mode disabled. This signals, that the device needs to be * operated from the broadcast device and is a placeholder for * the cpu local device. */ if (!tick_device_is_functional(dev)) { dev->event_handler = tick_handle_periodic; tick_device_setup_broadcast_func(dev); cpumask_set_cpu(cpu, tick_broadcast_mask); if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) tick_broadcast_start_periodic(bc); else tick_broadcast_setup_oneshot(bc, false); ret = 1; } else { /* * Clear the broadcast bit for this cpu if the * device is not power state affected. */ if (!(dev->features & CLOCK_EVT_FEAT_C3STOP)) cpumask_clear_cpu(cpu, tick_broadcast_mask); else tick_device_setup_broadcast_func(dev); /* * Clear the broadcast bit if the CPU is not in * periodic broadcast on state. */ if (!cpumask_test_cpu(cpu, tick_broadcast_on)) cpumask_clear_cpu(cpu, tick_broadcast_mask); switch (tick_broadcast_device.mode) { case TICKDEV_MODE_ONESHOT: /* * If the system is in oneshot mode we can * unconditionally clear the oneshot mask bit, * because the CPU is running and therefore * not in an idle state which causes the power * state affected device to stop. Let the * caller initialize the device. */ tick_broadcast_clear_oneshot(cpu); ret = 0; break; case TICKDEV_MODE_PERIODIC: /* * If the system is in periodic mode, check * whether the broadcast device can be * switched off now. */ if (cpumask_empty(tick_broadcast_mask) && bc) clockevents_shutdown(bc); /* * If we kept the cpu in the broadcast mask, * tell the caller to leave the per cpu device * in shutdown state. The periodic interrupt * is delivered by the broadcast device, if * the broadcast device exists and is not * hrtimer based. */ if (bc && !(bc->features & CLOCK_EVT_FEAT_HRTIMER)) ret = cpumask_test_cpu(cpu, tick_broadcast_mask); break; default: break; } } raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); return ret; } int tick_receive_broadcast(void) { struct tick_device *td = this_cpu_ptr(&tick_cpu_device); struct clock_event_device *evt = td->evtdev; if (!evt) return -ENODEV; if (!evt->event_handler) return -EINVAL; evt->event_handler(evt); return 0; } /* * Broadcast the event to the cpus, which are set in the mask (mangled). */ static bool tick_do_broadcast(struct cpumask *mask) { int cpu = smp_processor_id(); struct tick_device *td; bool local = false; /* * Check, if the current cpu is in the mask */ if (cpumask_test_cpu(cpu, mask)) { struct clock_event_device *bc = tick_broadcast_device.evtdev; cpumask_clear_cpu(cpu, mask); /* * We only run the local handler, if the broadcast * device is not hrtimer based. Otherwise we run into * a hrtimer recursion. * * local timer_interrupt() * local_handler() * expire_hrtimers() * bc_handler() * local_handler() * expire_hrtimers() */ local = !(bc->features & CLOCK_EVT_FEAT_HRTIMER); } if (!cpumask_empty(mask)) { /* * It might be necessary to actually check whether the devices * have different broadcast functions. For now, just use the * one of the first device. This works as long as we have this * misfeature only on x86 (lapic) */ td = &per_cpu(tick_cpu_device, cpumask_first(mask)); td->evtdev->broadcast(mask); } return local; } /* * Periodic broadcast: * - invoke the broadcast handlers */ static bool tick_do_periodic_broadcast(void) { cpumask_and(tmpmask, cpu_online_mask, tick_broadcast_mask); return tick_do_broadcast(tmpmask); } /* * Event handler for periodic broadcast ticks */ static void tick_handle_periodic_broadcast(struct clock_event_device *dev) { struct tick_device *td = this_cpu_ptr(&tick_cpu_device); bool bc_local; raw_spin_lock(&tick_broadcast_lock); /* Handle spurious interrupts gracefully */ if (clockevent_state_shutdown(tick_broadcast_device.evtdev)) { raw_spin_unlock(&tick_broadcast_lock); return; } bc_local = tick_do_periodic_broadcast(); if (clockevent_state_oneshot(dev)) { ktime_t next = ktime_add_ns(dev->next_event, TICK_NSEC); clockevents_program_event(dev, next, true); } raw_spin_unlock(&tick_broadcast_lock); /* * We run the handler of the local cpu after dropping * tick_broadcast_lock because the handler might deadlock when * trying to switch to oneshot mode. */ if (bc_local) td->evtdev->event_handler(td->evtdev); } /** * tick_broadcast_control - Enable/disable or force broadcast mode * @mode: The selected broadcast mode * * Called when the system enters a state where affected tick devices * might stop. Note: TICK_BROADCAST_FORCE cannot be undone. */ void tick_broadcast_control(enum tick_broadcast_mode mode) { struct clock_event_device *bc, *dev; struct tick_device *td; int cpu, bc_stopped; unsigned long flags; /* Protects also the local clockevent device. */ raw_spin_lock_irqsave(&tick_broadcast_lock, flags); td = this_cpu_ptr(&tick_cpu_device); dev = td->evtdev; /* * Is the device not affected by the powerstate ? */ if (!dev || !(dev->features & CLOCK_EVT_FEAT_C3STOP)) goto out; if (!tick_device_is_functional(dev)) goto out; cpu = smp_processor_id(); bc = tick_broadcast_device.evtdev; bc_stopped = cpumask_empty(tick_broadcast_mask); switch (mode) { case TICK_BROADCAST_FORCE: tick_broadcast_forced = 1; fallthrough; case TICK_BROADCAST_ON: cpumask_set_cpu(cpu, tick_broadcast_on); if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_mask)) { /* * Only shutdown the cpu local device, if: * * - the broadcast device exists * - the broadcast device is not a hrtimer based one * - the broadcast device is in periodic mode to * avoid a hiccup during switch to oneshot mode */ if (bc && !(bc->features & CLOCK_EVT_FEAT_HRTIMER) && tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) clockevents_shutdown(dev); } break; case TICK_BROADCAST_OFF: if (tick_broadcast_forced) break; cpumask_clear_cpu(cpu, tick_broadcast_on); if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_mask)) { if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) tick_setup_periodic(dev, 0); } break; } if (bc) { if (cpumask_empty(tick_broadcast_mask)) { if (!bc_stopped) clockevents_shutdown(bc); } else if (bc_stopped) { if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) tick_broadcast_start_periodic(bc); else tick_broadcast_setup_oneshot(bc, false); } } out: raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); } EXPORT_SYMBOL_GPL(tick_broadcast_control); /* * Set the periodic handler depending on broadcast on/off */ void tick_set_periodic_handler(struct clock_event_device *dev, int broadcast) { if (!broadcast) dev->event_handler = tick_handle_periodic; else dev->event_handler = tick_handle_periodic_broadcast; } #ifdef CONFIG_HOTPLUG_CPU static void tick_shutdown_broadcast(void) { struct clock_event_device *bc = tick_broadcast_device.evtdev; if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) { if (bc && cpumask_empty(tick_broadcast_mask)) clockevents_shutdown(bc); } } /* * Remove a CPU from broadcasting */ void tick_broadcast_offline(unsigned int cpu) { raw_spin_lock(&tick_broadcast_lock); cpumask_clear_cpu(cpu, tick_broadcast_mask); cpumask_clear_cpu(cpu, tick_broadcast_on); tick_broadcast_oneshot_offline(cpu); tick_shutdown_broadcast(); raw_spin_unlock(&tick_broadcast_lock); } #endif void tick_suspend_broadcast(void) { struct clock_event_device *bc; unsigned long flags; raw_spin_lock_irqsave(&tick_broadcast_lock, flags); bc = tick_broadcast_device.evtdev; if (bc) clockevents_shutdown(bc); raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); } /* * This is called from tick_resume_local() on a resuming CPU. That's * called from the core resume function, tick_unfreeze() and the magic XEN * resume hackery. * * In none of these cases the broadcast device mode can change and the * bit of the resuming CPU in the broadcast mask is safe as well. */ bool tick_resume_check_broadcast(void) { if (tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT) return false; else return cpumask_test_cpu(smp_processor_id(), tick_broadcast_mask); } void tick_resume_broadcast(void) { struct clock_event_device *bc; unsigned long flags; raw_spin_lock_irqsave(&tick_broadcast_lock, flags); bc = tick_broadcast_device.evtdev; if (bc) { clockevents_tick_resume(bc); switch (tick_broadcast_device.mode) { case TICKDEV_MODE_PERIODIC: if (!cpumask_empty(tick_broadcast_mask)) tick_broadcast_start_periodic(bc); break; case TICKDEV_MODE_ONESHOT: if (!cpumask_empty(tick_broadcast_mask)) tick_resume_broadcast_oneshot(bc); break; } } raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); } #ifdef CONFIG_TICK_ONESHOT static cpumask_var_t tick_broadcast_oneshot_mask __cpumask_var_read_mostly; static cpumask_var_t tick_broadcast_pending_mask __cpumask_var_read_mostly; static cpumask_var_t tick_broadcast_force_mask __cpumask_var_read_mostly; /* * Exposed for debugging: see timer_list.c */ struct cpumask *tick_get_broadcast_oneshot_mask(void) { return tick_broadcast_oneshot_mask; } /* * Called before going idle with interrupts disabled. Checks whether a * broadcast event from the other core is about to happen. We detected * that in tick_broadcast_oneshot_control(). The callsite can use this * to avoid a deep idle transition as we are about to get the * broadcast IPI right away. */ noinstr int tick_check_broadcast_expired(void) { #ifdef _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H return arch_test_bit(smp_processor_id(), cpumask_bits(tick_broadcast_force_mask)); #else return cpumask_test_cpu(smp_processor_id(), tick_broadcast_force_mask); #endif } /* * Set broadcast interrupt affinity */ static void tick_broadcast_set_affinity(struct clock_event_device *bc, const struct cpumask *cpumask) { if (!(bc->features & CLOCK_EVT_FEAT_DYNIRQ)) return; if (cpumask_equal(bc->cpumask, cpumask)) return; bc->cpumask = cpumask; irq_set_affinity(bc->irq, bc->cpumask); } static void tick_broadcast_set_event(struct clock_event_device *bc, int cpu, ktime_t expires) { if (!clockevent_state_oneshot(bc)) clockevents_switch_state(bc, CLOCK_EVT_STATE_ONESHOT); clockevents_program_event(bc, expires, 1); tick_broadcast_set_affinity(bc, cpumask_of(cpu)); } static void tick_resume_broadcast_oneshot(struct clock_event_device *bc) { clockevents_switch_state(bc, CLOCK_EVT_STATE_ONESHOT); } /* * Called from irq_enter() when idle was interrupted to reenable the * per cpu device. */ void tick_check_oneshot_broadcast_this_cpu(void) { if (cpumask_test_cpu(smp_processor_id(), tick_broadcast_oneshot_mask)) { struct tick_device *td = this_cpu_ptr(&tick_cpu_device); /* * We might be in the middle of switching over from * periodic to oneshot. If the CPU has not yet * switched over, leave the device alone. */ if (td->mode == TICKDEV_MODE_ONESHOT) { clockevents_switch_state(td->evtdev, CLOCK_EVT_STATE_ONESHOT); } } } /* * Handle oneshot mode broadcasting */ static void tick_handle_oneshot_broadcast(struct clock_event_device *dev) { struct tick_device *td; ktime_t now, next_event; int cpu, next_cpu = 0; bool bc_local; raw_spin_lock(&tick_broadcast_lock); dev->next_event = KTIME_MAX; next_event = KTIME_MAX; cpumask_clear(tmpmask); now = ktime_get(); /* Find all expired events */ for_each_cpu(cpu, tick_broadcast_oneshot_mask) { /* * Required for !SMP because for_each_cpu() reports * unconditionally CPU0 as set on UP kernels. */ if (!IS_ENABLED(CONFIG_SMP) && cpumask_empty(tick_broadcast_oneshot_mask)) break; td = &per_cpu(tick_cpu_device, cpu); if (td->evtdev->next_event <= now) { cpumask_set_cpu(cpu, tmpmask); /* * Mark the remote cpu in the pending mask, so * it can avoid reprogramming the cpu local * timer in tick_broadcast_oneshot_control(). */ cpumask_set_cpu(cpu, tick_broadcast_pending_mask); } else if (td->evtdev->next_event < next_event) { next_event = td->evtdev->next_event; next_cpu = cpu; } } /* * Remove the current cpu from the pending mask. The event is * delivered immediately in tick_do_broadcast() ! */ cpumask_clear_cpu(smp_processor_id(), tick_broadcast_pending_mask); /* Take care of enforced broadcast requests */ cpumask_or(tmpmask, tmpmask, tick_broadcast_force_mask); cpumask_clear(tick_broadcast_force_mask); /* * Sanity check. Catch the case where we try to broadcast to * offline cpus. */ if (WARN_ON_ONCE(!cpumask_subset(tmpmask, cpu_online_mask))) cpumask_and(tmpmask, tmpmask, cpu_online_mask); /* * Wakeup the cpus which have an expired event. */ bc_local = tick_do_broadcast(tmpmask); /* * Two reasons for reprogram: * * - The global event did not expire any CPU local * events. This happens in dyntick mode, as the maximum PIT * delta is quite small. * * - There are pending events on sleeping CPUs which were not * in the event mask */ if (next_event != KTIME_MAX) tick_broadcast_set_event(dev, next_cpu, next_event); raw_spin_unlock(&tick_broadcast_lock); if (bc_local) { td = this_cpu_ptr(&tick_cpu_device); td->evtdev->event_handler(td->evtdev); } } static int broadcast_needs_cpu(struct clock_event_device *bc, int cpu) { if (!(bc->features & CLOCK_EVT_FEAT_HRTIMER)) return 0; if (bc->next_event == KTIME_MAX) return 0; return bc->bound_on == cpu ? -EBUSY : 0; } static void broadcast_shutdown_local(struct clock_event_device *bc, struct clock_event_device *dev) { /* * For hrtimer based broadcasting we cannot shutdown the cpu * local device if our own event is the first one to expire or * if we own the broadcast timer. */ if (bc->features & CLOCK_EVT_FEAT_HRTIMER) { if (broadcast_needs_cpu(bc, smp_processor_id())) return; if (dev->next_event < bc->next_event) return; } clockevents_switch_state(dev, CLOCK_EVT_STATE_SHUTDOWN); } static int ___tick_broadcast_oneshot_control(enum tick_broadcast_state state, struct tick_device *td, int cpu) { struct clock_event_device *bc, *dev = td->evtdev; int ret = 0; ktime_t now; raw_spin_lock(&tick_broadcast_lock); bc = tick_broadcast_device.evtdev; if (state == TICK_BROADCAST_ENTER) { /* * If the current CPU owns the hrtimer broadcast * mechanism, it cannot go deep idle and we do not add * the CPU to the broadcast mask. We don't have to go * through the EXIT path as the local timer is not * shutdown. */ ret = broadcast_needs_cpu(bc, cpu); if (ret) goto out; /* * If the broadcast device is in periodic mode, we * return. */ if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) { /* If it is a hrtimer based broadcast, return busy */ if (bc->features & CLOCK_EVT_FEAT_HRTIMER) ret = -EBUSY; goto out; } if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_oneshot_mask)) { WARN_ON_ONCE(cpumask_test_cpu(cpu, tick_broadcast_pending_mask)); /* Conditionally shut down the local timer. */ broadcast_shutdown_local(bc, dev); /* * We only reprogram the broadcast timer if we * did not mark ourself in the force mask and * if the cpu local event is earlier than the * broadcast event. If the current CPU is in * the force mask, then we are going to be * woken by the IPI right away; we return * busy, so the CPU does not try to go deep * idle. */ if (cpumask_test_cpu(cpu, tick_broadcast_force_mask)) { ret = -EBUSY; } else if (dev->next_event < bc->next_event) { tick_broadcast_set_event(bc, cpu, dev->next_event); /* * In case of hrtimer broadcasts the * programming might have moved the * timer to this cpu. If yes, remove * us from the broadcast mask and * return busy. */ ret = broadcast_needs_cpu(bc, cpu); if (ret) { cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask); } } } } else { if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_oneshot_mask)) { clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT); /* * The cpu which was handling the broadcast * timer marked this cpu in the broadcast * pending mask and fired the broadcast * IPI. So we are going to handle the expired * event anyway via the broadcast IPI * handler. No need to reprogram the timer * with an already expired event. */ if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_pending_mask)) goto out; /* * Bail out if there is no next event. */ if (dev->next_event == KTIME_MAX) goto out; /* * If the pending bit is not set, then we are * either the CPU handling the broadcast * interrupt or we got woken by something else. * * We are no longer in the broadcast mask, so * if the cpu local expiry time is already * reached, we would reprogram the cpu local * timer with an already expired event. * * This can lead to a ping-pong when we return * to idle and therefore rearm the broadcast * timer before the cpu local timer was able * to fire. This happens because the forced * reprogramming makes sure that the event * will happen in the future and depending on * the min_delta setting this might be far * enough out that the ping-pong starts. * * If the cpu local next_event has expired * then we know that the broadcast timer * next_event has expired as well and * broadcast is about to be handled. So we * avoid reprogramming and enforce that the * broadcast handler, which did not run yet, * will invoke the cpu local handler. * * We cannot call the handler directly from * here, because we might be in a NOHZ phase * and we did not go through the irq_enter() * nohz fixups. */ now = ktime_get(); if (dev->next_event <= now) { cpumask_set_cpu(cpu, tick_broadcast_force_mask); goto out; } /* * We got woken by something else. Reprogram * the cpu local timer device. */ tick_program_event(dev->next_event, 1); } } out: raw_spin_unlock(&tick_broadcast_lock); return ret; } static int tick_oneshot_wakeup_control(enum tick_broadcast_state state, struct tick_device *td, int cpu) { struct clock_event_device *dev, *wd; dev = td->evtdev; if (td->mode != TICKDEV_MODE_ONESHOT) return -EINVAL; wd = tick_get_oneshot_wakeup_device(cpu); if (!wd) return -ENODEV; switch (state) { case TICK_BROADCAST_ENTER: clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT_STOPPED); clockevents_switch_state(wd, CLOCK_EVT_STATE_ONESHOT); clockevents_program_event(wd, dev->next_event, 1); break; case TICK_BROADCAST_EXIT: /* We may have transitioned to oneshot mode while idle */ if (clockevent_get_state(wd) != CLOCK_EVT_STATE_ONESHOT) return -ENODEV; } return 0; } int __tick_broadcast_oneshot_control(enum tick_broadcast_state state) { struct tick_device *td = this_cpu_ptr(&tick_cpu_device); int cpu = smp_processor_id(); if (!tick_oneshot_wakeup_control(state, td, cpu)) return 0; if (tick_broadcast_device.evtdev) return ___tick_broadcast_oneshot_control(state, td, cpu); /* * If there is no broadcast or wakeup device, tell the caller not * to go into deep idle. */ return -EBUSY; } /* * Reset the one shot broadcast for a cpu * * Called with tick_broadcast_lock held */ static void tick_broadcast_clear_oneshot(int cpu) { cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask); cpumask_clear_cpu(cpu, tick_broadcast_pending_mask); } static void tick_broadcast_init_next_event(struct cpumask *mask, ktime_t expires) { struct tick_device *td; int cpu; for_each_cpu(cpu, mask) { td = &per_cpu(tick_cpu_device, cpu); if (td->evtdev) td->evtdev->next_event = expires; } } static inline ktime_t tick_get_next_period(void) { ktime_t next; /* * Protect against concurrent updates (store /load tearing on * 32bit). It does not matter if the time is already in the * past. The broadcast device which is about to be programmed will * fire in any case. */ raw_spin_lock(&jiffies_lock); next = tick_next_period; raw_spin_unlock(&jiffies_lock); return next; } /** * tick_broadcast_setup_oneshot - setup the broadcast device */ static void tick_broadcast_setup_oneshot(struct clock_event_device *bc, bool from_periodic) { int cpu = smp_processor_id(); ktime_t nexttick = 0; if (!bc) return; /* * When the broadcast device was switched to oneshot by the first * CPU handling the NOHZ change, the other CPUs will reach this * code via hrtimer_run_queues() -> tick_check_oneshot_change() * too. Set up the broadcast device only once! */ if (bc->event_handler == tick_handle_oneshot_broadcast) { /* * The CPU which switched from periodic to oneshot mode * set the broadcast oneshot bit for all other CPUs which * are in the general (periodic) broadcast mask to ensure * that CPUs which wait for the periodic broadcast are * woken up. * * Clear the bit for the local CPU as the set bit would * prevent the first tick_broadcast_enter() after this CPU * switched to oneshot state to program the broadcast * device. * * This code can also be reached via tick_broadcast_control(), * but this cannot avoid the tick_broadcast_clear_oneshot() * as that would break the periodic to oneshot transition of * secondary CPUs. But that's harmless as the below only * clears already cleared bits. */ tick_broadcast_clear_oneshot(cpu); return; } bc->event_handler = tick_handle_oneshot_broadcast; bc->next_event = KTIME_MAX; /* * When the tick mode is switched from periodic to oneshot it must * be ensured that CPUs which are waiting for periodic broadcast * get their wake-up at the next tick. This is achieved by ORing * tick_broadcast_mask into tick_broadcast_oneshot_mask. * * For other callers, e.g. broadcast device replacement, * tick_broadcast_oneshot_mask must not be touched as this would * set bits for CPUs which are already NOHZ, but not idle. Their * next tick_broadcast_enter() would observe the bit set and fail * to update the expiry time and the broadcast event device. */ if (from_periodic) { cpumask_copy(tmpmask, tick_broadcast_mask); /* Remove the local CPU as it is obviously not idle */ cpumask_clear_cpu(cpu, tmpmask); cpumask_or(tick_broadcast_oneshot_mask, tick_broadcast_oneshot_mask, tmpmask); /* * Ensure that the oneshot broadcast handler will wake the * CPUs which are still waiting for periodic broadcast. */ nexttick = tick_get_next_period(); tick_broadcast_init_next_event(tmpmask, nexttick); /* * If the underlying broadcast clock event device is * already in oneshot state, then there is nothing to do. * The device was already armed for the next tick * in tick_handle_broadcast_periodic() */ if (clockevent_state_oneshot(bc)) return; } /* * When switching from periodic to oneshot mode arm the broadcast * device for the next tick. * * If the broadcast device has been replaced in oneshot mode and * the oneshot broadcast mask is not empty, then arm it to expire * immediately in order to reevaluate the next expiring timer. * @nexttick is 0 and therefore in the past which will cause the * clockevent code to force an event. * * For both cases the programming can be avoided when the oneshot * broadcast mask is empty. * * tick_broadcast_set_event() implicitly switches the broadcast * device to oneshot state. */ if (!cpumask_empty(tick_broadcast_oneshot_mask)) tick_broadcast_set_event(bc, cpu, nexttick); } /* * Select oneshot operating mode for the broadcast device */ void tick_broadcast_switch_to_oneshot(void) { struct clock_event_device *bc; enum tick_device_mode oldmode; unsigned long flags; raw_spin_lock_irqsave(&tick_broadcast_lock, flags); oldmode = tick_broadcast_device.mode; tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT; bc = tick_broadcast_device.evtdev; if (bc) tick_broadcast_setup_oneshot(bc, oldmode == TICKDEV_MODE_PERIODIC); raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); } #ifdef CONFIG_HOTPLUG_CPU void hotplug_cpu__broadcast_tick_pull(int deadcpu) { struct tick_device *td = this_cpu_ptr(&tick_cpu_device); struct clock_event_device *bc; unsigned long flags; raw_spin_lock_irqsave(&tick_broadcast_lock, flags); bc = tick_broadcast_device.evtdev; if (bc && broadcast_needs_cpu(bc, deadcpu)) { /* * If the broadcast force bit of the current CPU is set, * then the current CPU has not yet reprogrammed the local * timer device to avoid a ping-pong race. See * ___tick_broadcast_oneshot_control(). * * If the broadcast device is hrtimer based then * programming the broadcast event below does not have any * effect because the local clockevent device is not * running and not programmed because the broadcast event * is not earlier than the pending event of the local clock * event device. As a consequence all CPUs waiting for a * broadcast event are stuck forever. * * Detect this condition and reprogram the cpu local timer * device to avoid the starvation. */ if (tick_check_broadcast_expired()) { cpumask_clear_cpu(smp_processor_id(), tick_broadcast_force_mask); tick_program_event(td->evtdev->next_event, 1); } /* This moves the broadcast assignment to this CPU: */ clockevents_program_event(bc, bc->next_event, 1); } raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); } /* * Remove a dying CPU from broadcasting */ static void tick_broadcast_oneshot_offline(unsigned int cpu) { if (tick_get_oneshot_wakeup_device(cpu)) tick_set_oneshot_wakeup_device(NULL, cpu); /* * Clear the broadcast masks for the dead cpu, but do not stop * the broadcast device! */ cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask); cpumask_clear_cpu(cpu, tick_broadcast_pending_mask); cpumask_clear_cpu(cpu, tick_broadcast_force_mask); } #endif /* * Check, whether the broadcast device is in one shot mode */ int tick_broadcast_oneshot_active(void) { return tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT; } /* * Check whether the broadcast device supports oneshot. */ bool tick_broadcast_oneshot_available(void) { struct clock_event_device *bc = tick_broadcast_device.evtdev; return bc ? bc->features & CLOCK_EVT_FEAT_ONESHOT : false; } #else int __tick_broadcast_oneshot_control(enum tick_broadcast_state state) { struct clock_event_device *bc = tick_broadcast_device.evtdev; if (!bc || (bc->features & CLOCK_EVT_FEAT_HRTIMER)) return -EBUSY; return 0; } #endif void __init tick_broadcast_init(void) { zalloc_cpumask_var(&tick_broadcast_mask, GFP_NOWAIT); zalloc_cpumask_var(&tick_broadcast_on, GFP_NOWAIT); zalloc_cpumask_var(&tmpmask, GFP_NOWAIT); #ifdef CONFIG_TICK_ONESHOT zalloc_cpumask_var(&tick_broadcast_oneshot_mask, GFP_NOWAIT); zalloc_cpumask_var(&tick_broadcast_pending_mask, GFP_NOWAIT); zalloc_cpumask_var(&tick_broadcast_force_mask, GFP_NOWAIT); #endif }