diff options
| -rw-r--r-- | kernel/time/tick-broadcast.c | 120 |
1 files changed, 88 insertions, 32 deletions
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c index f7fe6fe36173..0916cc9adb82 100644 --- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -35,14 +35,15 @@ 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); +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) { BUG(); } +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 @@ -264,7 +265,7 @@ int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu) if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) tick_broadcast_start_periodic(bc); else - tick_broadcast_setup_oneshot(bc); + tick_broadcast_setup_oneshot(bc, false); ret = 1; } else { /* @@ -500,7 +501,7 @@ void tick_broadcast_control(enum tick_broadcast_mode mode) if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) tick_broadcast_start_periodic(bc); else - tick_broadcast_setup_oneshot(bc); + tick_broadcast_setup_oneshot(bc, false); } } out: @@ -1016,48 +1017,101 @@ static inline ktime_t tick_get_next_period(void) /** * tick_broadcast_setup_oneshot - setup the broadcast device */ -static void tick_broadcast_setup_oneshot(struct clock_event_device *bc) +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; - /* Set it up only once ! */ - if (bc->event_handler != tick_handle_oneshot_broadcast) { - int was_periodic = clockevent_state_periodic(bc); - - bc->event_handler = tick_handle_oneshot_broadcast; - + /* + * 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) { /* - * We must be careful here. There might be other CPUs - * waiting for periodic broadcast. We need to set the - * oneshot_mask bits for those and program the - * broadcast device to fire. + * 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); + cpumask_or(tick_broadcast_oneshot_mask, tick_broadcast_oneshot_mask, tmpmask); - if (was_periodic && !cpumask_empty(tmpmask)) { - ktime_t nextevt = tick_get_next_period(); + /* + * 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); - clockevents_switch_state(bc, CLOCK_EVT_STATE_ONESHOT); - tick_broadcast_init_next_event(tmpmask, nextevt); - tick_broadcast_set_event(bc, cpu, nextevt); - } else - bc->next_event = KTIME_MAX; - } else { /* - * The first cpu which switches to oneshot mode sets - * the bit for all other cpus which are in the general - * (periodic) broadcast mask. So the bit is set and - * would prevent the first broadcast enter after this - * to program the bc device. + * 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() */ - tick_broadcast_clear_oneshot(cpu); + 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); } /* @@ -1066,14 +1120,16 @@ static void tick_broadcast_setup_oneshot(struct clock_event_device *bc) 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); + tick_broadcast_setup_oneshot(bc, oldmode == TICKDEV_MODE_PERIODIC); raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags); } |