#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
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 {
/*
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:
/**
* 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);
}
/*
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);
}