clockevents: broadcast fixup possible waiters
Thomas Gleixner [Sat, 6 Sep 2008 01:01:45 +0000 (03:01 +0200)]
Until the C1E patches arrived there where no users of periodic broadcast
before switching to oneshot mode. Now we need to trigger a possible
waiter for a periodic broadcast when switching to oneshot mode.
Otherwise we can starve them for ever.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/time/tick-broadcast.c

index 2bc1f04..2f5a382 100644 (file)
@@ -491,6 +491,18 @@ static void tick_broadcast_clear_oneshot(int cpu)
        cpu_clear(cpu, tick_broadcast_oneshot_mask);
 }
 
+static void tick_broadcast_init_next_event(cpumask_t *mask, ktime_t expires)
+{
+       struct tick_device *td;
+       int cpu;
+
+       for_each_cpu_mask_nr(cpu, *mask) {
+               td = &per_cpu(tick_cpu_device, cpu);
+               if (td->evtdev)
+                       td->evtdev->next_event = expires;
+       }
+}
+
 /**
  * tick_broadcast_setup_oneshot - setup the broadcast device
  */
@@ -498,9 +510,32 @@ void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
 {
        /* Set it up only once ! */
        if (bc->event_handler != tick_handle_oneshot_broadcast) {
+               int was_periodic = bc->mode == CLOCK_EVT_MODE_PERIODIC;
+               int cpu = smp_processor_id();
+               cpumask_t mask;
+
                bc->event_handler = tick_handle_oneshot_broadcast;
                clockevents_set_mode(bc, CLOCK_EVT_MODE_ONESHOT);
-               bc->next_event.tv64 = KTIME_MAX;
+
+               /* Take the do_timer update */
+               tick_do_timer_cpu = cpu;
+
+               /*
+                * 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.
+                */
+               mask = tick_broadcast_mask;
+               cpu_clear(cpu, mask);
+               cpus_or(tick_broadcast_oneshot_mask,
+                       tick_broadcast_oneshot_mask, mask);
+
+               if (was_periodic && !cpus_empty(mask)) {
+                       tick_broadcast_init_next_event(&mask, tick_next_period);
+                       tick_broadcast_set_event(tick_next_period, 1);
+               } else
+                       bc->next_event.tv64 = KTIME_MAX;
        }
 }