On Sat, 26 Jun 2010, Rafael J. Wysocki wrote:
> +void pm_relax(void)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&events_lock, flags);
> + if (events_in_progress) {
> + event_count++;
> + if (!--events_in_progress)
> + wake_up_all(&events_wait_queue);
> + }
> + spin_unlock_irqrestore(&events_lock, flags);
> +}
> +bool pm_get_wakeup_count(unsigned long *count)
> +{
> + bool ret;
> +
> + spin_lock_irq(&events_lock);
> + if (capable(CAP_SYS_ADMIN))
> + events_check_enabled = false;
> +
> + if (events_in_progress) {
> + DEFINE_WAIT(wait);
> +
> + do {
> + prepare_to_wait(&events_wait_queue, &wait,
> + TASK_INTERRUPTIBLE);
> + if (!events_in_progress)
> + break;
> + spin_unlock_irq(&events_lock);
> +
> + schedule();
> +
> + spin_lock_irq(&events_lock);
> + } while (!signal_pending(current));
> + finish_wait(&events_wait_queue, &wait);
> + }
> + *count = event_count;
> + ret = !events_in_progress;
> + spin_unlock_irq(&events_lock);
> + return ret;
> +}
Here's a thought. Presumably pm_relax() will end up getting called a
lot more often than pm_get_wakeup_count(). Instead of using a wait
queue, you could make pm_get_wakeup_count() poll at 100-ms intervals.
The total overhead would be smaller.
Here's another thought. If event_count and events_in_progress were
atomic_t then the new spinlock wouldn't be needed at all. (But you
would need an appropriate pair of memory barriers, to guarantee that
when a writer decrements events_in_progress to 0 and increments
event_count, a reader won't see events_in_progress == 0 without also
seeing the incremented event_count.) Overall, this may not be a
significant improvement.
Alan Stern
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