On Thu, 2013-12-19 at 15:14 -0800, Linus Torvalds wrote: > On Thu, Dec 19, 2013 at 10:45 AM, Davidlohr Bueso <davidl...@hp.com> wrote: > > > > - increment the counter at queue_lock() as we always end up calling > > queue_me() which adds the element to the list. Upon any error, > > queue_unlock() is called for housekeeping, for which we decrement > > to mach the increment done in queue_lock(). > > > > - decrement the counter at __unqueue_me() to reflect when an element is > > removed from the queue for wakeup related purposes. > > I still hate this whole separate counter thing. It seems really annoying. > > If re-ordering things didn't work out, then why can't just the counter > we *already* have in the spinlock itself work as the counter? Your > counter update logic seems to basically match when you take the > spinlock anyway. > > The *testing* side doesn't actually care about how many waiters there > are, it only cares about whether there are waiters.
True. > And it can look at > the wait-list for that - but you want to close the race between the > entry actually getting added to the list using this counter. But the > place you increment the new counter is the same place as you take the > spinlock, which does that ticket increment. No? I don't think so. If we rely on this, then we could end up missing to-be-queued tasks that are in the process of acquiring the lock, so waiters could sleep forever. So we need a way of acknowledging that a task is in the process of waiting when concurrently doing wakeups. Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
