On Wed, May 07, 2014 at 11:01:34AM -0400, Waiman Long wrote:
> @@ -221,11 +222,37 @@ static inline int trylock_pending(struct qspinlock *lock, u32 *pval)
> */
> for (;;) {
> /*
> - * If we observe any contention; queue.
> + * If we observe that the queue is not empty,
> + * return and be queued.
> */
> - if (val & ~_Q_LOCKED_MASK)
> + if (val & _Q_TAIL_MASK)
> return 0;
>
> + if (val == (_Q_LOCKED_VAL|_Q_PENDING_VAL)) {
> + /*
> + * If both the lock and pending bits are set, we wait
> + * a while to see if that either bit will be cleared.
> + * If that is no change, we return and be queued.
> + */
> + if (!retry)
> + return 0;
> + retry--;
> + cpu_relax();
> + cpu_relax();
> + *pval = val = atomic_read(&lock->val);
> + continue;
> + } else if (val == _Q_PENDING_VAL) {
> + /*
> + * Pending bit is set, but not the lock bit.
> + * Assuming that the pending bit holder is going to
> + * set the lock bit and clear the pending bit soon,
> + * it is better to wait than to exit at this point.
> + */
> + cpu_relax();
> + *pval = val = atomic_read(&lock->val);
> + continue;
> + }
Didn't I give a much saner alternative to this mess last time?
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