+ * Wait Queue
+ */
+#ifndef HAVE___ADD_WAIT_QUEUE_EXCLUSIVE
+static inline void __add_wait_queue_exclusive(wait_queue_head_t *q,
+ wait_queue_t *wait)
+{
+ wait->flags |= WQ_FLAG_EXCLUSIVE;
+ __add_wait_queue(q, wait);
+}
+#endif /* HAVE___ADD_WAIT_QUEUE_EXCLUSIVE */
+
+/**
+ * wait_queue_t of Linux (version < 2.6.34) is a FIFO list for exclusively
+ * waiting threads, which is not always desirable because all threads will
+ * be waken up again and again, even user only needs a few of them to be
+ * active most time. This is not good for performance because cache can
+ * be polluted by different threads.
+ *
+ * LIFO list can resolve this problem because we always wakeup the most
+ * recent active thread by default.
+ *
+ * NB: please don't call non-exclusive & exclusive wait on the same
+ * waitq if add_wait_queue_exclusive_head is used.
+ */
+#define add_wait_queue_exclusive_head(waitq, link) \
+{ \
+ unsigned long flags; \
+ \
+ spin_lock_irqsave(&((waitq)->lock), flags); \
+ __add_wait_queue_exclusive(waitq, link); \
+ spin_unlock_irqrestore(&((waitq)->lock), flags); \
+}
+
+/*