kernel: Add method to dequeue from a dlist

Dequeuing from a doubly linked list is similar to removing an item
except that it does not re-initialize the dequeued node.

This comes in handy when sorting a doubly linked list (where the
node gets removed and re-added). In that circumstance, re-initializing
the node is required. Furthermore, the compiler does not always
'understand' this. Thus, when performance is critical, dequeuing
may be preferred to removing.

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>

include/zephyr/sys/dlist.h

@@ -492,6 +492,29 @@ static inline void sys_dlist_insert_at(sys_dlist_t *list, sys_dnode_t *node,
 	}
 }
 
+/**
+ * @brief remove a specific node from a list
+ *
+ * Like :c:func:`sys_dlist_remove()`, this routine removes a specific node
+ * from a list. However, unlike :c:func:`sys_dlist_remove()`, this routine
+ * does not re-initialize the removed node. One significant implication of
+ * this difference is that the function :c:func`sys_dnode_is_linked()` will
+ * not work on a dequeued node.
+ *
+ * The list is implicit from the node. The node must be part of a list.
+ * This and other sys_dlist_*() functions are not thread safe.
+ *
+ * @param node the node to dequeue
+ */
+static inline void sys_dlist_dequeue(sys_dnode_t *node)
+{
+	sys_dnode_t *const prev = node->prev;
+	sys_dnode_t *const next = node->next;
+
+	prev->next = next;
+	next->prev = prev;
+}
+
 /**
  * @brief remove a specific node from a list
  *

kernel/include/priority_q.h

@@ -241,8 +241,8 @@ static ALWAYS_INLINE void z_priq_mq_remove(struct _priq_mq *pq,
 {
 	struct prio_info pos = get_prio_info(thread->base.prio);
 
-	sys_dlist_remove(&thread->base.qnode_dlist);
-	if (sys_dlist_is_empty(&pq->queues[pos.offset_prio])) {
+	sys_dlist_dequeue(&thread->base.qnode_dlist);
+	if (unlikely(sys_dlist_is_empty(&pq->queues[pos.offset_prio]))) {
 		pq->bitmask[pos.idx] &= ~BIT(pos.bit);
 	}
 }