pkt_sched: Check the state of tx_queue in dequeue_skb()

Check in dequeue_skb() the state of tx_queue for requeued skb to save
on locking and re-requeuing, and possibly remove the current check in
qdisc_run(). Based on the idea of Alexander Duyck.

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 1b508bd1c06c5ee1a55a17db44ae4857b57cb0e6..5e7e0bd38fe80a8e82829fad7ce6cccdbc4ba8a1 100644 (file)
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -52,11 +52,21 @@ static inline int dev_requeue_skb(struct sk_buff *skb, struct Qdisc *q)
 
 static inline struct sk_buff *dequeue_skb(struct Qdisc *q)
 {
-       struct sk_buff *skb;
-
-       skb = __skb_dequeue(&q->requeue);
-       if (!skb)
+       struct sk_buff *skb = skb_peek(&q->requeue);
+
+       if (unlikely(skb)) {
+               struct net_device *dev = qdisc_dev(q);
+               struct netdev_queue *txq;
+
+               /* check the reason of requeuing without tx lock first */
+               txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));
+               if (!netif_tx_queue_stopped(txq) && !netif_tx_queue_frozen(txq))
+                       __skb_unlink(skb, &q->requeue);
+               else
+                       skb = NULL;
+       } else {
                skb = q->dequeue(q);
+       }
 
        return skb;
 }