Dequeue_skb has an additional check, for the first packet that
is requeued, to see if the device has requested xmits after a
interval. This is intended to not affect the fast xmit path, and
have minimal overhead to the slow path. Drivers setting the
restart time should not stop/start their tx queues, and hence
the frozen/stopped check can be avoided.
Signed-off-by: Krishna Kumar <krkumar2@xxxxxxxxxx>
---
net/sched/sch_generic.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)
diff -ruNp org/net/sched/sch_generic.c new/net/sched/sch_generic.c
--- org/net/sched/sch_generic.c 2011-05-04 18:57:06.000000000 +0530
+++ new/net/sched/sch_generic.c 2011-05-04 18:57:09.000000000 +0530
@@ -50,17 +50,30 @@ static inline int dev_requeue_skb(struct
return 0;
}
+/*
+ * This function can return a rare false positive for drivers setting
+ * xmit_restart_jiffies (e.g. virtio-net) when xmit_restart_jiffies is
+ * zero but the device may not be ready. That only leads to the skb
+ * being requeued again.
+ */
+static inline int can_restart_xmit(struct Qdisc *q, struct sk_buff *skb)
+{
+ struct net_device *dev = qdisc_dev(q);
+ struct netdev_queue *txq;
+
+ txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));
+ if (unlikely(txq->xmit_restart_jiffies))
+ return time_after_eq(jiffies, txq->xmit_restart_jiffies);
+ return !netif_tx_queue_frozen_or_stopped(txq);
+}
+
static inline struct sk_buff *dequeue_skb(struct Qdisc *q)
{
struct sk_buff *skb = q->gso_skb;
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_frozen_or_stopped(txq)) {
+ if (can_restart_xmit(q, skb)) {
q->gso_skb = NULL;
q->q.qlen--;
} else
--
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