sched: add head drop fifo queue
This adds an additional queuing strategy, called pfifo_head_drop,
to remove the oldest skb in the case of an overflow within the queue -
the head element - instead of the last skb (tail). To remove the oldest
skb in congested situations is useful for sensor network environments
where newer packets reflect the superior information.
Reviewed-by: Florian Westphal <fw@strlen.de>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
index 69188e8..4b0a6cc 100644
--- a/net/sched/sch_fifo.c
+++ b/net/sched/sch_fifo.c
@@ -43,6 +43,26 @@
return qdisc_reshape_fail(skb, sch);
}
+static int pfifo_tail_enqueue(struct sk_buff *skb, struct Qdisc* sch)
+{
+ struct sk_buff *skb_head;
+ struct fifo_sched_data *q = qdisc_priv(sch);
+
+ if (likely(skb_queue_len(&sch->q) < q->limit))
+ return qdisc_enqueue_tail(skb, sch);
+
+ /* queue full, remove one skb to fulfill the limit */
+ skb_head = qdisc_dequeue_head(sch);
+ sch->bstats.bytes -= qdisc_pkt_len(skb_head);
+ sch->bstats.packets--;
+ sch->qstats.drops++;
+ kfree_skb(skb_head);
+
+ qdisc_enqueue_tail(skb, sch);
+
+ return NET_XMIT_CN;
+}
+
static int fifo_init(struct Qdisc *sch, struct nlattr *opt)
{
struct fifo_sched_data *q = qdisc_priv(sch);
@@ -108,6 +128,20 @@
};
EXPORT_SYMBOL(bfifo_qdisc_ops);
+struct Qdisc_ops pfifo_head_drop_qdisc_ops __read_mostly = {
+ .id = "pfifo_head_drop",
+ .priv_size = sizeof(struct fifo_sched_data),
+ .enqueue = pfifo_tail_enqueue,
+ .dequeue = qdisc_dequeue_head,
+ .peek = qdisc_peek_head,
+ .drop = qdisc_queue_drop_head,
+ .init = fifo_init,
+ .reset = qdisc_reset_queue,
+ .change = fifo_init,
+ .dump = fifo_dump,
+ .owner = THIS_MODULE,
+};
+
/* Pass size change message down to embedded FIFO */
int fifo_set_limit(struct Qdisc *q, unsigned int limit)
{
