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/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 2d56726..b6cdc33 100644 (file)
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -71,6 +71,7 @@ extern void qdisc_watchdog_cancel(struct qdisc_watchdog *wd);
 
 extern struct Qdisc_ops pfifo_qdisc_ops;
 extern struct Qdisc_ops bfifo_qdisc_ops;
+extern struct Qdisc_ops pfifo_head_drop_qdisc_ops;
 
 extern int fifo_set_limit(struct Qdisc *q, unsigned int limit);
 extern struct Qdisc *fifo_create_dflt(struct Qdisc *sch, struct Qdisc_ops *ops,

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index dad558b..67dc08e 100644 (file)
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -427,6 +427,25 @@ static inline struct sk_buff *qdisc_dequeue_head(struct Qdisc *sch)
        return __qdisc_dequeue_head(sch, &sch->q);
 }
 
+static inline unsigned int __qdisc_queue_drop_head(struct Qdisc *sch,
+                                             struct sk_buff_head *list)
+{
+       struct sk_buff *skb = __qdisc_dequeue_head(sch, list);
+
+       if (likely(skb != NULL)) {
+               unsigned int len = qdisc_pkt_len(skb);
+               kfree_skb(skb);
+               return len;
+       }
+
+       return 0;
+}
+
+static inline unsigned int qdisc_queue_drop_head(struct Qdisc *sch)
+{
+       return __qdisc_queue_drop_head(sch, &sch->q);
+}
+
 static inline struct sk_buff *__qdisc_dequeue_tail(struct Qdisc *sch,
                                                   struct sk_buff_head *list)
 {

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 75fd1c6..6cd4910 100644 (file)
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1707,6 +1707,7 @@ static int __init pktsched_init(void)
 {
        register_qdisc(&pfifo_qdisc_ops);
        register_qdisc(&bfifo_qdisc_ops);
+       register_qdisc(&pfifo_head_drop_qdisc_ops);
        register_qdisc(&mq_qdisc_ops);
        proc_net_fops_create(&init_net, "psched", 0, &psched_fops);
 

diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
index 69188e8..4b0a6cc 100644 (file)
--- a/net/sched/sch_fifo.c
+++ b/net/sched/sch_fifo.c
@@ -43,6 +43,26 @@ static int pfifo_enqueue(struct sk_buff *skb, struct Qdisc* sch)
        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 @@ struct Qdisc_ops bfifo_qdisc_ops __read_mostly = {
 };
 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)
 {