Commit 57dbb2d8 authored by Hagen Paul Pfeifer's avatar Hagen Paul Pfeifer Committed by David S. Miller
Browse files

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: default avatarFlorian Westphal <>
Acked-by: default avatarPatrick McHardy <>
Signed-off-by: default avatarHagen Paul Pfeifer <>
Signed-off-by: default avatarDavid S. Miller <>
parent d74340d3
......@@ -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,
......@@ -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);
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)
......@@ -1707,6 +1707,7 @@ static int __init pktsched_init(void)
proc_net_fops_create(&init_net, "psched", 0, &psched_fops);
......@@ -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);
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 = {
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)
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment