Commit aec0a40a authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

netem: use rb tree to implement the time queue 



Following typical setup to implement a ~100 ms RTT and big
amount of reorders has very poor performance because netem
implements the time queue using a linked list.
-----------------------------------------------------------
ETH=eth0
IFB=ifb0
modprobe ifb
ip link set dev $IFB up
tc qdisc add dev $ETH ingress 2>/dev/null
tc filter add dev $ETH parent ffff: \
   protocol ip u32 match u32 0 0 flowid 1:1 action mirred egress \
   redirect dev $IFB
ethtool -K $ETH gro off tso off gso off
tc qdisc add dev $IFB root netem delay 50ms 10ms limit 100000
tc qd add dev $ETH root netem delay 50ms limit 100000
---------------------------------------------------------

Switch netem time queue to a rb tree, so this kind of setup can work at
high speed.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d0b5e516

net/sched/sch_netem.c

+85 −24
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#include <linux/vmalloc.h>

#include <linux/rtnetlink.h>

#include <linux/reciprocal_div.h>

#include <linux/rbtree.h>



#include <net/netlink.h>

#include <net/pkt_sched.h>
@@ -68,7 +69,8 @@ 
*/



struct netem_sched_data {

	/* internal t(ime)fifo qdisc uses sch->q and sch->limit */

	/* internal t(ime)fifo qdisc uses t_root and sch->limit */

	struct rb_root t_root;



	/* optional qdisc for classful handling (NULL at netem init) */

	struct Qdisc	*qdisc;
@@ -128,10 +130,35 @@ struct netem_sched_data { 
 */

struct netem_skb_cb {

	psched_time_t	time_to_send;

	ktime_t		tstamp_save;

};



/* Because space in skb->cb[] is tight, netem overloads skb->next/prev/tstamp

 * to hold a rb_node structure.

 *

 * If struct sk_buff layout is changed, the following checks will complain.

 */

static struct rb_node *netem_rb_node(struct sk_buff *skb)

{

	BUILD_BUG_ON(offsetof(struct sk_buff, next) != 0);

	BUILD_BUG_ON(offsetof(struct sk_buff, prev) !=

		     offsetof(struct sk_buff, next) + sizeof(skb->next));

	BUILD_BUG_ON(offsetof(struct sk_buff, tstamp) !=

		     offsetof(struct sk_buff, prev) + sizeof(skb->prev));

	BUILD_BUG_ON(sizeof(struct rb_node) > sizeof(skb->next) +

					      sizeof(skb->prev) +

					      sizeof(skb->tstamp));

	return (struct rb_node *)&skb->next;

}



static struct sk_buff *netem_rb_to_skb(struct rb_node *rb)

{

	return (struct sk_buff *)rb;

}



static inline struct netem_skb_cb *netem_skb_cb(struct sk_buff *skb)

{

	/* we assume we can use skb next/prev/tstamp as storage for rb_node */

	qdisc_cb_private_validate(skb, sizeof(struct netem_skb_cb));

	return (struct netem_skb_cb *)qdisc_skb_cb(skb)->data;

}
@@ -333,20 +360,23 @@ static psched_time_t packet_len_2_sched_time(unsigned int len, struct netem_sche 


static void tfifo_enqueue(struct sk_buff *nskb, struct Qdisc *sch)

{

	struct sk_buff_head *list = &sch->q;

	struct netem_sched_data *q = qdisc_priv(sch);

	psched_time_t tnext = netem_skb_cb(nskb)->time_to_send;

	struct sk_buff *skb = skb_peek_tail(list);

	struct rb_node **p = &q->t_root.rb_node, *parent = NULL;



	/* Optimize for add at tail */

	if (likely(!skb || tnext >= netem_skb_cb(skb)->time_to_send))

		return __skb_queue_tail(list, nskb);

	while (*p) {

		struct sk_buff *skb;



	skb_queue_reverse_walk(list, skb) {

		parent = *p;

		skb = netem_rb_to_skb(parent);

		if (tnext >= netem_skb_cb(skb)->time_to_send)

			break;

			p = &parent->rb_right;

		else

			p = &parent->rb_left;

	}



	__skb_queue_after(list, skb, nskb);

	rb_link_node(netem_rb_node(nskb), parent, p);

	rb_insert_color(netem_rb_node(nskb), &q->t_root);

	sch->q.qlen++;

}



/*
@@ -436,23 +466,28 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch) 
		now = psched_get_time();



		if (q->rate) {

			struct sk_buff_head *list = &sch->q;

			struct sk_buff *last;



			if (!skb_queue_empty(list)) {

			if (!skb_queue_empty(&sch->q))

				last = skb_peek_tail(&sch->q);

			else

				last = netem_rb_to_skb(rb_last(&q->t_root));

			if (last) {

				/*

				 * Last packet in queue is reference point (now),

				 * calculate this time bonus and subtract

				 * from delay.

				 */

				delay -= netem_skb_cb(skb_peek_tail(list))->time_to_send - now;

				delay -= netem_skb_cb(last)->time_to_send - now;

				delay = max_t(psched_tdiff_t, 0, delay);

				now = netem_skb_cb(skb_peek_tail(list))->time_to_send;

				now = netem_skb_cb(last)->time_to_send;

			}



			delay += packet_len_2_sched_time(skb->len, q);

		}



		cb->time_to_send = now + delay;

		cb->tstamp_save = skb->tstamp;

		++q->counter;

		tfifo_enqueue(skb, sch);

	} else {
@@ -476,6 +511,21 @@ static unsigned int netem_drop(struct Qdisc *sch) 
	unsigned int len;



	len = qdisc_queue_drop(sch);



	if (!len) {

		struct rb_node *p = rb_first(&q->t_root);



		if (p) {

			struct sk_buff *skb = netem_rb_to_skb(p);



			rb_erase(p, &q->t_root);

			sch->q.qlen--;

			skb->next = NULL;

			skb->prev = NULL;

			len = qdisc_pkt_len(skb);

			kfree_skb(skb);

		}

	}

	if (!len && q->qdisc && q->qdisc->ops->drop)

	    len = q->qdisc->ops->drop(q->qdisc);

	if (len)
@@ -488,19 +538,32 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch) 
{

	struct netem_sched_data *q = qdisc_priv(sch);

	struct sk_buff *skb;

	struct rb_node *p;



	if (qdisc_is_throttled(sch))

		return NULL;



tfifo_dequeue:

	skb = qdisc_peek_head(sch);

	skb = __skb_dequeue(&sch->q);

	if (skb) {

		const struct netem_skb_cb *cb = netem_skb_cb(skb);

deliver:

		sch->qstats.backlog -= qdisc_pkt_len(skb);

		qdisc_unthrottled(sch);

		qdisc_bstats_update(sch, skb);

		return skb;

	}

	p = rb_first(&q->t_root);

	if (p) {

		skb = netem_rb_to_skb(p);



		/* if more time remaining? */

		if (cb->time_to_send <= psched_get_time()) {

			__skb_unlink(skb, &sch->q);

			sch->qstats.backlog -= qdisc_pkt_len(skb);

		if (netem_skb_cb(skb)->time_to_send <= psched_get_time()) {

			rb_erase(p, &q->t_root);



			sch->q.qlen--;

			skb->next = NULL;

			skb->prev = NULL;

			skb->tstamp = netem_skb_cb(skb)->tstamp_save;



#ifdef CONFIG_NET_CLS_ACT

			/*
@@ -522,10 +585,7 @@ tfifo_dequeue: 
				}

				goto tfifo_dequeue;

			}

deliver:

			qdisc_unthrottled(sch);

			qdisc_bstats_update(sch, skb);

			return skb;

			goto deliver;

		}



		if (q->qdisc) {
@@ -533,7 +593,8 @@ deliver: 
			if (skb)

				goto deliver;

		}

		qdisc_watchdog_schedule(&q->watchdog, cb->time_to_send);

		qdisc_watchdog_schedule(&q->watchdog,

					netem_skb_cb(skb)->time_to_send);

	}



	if (q->qdisc) {

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