Skip to content

Commit

Permalink
netem: use rb tree to implement the time queue
Browse files Browse the repository at this point in the history 
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: Eric Dumazet <edumazet@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
  • Loading branch information
Eric Dumazet authored and David S. Miller committed Jul 2, 2013
1 parent d0b5e51 commit aec0a40
Showing 1 changed file with 85 additions and 24 deletions.
109 changes: 85 additions & 24 deletions net/sched/sch_netem.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
}
Expand Down Expand Up @@ -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++;
}

/*
Expand Down Expand Up @@ -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 {
Expand All @@ -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)
Expand All @@ -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
/*
Expand All @@ -522,18 +585,16 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
}
goto tfifo_dequeue;
}
deliver:
qdisc_unthrottled(sch);
qdisc_bstats_update(sch, skb);
return skb;
goto deliver;
}

if (q->qdisc) {
skb = q->qdisc->ops->dequeue(q->qdisc);
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) {
Expand Down

0 comments on commit aec0a40

Please sign in to comment.