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netem: use rb tree to implement the time queue

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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>
This commit is contained in:
Eric Dumazet 2013-06-28 07:40:57 -07:00 committed by David S. Miller
parent d0b5e51629
commit aec0a40a6f
1 changed files with 85 additions and 24 deletions
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109
net/sched/sch_netem.c
View File

@ -23,6 +23,7 @@
#include <linux/vmalloc.h> #include <linux/vmalloc.h>
#include <linux/rtnetlink.h> #include <linux/rtnetlink.h>
#include <linux/reciprocal_div.h> #include <linux/reciprocal_div.h>
#include <linux/rbtree.h>
#include <net/netlink.h> #include <net/netlink.h>
#include <net/pkt_sched.h> #include <net/pkt_sched.h>
@ -68,7 +69,8 @@
*/ */
struct netem_sched_data { 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) */ /* optional qdisc for classful handling (NULL at netem init) */
struct Qdisc *qdisc; struct Qdisc *qdisc;
@ -128,10 +130,35 @@ struct netem_sched_data {
*/ */
struct netem_skb_cb { struct netem_skb_cb {
psched_time_t time_to_send; 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) 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)); qdisc_cb_private_validate(skb, sizeof(struct netem_skb_cb));
return (struct netem_skb_cb *)qdisc_skb_cb(skb)->data; 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) 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; 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 */ while (*p) {
if (likely(!skb || tnext >= netem_skb_cb(skb)->time_to_send)) struct sk_buff *skb;
return __skb_queue_tail(list, nskb);
skb_queue_reverse_walk(list, skb) { parent = *p;
skb = netem_rb_to_skb(parent);
if (tnext >= netem_skb_cb(skb)->time_to_send) if (tnext >= netem_skb_cb(skb)->time_to_send)
break; p = &parent->rb_right;
else
p = &parent->rb_left;
} }
rb_link_node(netem_rb_node(nskb), parent, p);
__skb_queue_after(list, skb, nskb); 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(); now = psched_get_time();
if (q->rate) { 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), * Last packet in queue is reference point (now),
* calculate this time bonus and subtract * calculate this time bonus and subtract
* from delay. * 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); 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); delay += packet_len_2_sched_time(skb->len, q);
} }
cb->time_to_send = now + delay; cb->time_to_send = now + delay;
cb->tstamp_save = skb->tstamp;
++q->counter; ++q->counter;
tfifo_enqueue(skb, sch); tfifo_enqueue(skb, sch);
} else { } else {
@ -476,6 +511,21 @@ static unsigned int netem_drop(struct Qdisc *sch)
unsigned int len; unsigned int len;
len = qdisc_queue_drop(sch); 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) if (!len && q->qdisc && q->qdisc->ops->drop)
len = q->qdisc->ops->drop(q->qdisc); len = q->qdisc->ops->drop(q->qdisc);
if (len) if (len)
@ -488,19 +538,32 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
{ {
struct netem_sched_data *q = qdisc_priv(sch); struct netem_sched_data *q = qdisc_priv(sch);
struct sk_buff *skb; struct sk_buff *skb;
struct rb_node *p;
if (qdisc_is_throttled(sch)) if (qdisc_is_throttled(sch))
return NULL; return NULL;
tfifo_dequeue: tfifo_dequeue:
skb = qdisc_peek_head(sch); skb = __skb_dequeue(&sch->q);
if (skb) { 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 more time remaining? */
if (cb->time_to_send <= psched_get_time()) { if (netem_skb_cb(skb)->time_to_send <= psched_get_time()) {
__skb_unlink(skb, &sch->q); rb_erase(p, &q->t_root);
sch->qstats.backlog -= qdisc_pkt_len(skb);
sch->q.qlen--;
skb->next = NULL;
skb->prev = NULL;
skb->tstamp = netem_skb_cb(skb)->tstamp_save;
#ifdef CONFIG_NET_CLS_ACT #ifdef CONFIG_NET_CLS_ACT
/* /*
@ -522,10 +585,7 @@ tfifo_dequeue:
} }
goto tfifo_dequeue; goto tfifo_dequeue;
} }
deliver: goto deliver;
qdisc_unthrottled(sch);
qdisc_bstats_update(sch, skb);
return skb;
} }
if (q->qdisc) { if (q->qdisc) {
@ -533,7 +593,8 @@ deliver:
if (skb) if (skb)
goto deliver; 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) { if (q->qdisc) {