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net: sk_buff rbnode reorg 

skb->rbnode shares space with skb->next, skb->prev and skb->tstamp

Current uses (TCP receive ofo queue and netem) need to save/restore
tstamp, while skb->dev is either NULL (TCP) or a constant for a given
queue (netem).

Since we plan using an RB tree for TCP retransmit queue to speedup SACK
processing with large BDP, this patch exchanges skb->dev and
skb->tstamp.

This saves some overhead in both TCP and netem.

v2: removes the swtstamp field from struct tcp_skb_cb

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Wei Wang <weiwan@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
zero-colors
Eric Dumazet 2017-09-19 05:14:24 -07:00 committed by David S. Miller
parent a38b2fa37e
commit bffa72cf7f
4 changed files with 17 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
include/linux/skbuff.h
View File

@ -661,8 +661,12 @@ struct sk_buff {
struct sk_buff *prev;
union {
ktime_t tstamp;
u64 skb_mstamp;
struct net_device *dev;
/* Some protocols might use this space to store information,
* while device pointer would be NULL.
* UDP receive path is one user.
*/
unsigned long dev_scratch;
};
};
struct rb_node rbnode; /* used in netem & tcp stack */
@ -670,12 +674,8 @@ struct sk_buff {
struct sock *sk;
union {
struct net_device *dev;
/* Some protocols might use this space to store information,
* while device pointer would be NULL.
* UDP receive path is one user.
*/
unsigned long dev_scratch;
ktime_t tstamp;
u64 skb_mstamp;
};
/*
* This is the control buffer. It is free to use for every

6
include/net/tcp.h
View File

@ -797,12 +797,6 @@ struct tcp_skb_cb {
u16 tcp_gso_segs;
u16 tcp_gso_size;
};
/* Used to stash the receive timestamp while this skb is in the
* out of order queue, as skb->tstamp is overwritten by the
* rbnode.
*/
ktime_t swtstamp;
};
__u8 tcp_flags; /* TCP header flags. (tcp[13]) */

27
net/ipv4/tcp_input.c
View File

@ -4266,11 +4266,6 @@ static void tcp_sack_remove(struct tcp_sock *tp)
tp->rx_opt.num_sacks = num_sacks;
}
enum tcp_queue {
OOO_QUEUE,
RCV_QUEUE,
};
/**
* tcp_try_coalesce - try to merge skb to prior one
* @sk: socket
@ -4286,7 +4281,6 @@ enum tcp_queue {
* Returns true if caller should free @from instead of queueing it
*/
static bool tcp_try_coalesce(struct sock *sk,
enum tcp_queue dest,
struct sk_buff *to,
struct sk_buff *from,
bool *fragstolen)
@ -4311,10 +4305,7 @@ static bool tcp_try_coalesce(struct sock *sk,
if (TCP_SKB_CB(from)->has_rxtstamp) {
TCP_SKB_CB(to)->has_rxtstamp = true;
if (dest == OOO_QUEUE)
TCP_SKB_CB(to)->swtstamp = TCP_SKB_CB(from)->swtstamp;
else
to->tstamp = from->tstamp;
to->tstamp = from->tstamp;
}
return true;
@ -4351,9 +4342,6 @@ static void tcp_ofo_queue(struct sock *sk)
}
p = rb_next(p);
rb_erase(&skb->rbnode, &tp->out_of_order_queue);
/* Replace tstamp which was stomped by rbnode */
if (TCP_SKB_CB(skb)->has_rxtstamp)
skb->tstamp = TCP_SKB_CB(skb)->swtstamp;
if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
SOCK_DEBUG(sk, "ofo packet was already received\n");
@ -4365,8 +4353,7 @@ static void tcp_ofo_queue(struct sock *sk)
TCP_SKB_CB(skb)->end_seq);
tail = skb_peek_tail(&sk->sk_receive_queue);
eaten = tail && tcp_try_coalesce(sk, RCV_QUEUE,
tail, skb, &fragstolen);
eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
if (!eaten)
@ -4420,10 +4407,6 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
return;
}
/* Stash tstamp to avoid being stomped on by rbnode */
if (TCP_SKB_CB(skb)->has_rxtstamp)
TCP_SKB_CB(skb)->swtstamp = skb->tstamp;
/* Disable header prediction. */
tp->pred_flags = 0;
inet_csk_schedule_ack(sk);
@ -4451,7 +4434,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
/* In the typical case, we are adding an skb to the end of the list.
* Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
*/
if (tcp_try_coalesce(sk, OOO_QUEUE, tp->ooo_last_skb,
if (tcp_try_coalesce(sk, tp->ooo_last_skb,
skb, &fragstolen)) {
coalesce_done:
tcp_grow_window(sk, skb);
@ -4502,7 +4485,7 @@ coalesce_done:
__kfree_skb(skb1);
goto merge_right;
}
} else if (tcp_try_coalesce(sk, OOO_QUEUE, skb1,
} else if (tcp_try_coalesce(sk, skb1,
skb, &fragstolen)) {
goto coalesce_done;
}
@ -4554,7 +4537,7 @@ static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int
__skb_pull(skb, hdrlen);
eaten = (tail &&
tcp_try_coalesce(sk, RCV_QUEUE, tail,
tcp_try_coalesce(sk, tail,
skb, fragstolen)) ? 1 : 0;
tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
if (!eaten) {

7
net/sched/sch_netem.c
View File

@ -146,7 +146,6 @@ struct netem_sched_data {
*/
struct netem_skb_cb {
psched_time_t time_to_send;
ktime_t tstamp_save;
};
@ -561,7 +560,6 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
}
cb->time_to_send = now + delay;
cb->tstamp_save = skb->tstamp;
++q->counter;
tfifo_enqueue(skb, sch);
} else {
@ -629,7 +627,10 @@ deliver:
qdisc_qstats_backlog_dec(sch, skb);
skb->next = NULL;
skb->prev = NULL;
skb->tstamp = netem_skb_cb(skb)->tstamp_save;
/* skb->dev shares skb->rbnode area,
* we need to restore its value.
*/
skb->dev = qdisc_dev(sch);
#ifdef CONFIG_NET_CLS_ACT
/*