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Commit bffa72cf authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: default avatarEric 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: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a38b2fa3

include/linux/skbuff.h

+8 −8
Original line number Diff line number Diff line
@@ -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

include/net/tcp.h

+0 −6
Original line number Diff line number Diff line
@@ -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])	*/

net/ipv4/tcp_input.c

+5 −22
Original line number Diff line number Diff line
@@ -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)
@@ -4311,9 +4305,6 @@ 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;

	}
@@ -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 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) 
				__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) {

net/sched/sch_netem.c

+4 −3
Original line number Diff line number Diff line
@@ -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 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch) 
			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

			/*