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>

4 files changed, 17 insertions, 39 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 72299ef00061..492828801acb 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -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
diff --git a/include/net/tcp.h b/include/net/tcp.h
index b510f284427a..49a8a46466f3 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -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])  */
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bddf724f5c02..db9bb46b5776 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -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) {
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index b1266e75ca43..063a4bdb9ee6 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -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
                         /*