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tcp: use TCP_SKB_CB(skb)->tcp_flags in input path

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Input path of TCP do not currently uses TCP_SKB_CB(skb)->tcp_flags,
which is only used in output path.

tcp_recvmsg(), looks at tcp_hdr(skb)->syn for every skb found in receive queue,
and its unfortunate because this bit is located in a cache line right before
the payload.

We can simplify TCP by copying tcp flags into TCP_SKB_CB(skb)->tcp_flags.

This patch does so, and avoids the cache line miss in tcp_recvmsg()

Following patches will
- allow a segment with FIN being coalesced in tcp_try_coalesce()
- simplify tcp_collapse() by not copying the headers.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2014-09-15 04:19:51 -07:00
committed by David S. Miller
parent 13bb5180e8
commit e11ecddf51
4 changed files with 17 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
net/ipv4/tcp_input.c
View File

@@ -4093,7 +4093,7 @@ static void tcp_ofo_queue(struct sock *sk)
__skb_unlink(skb, &tp->out_of_order_queue);
__skb_queue_tail(&sk->sk_receive_queue, skb);
tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
if (tcp_hdr(skb)->fin)
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
tcp_fin(sk);
}
}
@@ -4513,7 +4513,7 @@ restart:
* - bloated or contains data before "start" or
* overlaps to the next one.
*/
if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
(tcp_win_from_space(skb->truesize) > skb->len ||
before(TCP_SKB_CB(skb)->seq, start))) {
end_of_skbs = false;
@@ -4532,7 +4532,8 @@ restart:
/* Decided to skip this, advance start seq. */
start = TCP_SKB_CB(skb)->end_seq;
}
if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
if (end_of_skbs ||
(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
return;
while (before(start, end)) {
@@ -4579,8 +4580,7 @@ restart:
skb = tcp_collapse_one(sk, skb, list);
if (!skb ||
skb == tail ||
tcp_hdr(skb)->syn ||
tcp_hdr(skb)->fin)
(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
return;
}
}