tcp: fill shinfo->gso_type at last moment

Our goal is to touch skb_shinfo(skb) only when absolutely needed,
to avoid two cache line misses in TCP output path for last skb
that is considered but not sent because of various conditions
(cwnd, tso defer, receiver window, TSQ...)

A packet is GSO only when skb_shinfo(skb)->gso_size is not zero.

We can set skb_shinfo(skb)->gso_type to sk->sk_gso_type even for
non GSO packets.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d4f76ab6e1368a24379a545b1277f8e697f1fc24..70a6fa8ecbd3d85ce5d7f493d5f17393ad92ab4e 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1316,16 +1316,12 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
         * code can come after this skb later on it's better to keep
         * setting gso_size to something.
         */
-       if (!skb_shinfo(prev)->gso_size) {
+       if (!skb_shinfo(prev)->gso_size)
                skb_shinfo(prev)->gso_size = mss;
-               skb_shinfo(prev)->gso_type = sk->sk_gso_type;
-       }
 
        /* CHECKME: To clear or not to clear? Mimics normal skb currently */
-       if (tcp_skb_pcount(skb) <= 1) {
+       if (tcp_skb_pcount(skb) <= 1)
                skb_shinfo(skb)->gso_size = 0;
-               skb_shinfo(skb)->gso_type = 0;
-       }
 
        /* Difference in this won't matter, both ACKed by the same cumul. ACK */
        TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index eeb59befaf06867b00e1dd6ded7742b2f0bcd821..a51f7aab27d60ed434e7393913ba3622a637b418 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -412,7 +412,6 @@ static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
 
        tcp_skb_pcount_set(skb, 1);
        shinfo->gso_size = 0;
-       shinfo->gso_type = 0;
 
        TCP_SKB_CB(skb)->seq = seq;
        if (flags & (TCPHDR_SYN | TCPHDR_FIN))
@@ -1003,6 +1002,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
        }
 
        tcp_options_write((__be32 *)(th + 1), tp, &opts);
+       skb_shinfo(skb)->gso_type = sk->sk_gso_type;
        if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
                tcp_ecn_send(sk, skb, tcp_header_size);
 
@@ -1080,11 +1080,9 @@ static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
                 */
                tcp_skb_pcount_set(skb, 1);
                shinfo->gso_size = 0;
-               shinfo->gso_type = 0;
        } else {
                tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
                shinfo->gso_size = mss_now;
-               shinfo->gso_type = sk->sk_gso_type;
        }
 }