tcp: defer sacked assignment

While chasing tcp_xmit_retransmit_queue() kasan issue, I found
that we could avoid reading sacked field of skb that we wont send,
possibly removing one cache line miss.

Very minor change in slow path, but why not ? ;)

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

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index bdaef7fd6e47701b2d2280e1f40f816e1920c432..8b45794eb6b2600c914e504b8031f61dbbe164a3 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2776,7 +2776,7 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 
        max_segs = tcp_tso_autosize(sk, tcp_current_mss(sk));
        tcp_for_write_queue_from(skb, sk) {
-               __u8 sacked = TCP_SKB_CB(skb)->sacked;
+               __u8 sacked;
                int segs;
 
                if (skb == tcp_send_head(sk))
@@ -2788,6 +2788,7 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
                segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
                if (segs <= 0)
                        return;
+               sacked = TCP_SKB_CB(skb)->sacked;
                /* In case tcp_shift_skb_data() have aggregated large skbs,
                 * we need to make sure not sending too bigs TSO packets
                 */