tcp: defer sacked assignment (dca0aaf8) · Commits · 戴 / test

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>

net/ipv4/tcp_output.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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
		*/

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