From 2331ccc5b3231c35b758fe274f45fbed38467f94 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 1 Nov 2016 10:53:42 -0700 Subject: [PATCH] tcp: enhance tcp collapsing MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit As Ilya Lesokhin suggested, we can collapse two skbs at retransmit time even if the skb at the right has fragments. We simply have to use more generic skb_copy_bits() instead of skb_copy_from_linear_data() in tcp_collapse_retrans() Also need to guard this skb_copy_bits() in case there is nothing to copy, otherwise skb_put() could panic if left skb has frags. Tested: Used following packetdrill test // Establish a connection. 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0 +0 < S 0:0(0) win 32792 +0 > S. 0:0(0) ack 1 +.100 < . 1:1(0) ack 1 win 257 +0 accept(3, ..., ...) = 4 +0 setsockopt(4, SOL_TCP, TCP_NODELAY, [1], 4) = 0 +0 write(4, ..., 200) = 200 +0 > P. 1:201(200) ack 1 +.001 write(4, ..., 200) = 200 +0 > P. 201:401(200) ack 1 +.001 write(4, ..., 200) = 200 +0 > P. 401:601(200) ack 1 +.001 write(4, ..., 200) = 200 +0 > P. 601:801(200) ack 1 +.001 write(4, ..., 200) = 200 +0 > P. 801:1001(200) ack 1 +.001 write(4, ..., 100) = 100 +0 > P. 1001:1101(100) ack 1 +.001 write(4, ..., 100) = 100 +0 > P. 1101:1201(100) ack 1 +.001 write(4, ..., 100) = 100 +0 > P. 1201:1301(100) ack 1 +.001 write(4, ..., 100) = 100 +0 > P. 1301:1401(100) ack 1 +.100 < . 1:1(0) ack 1 win 257 // Check that TCP collapse works : +0 > P. 1:1001(1000) ack 1 Reported-by: Ilya Lesokhin Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Yuchung Cheng Cc: Ilpo Järvinen Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 896e9dfbdb5c..f57b5aa51b59 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2529,8 +2529,9 @@ static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb) tcp_unlink_write_queue(next_skb, sk); - skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size), - next_skb_size); + if (next_skb_size) + skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size), + next_skb_size); if (next_skb->ip_summed == CHECKSUM_PARTIAL) skb->ip_summed = CHECKSUM_PARTIAL; @@ -2567,14 +2568,11 @@ static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb) { if (tcp_skb_pcount(skb) > 1) return false; - /* TODO: SACK collapsing could be used to remove this condition */ - if (skb_shinfo(skb)->nr_frags != 0) - return false; if (skb_cloned(skb)) return false; if (skb == tcp_send_head(sk)) return false; - /* Some heurestics for collapsing over SACK'd could be invented */ + /* Some heuristics for collapsing over SACK'd could be invented */ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) return false; -- 2.20.1