From 10d3be569243def8d92ac3722395ef5a59c504e6 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 21 Apr 2016 10:55:23 -0700 Subject: tcp-tso: do not split TSO packets at retransmit time Linux TCP stack painfully segments all TSO/GSO packets before retransmits. This was fine back in the days when TSO/GSO were emerging, with their bugs, but we believe the dark age is over. Keeping big packets in write queues, but also in stack traversal has a lot of benefits. - Less memory overhead, because write queues have less skbs - Less cpu overhead at ACK processing. - Better SACK processing, as lot of studies mentioned how awful linux was at this ;) - Less cpu overhead to send the rtx packets (IP stack traversal, netfilter traversal, drivers...) - Better latencies in presence of losses. - Smaller spikes in fq like packet schedulers, as retransmits are not constrained by TCP Small Queues. 1 % packet losses are common today, and at 100Gbit speeds, this translates to ~80,000 losses per second. Losses are often correlated, and we see many retransmit events leading to 1-MSS train of packets, at the time hosts are already under stress. Signed-off-by: Eric Dumazet Acked-by: Yuchung Cheng Signed-off-by: David S. Miller --- net/ipv4/tcp_timer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'net/ipv4/tcp_timer.c') diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 49bc474f8e35..373b03e78aaa 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -404,7 +404,7 @@ void tcp_retransmit_timer(struct sock *sk) goto out; } tcp_enter_loss(sk); - tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); + tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1); __sk_dst_reset(sk); goto out_reset_timer; } @@ -436,7 +436,7 @@ void tcp_retransmit_timer(struct sock *sk) tcp_enter_loss(sk); - if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { + if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1) > 0) { /* Retransmission failed because of local congestion, * do not backoff. */ -- cgit v1.2.3-59-g8ed1b