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 <edumazet@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 49bc474..373b03e 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -404,7 +404,7 @@
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 @@
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.
*/