path: root/net/ipv4/tcp_scalable.c
diff options
authorYuchung Cheng <ycheng@google.com>2013-10-31 11:07:31 -0700
committerDavid S. Miller <davem@davemloft.net>2013-11-04 19:57:59 -0500
commit9f9843a751d0a2057f9f3d313886e7e5e6ebaac9 (patch)
treea89df5cc0c5f5280b2cfffba7f6933e4db20736f /net/ipv4/tcp_scalable.c
parenttcp: enable sockets to use MSG_FASTOPEN by default (diff)
tcp: properly handle stretch acks in slow start
Slow start now increases cwnd by 1 if an ACK acknowledges some packets, regardless the number of packets. Consequently slow start performance is highly dependent on the degree of the stretch ACKs caused by receiver or network ACK compression mechanisms (e.g., delayed-ACK, GRO, etc). But slow start algorithm is to send twice the amount of packets of packets left so it should process a stretch ACK of degree N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A follow up patch will use the remainder of the N (if greater than 1) to adjust cwnd in the congestion avoidance phase. In addition this patch retires the experimental limited slow start (LSS) feature. LSS has multiple drawbacks but questionable benefit. The fractional cwnd increase in LSS requires a loop in slow start even though it's rarely used. Configuring such an increase step via a global sysctl on different BDPS seems hard. Finally and most importantly the slow start overshoot concern is now better covered by the Hybrid slow start (hystart) enabled by default. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_scalable.c')
1 files changed, 3 insertions, 2 deletions
diff --git a/net/ipv4/tcp_scalable.c b/net/ipv4/tcp_scalable.c
index 8ce55b8aaec8..19ea6c2951f3 100644
--- a/net/ipv4/tcp_scalable.c
+++ b/net/ipv4/tcp_scalable.c
@@ -15,7 +15,8 @@
-static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
+static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 acked,
+ u32 in_flight)
struct tcp_sock *tp = tcp_sk(sk);
@@ -23,7 +24,7 @@ static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
if (tp->snd_cwnd <= tp->snd_ssthresh)
- tcp_slow_start(tp);
+ tcp_slow_start(tp, acked);
tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT));