[TCP]: Add tcp_slow_start_after_idle sysctl.

A lot of people have asked for a way to disable tcp_cwnd_restart(),
and it seems reasonable to add a sysctl to do that.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 1 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f33c9dddaa12..07bb5a2b375e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -59,6 +59,9 @@ int sysctl_tcp_tso_win_divisor = 3;
 int sysctl_tcp_mtu_probing = 0;
 int sysctl_tcp_base_mss = 512;
 
+/* By default, RFC2861 behavior.  */
+int sysctl_tcp_slow_start_after_idle = 1;
+
 static void update_send_head(struct sock *sk, struct tcp_sock *tp,
                              struct sk_buff *skb)
 {
@@ -138,7 +141,8 @@ static void tcp_event_data_sent(struct tcp_sock *tp,
         struct inet_connection_sock *icsk = inet_csk(sk);
         const u32 now = tcp_time_stamp;
 
-        if (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto)
+        if (sysctl_tcp_slow_start_after_idle &&
+            (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
                 tcp_cwnd_restart(sk, __sk_dst_get(sk));
 
         tp->lsndtime = now;