dctcp: update cwnd on congestion event

draft-ietf-tcpm-dctcp-02 says:

... when the sender receives an indication of congestion
(ECE), the sender SHOULD update cwnd as follows:

         cwnd = cwnd * (1 - DCTCP.Alpha / 2)

So, lets do this and reduce cwnd more smoothly (and faster), as per
current congestion estimate.

Cc: Lawrence Brakmo <brakmo@fb.com>
Cc: Andrew Shewmaker <agshew@gmail.com>
Cc: Glenn Judd <glenn.judd@morganstanley.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
index ab37c67756305e8548cbad657ba21a4bfc8109e0..51139175bf6143dec815be4bf71e74778aab9040 100644 (file)
--- a/net/ipv4/tcp_dctcp.c
+++ b/net/ipv4/tcp_dctcp.c
@@ -188,8 +188,8 @@ static void dctcp_ce_state_1_to_0(struct sock *sk)
 
 static void dctcp_update_alpha(struct sock *sk, u32 flags)
 {
-       const struct tcp_sock *tp = tcp_sk(sk);
        struct dctcp *ca = inet_csk_ca(sk);
+       struct tcp_sock *tp = tcp_sk(sk);
        u32 acked_bytes = tp->snd_una - ca->prior_snd_una;
 
        /* If ack did not advance snd_una, count dupack as MSS size.
@@ -229,6 +229,13 @@ static void dctcp_update_alpha(struct sock *sk, u32 flags)
                WRITE_ONCE(ca->dctcp_alpha, alpha);
                dctcp_reset(tp, ca);
        }
+
+       if (flags & CA_ACK_ECE) {
+               unsigned int cwnd = dctcp_ssthresh(sk);
+
+               if (cwnd != tp->snd_cwnd)
+                       tp->snd_cwnd = cwnd;
+       }
 }
 
 static void dctcp_state(struct sock *sk, u8 new_state)