Commit 47805667 authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

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: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0fa1dfd6

net/ipv4/tcp_dctcp.c

+8 −1
Original line number Diff line number Diff line
@@ -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)

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