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diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
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+++ b/net/ipv4/tcp_dctcp.c
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+/* DataCenter TCP (DCTCP) congestion control.
+ *
+ * http://simula.stanford.edu/~alizade/Site/DCTCP.html
+ *
+ * This is an implementation of DCTCP over Reno, an enhancement to the
+ * TCP congestion control algorithm designed for data centers. DCTCP
+ * leverages Explicit Congestion Notification (ECN) in the network to
+ * provide multi-bit feedback to the end hosts. DCTCP's goal is to meet
+ * the following three data center transport requirements:
+ *
+ *  - High burst tolerance (incast due to partition/aggregate)
+ *  - Low latency (short flows, queries)
+ *  - High throughput (continuous data updates, large file transfers)
+ *    with commodity shallow buffered switches
+ *
+ * The algorithm is described in detail in the following two papers:
+ *
+ * 1) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye,
+ *    Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan:
+ *      "Data Center TCP (DCTCP)", Data Center Networks session
+ *      Proc. ACM SIGCOMM, New Delhi, 2010.
+ *   http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf
+ *
+ * 2) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar:
+ *      "Analysis of DCTCP: Stability, Convergence, and Fairness"
+ *      Proc. ACM SIGMETRICS, San Jose, 2011.
+ *   http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf
+ *
+ * Initial prototype from Abdul Kabbani, Masato Yasuda and Mohammad Alizadeh.
+ *
+ * Authors:
+ *
+ *	Daniel Borkmann <dborkman@redhat.com>
+ *	Florian Westphal <fw@strlen.de>
+ *	Glenn Judd <glenn.judd@morganstanley.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <net/tcp.h>
+#include <linux/inet_diag.h>
+
+#define DCTCP_MAX_ALPHA	1024U
+
+struct dctcp {
+	u32 acked_bytes_ecn;
+	u32 acked_bytes_total;
+	u32 prior_snd_una;
+	u32 prior_rcv_nxt;
+	u32 dctcp_alpha;
+	u32 next_seq;
+	u32 ce_state;
+	u32 delayed_ack_reserved;
+};
+
+static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */
+module_param(dctcp_shift_g, uint, 0644);
+MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha");
+
+static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA;
+module_param(dctcp_alpha_on_init, uint, 0644);
+MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value");
+
+static unsigned int dctcp_clamp_alpha_on_loss __read_mostly;
+module_param(dctcp_clamp_alpha_on_loss, uint, 0644);
+MODULE_PARM_DESC(dctcp_clamp_alpha_on_loss,
+		 "parameter for clamping alpha on loss");
+
+static struct tcp_congestion_ops dctcp_reno;
+
+static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca)
+{
+	ca->next_seq = tp->snd_nxt;
+
+	ca->acked_bytes_ecn = 0;
+	ca->acked_bytes_total = 0;
+}
+
+static void dctcp_init(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+
+	if ((tp->ecn_flags & TCP_ECN_OK) ||
+	    (sk->sk_state == TCP_LISTEN ||
+	     sk->sk_state == TCP_CLOSE)) {
+		struct dctcp *ca = inet_csk_ca(sk);
+
+		ca->prior_snd_una = tp->snd_una;
+		ca->prior_rcv_nxt = tp->rcv_nxt;
+
+		ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA);
+
+		ca->delayed_ack_reserved = 0;
+		ca->ce_state = 0;
+
+		dctcp_reset(tp, ca);
+		return;
+	}
+
+	/* No ECN support? Fall back to Reno. Also need to clear
+	 * ECT from sk since it is set during 3WHS for DCTCP.
+	 */
+	inet_csk(sk)->icsk_ca_ops = &dctcp_reno;
+	INET_ECN_dontxmit(sk);
+}
+
+static u32 dctcp_ssthresh(struct sock *sk)
+{
+	const struct dctcp *ca = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U);
+}
+
+/* Minimal DCTP CE state machine:
+ *
+ * S:	0 <- last pkt was non-CE
+ *	1 <- last pkt was CE
+ */
+
+static void dctcp_ce_state_0_to_1(struct sock *sk)
+{
+	struct dctcp *ca = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	/* State has changed from CE=0 to CE=1 and delayed
+	 * ACK has not sent yet.
+	 */
+	if (!ca->ce_state && ca->delayed_ack_reserved) {
+		u32 tmp_rcv_nxt;
+
+		/* Save current rcv_nxt. */
+		tmp_rcv_nxt = tp->rcv_nxt;
+
+		/* Generate previous ack with CE=0. */
+		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+		tp->rcv_nxt = ca->prior_rcv_nxt;
+
+		tcp_send_ack(sk);
+
+		/* Recover current rcv_nxt. */
+		tp->rcv_nxt = tmp_rcv_nxt;
+	}
+
+	ca->prior_rcv_nxt = tp->rcv_nxt;
+	ca->ce_state = 1;
+
+	tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
+}
+
+static void dctcp_ce_state_1_to_0(struct sock *sk)
+{
+	struct dctcp *ca = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	/* State has changed from CE=1 to CE=0 and delayed
+	 * ACK has not sent yet.
+	 */
+	if (ca->ce_state && ca->delayed_ack_reserved) {
+		u32 tmp_rcv_nxt;
+
+		/* Save current rcv_nxt. */
+		tmp_rcv_nxt = tp->rcv_nxt;
+
+		/* Generate previous ack with CE=1. */
+		tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
+		tp->rcv_nxt = ca->prior_rcv_nxt;
+
+		tcp_send_ack(sk);
+
+		/* Recover current rcv_nxt. */
+		tp->rcv_nxt = tmp_rcv_nxt;
+	}
+
+	ca->prior_rcv_nxt = tp->rcv_nxt;
+	ca->ce_state = 0;
+
+	tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+}
+
+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);
+	u32 acked_bytes = tp->snd_una - ca->prior_snd_una;
+
+	/* If ack did not advance snd_una, count dupack as MSS size.
+	 * If ack did update window, do not count it at all.
+	 */
+	if (acked_bytes == 0 && !(flags & CA_ACK_WIN_UPDATE))
+		acked_bytes = inet_csk(sk)->icsk_ack.rcv_mss;
+	if (acked_bytes) {
+		ca->acked_bytes_total += acked_bytes;
+		ca->prior_snd_una = tp->snd_una;
+
+		if (flags & CA_ACK_ECE)
+			ca->acked_bytes_ecn += acked_bytes;
+	}
+
+	/* Expired RTT */
+	if (!before(tp->snd_una, ca->next_seq)) {
+		/* For avoiding denominator == 1. */
+		if (ca->acked_bytes_total == 0)
+			ca->acked_bytes_total = 1;
+
+		/* alpha = (1 - g) * alpha + g * F */
+		ca->dctcp_alpha = ca->dctcp_alpha -
+				  (ca->dctcp_alpha >> dctcp_shift_g) +
+				  (ca->acked_bytes_ecn << (10U - dctcp_shift_g)) /
+				  ca->acked_bytes_total;
+
+		if (ca->dctcp_alpha > DCTCP_MAX_ALPHA)
+			/* Clamp dctcp_alpha to max. */
+			ca->dctcp_alpha = DCTCP_MAX_ALPHA;
+
+		dctcp_reset(tp, ca);
+	}
+}
+
+static void dctcp_state(struct sock *sk, u8 new_state)
+{
+	if (dctcp_clamp_alpha_on_loss && new_state == TCP_CA_Loss) {
+		struct dctcp *ca = inet_csk_ca(sk);
+
+		/* If this extension is enabled, we clamp dctcp_alpha to
+		 * max on packet loss; the motivation is that dctcp_alpha
+		 * is an indicator to the extend of congestion and packet
+		 * loss is an indicator of extreme congestion; setting
+		 * this in practice turned out to be beneficial, and
+		 * effectively assumes total congestion which reduces the
+		 * window by half.
+		 */
+		ca->dctcp_alpha = DCTCP_MAX_ALPHA;
+	}
+}
+
+static void dctcp_update_ack_reserved(struct sock *sk, enum tcp_ca_event ev)
+{
+	struct dctcp *ca = inet_csk_ca(sk);
+
+	switch (ev) {
+	case CA_EVENT_DELAYED_ACK:
+		if (!ca->delayed_ack_reserved)
+			ca->delayed_ack_reserved = 1;
+		break;
+	case CA_EVENT_NON_DELAYED_ACK:
+		if (ca->delayed_ack_reserved)
+			ca->delayed_ack_reserved = 0;
+		break;
+	default:
+		/* Don't care for the rest. */
+		break;
+	}
+}
+
+static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev)
+{
+	switch (ev) {
+	case CA_EVENT_ECN_IS_CE:
+		dctcp_ce_state_0_to_1(sk);
+		break;
+	case CA_EVENT_ECN_NO_CE:
+		dctcp_ce_state_1_to_0(sk);
+		break;
+	case CA_EVENT_DELAYED_ACK:
+	case CA_EVENT_NON_DELAYED_ACK:
+		dctcp_update_ack_reserved(sk, ev);
+		break;
+	default:
+		/* Don't care for the rest. */
+		break;
+	}
+}
+
+static void dctcp_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)
+{
+	const struct dctcp *ca = inet_csk_ca(sk);
+
+	/* Fill it also in case of VEGASINFO due to req struct limits.
+	 * We can still correctly retrieve it later.
+	 */
+	if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) ||
+	    ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
+		struct tcp_dctcp_info info;
+
+		memset(&info, 0, sizeof(info));
+		if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
+			info.dctcp_enabled = 1;
+			info.dctcp_ce_state = (u16) ca->ce_state;
+			info.dctcp_alpha = ca->dctcp_alpha;
+			info.dctcp_ab_ecn = ca->acked_bytes_ecn;
+			info.dctcp_ab_tot = ca->acked_bytes_total;
+		}
+
+		nla_put(skb, INET_DIAG_DCTCPINFO, sizeof(info), &info);
+	}
+}
+
+static struct tcp_congestion_ops dctcp __read_mostly = {
+	.init		= dctcp_init,
+	.in_ack_event   = dctcp_update_alpha,
+	.cwnd_event	= dctcp_cwnd_event,
+	.ssthresh	= dctcp_ssthresh,
+	.cong_avoid	= tcp_reno_cong_avoid,
+	.set_state	= dctcp_state,
+	.get_info	= dctcp_get_info,
+	.flags		= TCP_CONG_NEEDS_ECN,
+	.owner		= THIS_MODULE,
+	.name		= "dctcp",
+};
+
+static struct tcp_congestion_ops dctcp_reno __read_mostly = {
+	.ssthresh	= tcp_reno_ssthresh,
+	.cong_avoid	= tcp_reno_cong_avoid,
+	.get_info	= dctcp_get_info,
+	.owner		= THIS_MODULE,
+	.name		= "dctcp-reno",
+};
+
+static int __init dctcp_register(void)
+{
+	BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE);
+	return tcp_register_congestion_control(&dctcp);
+}
+
+static void __exit dctcp_unregister(void)
+{
+	tcp_unregister_congestion_control(&dctcp);
+}
+
+module_init(dctcp_register);
+module_exit(dctcp_unregister);
+
+MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
+MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
+MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>");
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("DataCenter TCP (DCTCP)");