net/ipv4/tcp_dctcp.c - arm/linux - Git at Google

 /* 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;
 	u32 loss_cwnd;
 };

 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->loss_cwnd = 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)
 {
 	struct dctcp *ca = inet_csk_ca(sk);
 	struct tcp_sock *tp = tcp_sk(sk);

 	ca->loss_cwnd = tp->snd_cwnd;
 	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)) {
 		u64 bytes_ecn = ca->acked_bytes_ecn;
 		u32 alpha = ca->dctcp_alpha;

 		/* alpha = (1 - g) * alpha + g * F */

 		alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
 		if (bytes_ecn) {
 			/* If dctcp_shift_g == 1, a 32bit value would overflow
 			 * after 8 Mbytes.
 			 */
 			bytes_ecn <<= (10 - dctcp_shift_g);
 			do_div(bytes_ecn, max(1U, ca->acked_bytes_total));

 			alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA);
 		}
 		/* dctcp_alpha can be read from dctcp_get_info() without
 		 * synchro, so we ask compiler to not use dctcp_alpha
 		 * as a temporary variable in prior operations.
 		 */
 		WRITE_ONCE(ca->dctcp_alpha, 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 size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr,
 			     union tcp_cc_info *info)
 {
 	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))) {
 		memset(&info->dctcp, 0, sizeof(info->dctcp));
 		if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
 			info->dctcp.dctcp_enabled = 1;
 			info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
 			info->dctcp.dctcp_alpha = ca->dctcp_alpha;
 			info->dctcp.dctcp_ab_ecn = ca->acked_bytes_ecn;
 			info->dctcp.dctcp_ab_tot = ca->acked_bytes_total;
 		}

 		*attr = INET_DIAG_DCTCPINFO;
 		return sizeof(info->dctcp);
 	}
 	return 0;
 }

 static u32 dctcp_cwnd_undo(struct sock *sk)
 {
 	const struct dctcp *ca = inet_csk_ca(sk);

 	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 }

 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,
 	.undo_cwnd	= dctcp_cwnd_undo,
 	.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)");
	/* 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;
	u32 loss_cwnd;
	};

	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->loss_cwnd = 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)
	{
	struct dctcp *ca = inet_csk_ca(sk);
	struct tcp_sock *tp = tcp_sk(sk);

	ca->loss_cwnd = tp->snd_cwnd;
	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)) {
	u64 bytes_ecn = ca->acked_bytes_ecn;
	u32 alpha = ca->dctcp_alpha;

	/* alpha = (1 - g) * alpha + g * F */

	alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
	if (bytes_ecn) {
	/* If dctcp_shift_g == 1, a 32bit value would overflow
	* after 8 Mbytes.
	*/
	bytes_ecn <<= (10 - dctcp_shift_g);
	do_div(bytes_ecn, max(1U, ca->acked_bytes_total));

	alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA);
	}
	/* dctcp_alpha can be read from dctcp_get_info() without
	* synchro, so we ask compiler to not use dctcp_alpha
	* as a temporary variable in prior operations.
	*/
	WRITE_ONCE(ca->dctcp_alpha, 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 size_t dctcp_get_info(struct sock sk, u32 ext, int attr,
	union tcp_cc_info *info)
	{
	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))) {
	memset(&info->dctcp, 0, sizeof(info->dctcp));
	if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
	info->dctcp.dctcp_enabled = 1;
	info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
	info->dctcp.dctcp_alpha = ca->dctcp_alpha;
	info->dctcp.dctcp_ab_ecn = ca->acked_bytes_ecn;
	info->dctcp.dctcp_ab_tot = ca->acked_bytes_total;
	}

	*attr = INET_DIAG_DCTCPINFO;
	return sizeof(info->dctcp);
	}
	return 0;
	}

	static u32 dctcp_cwnd_undo(struct sock *sk)
	{
	const struct dctcp *ca = inet_csk_ca(sk);

	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
	}

	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,
	.undo_cwnd = dctcp_cwnd_undo,
	.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)");