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

 /*
  * TCP Westwood+: end-to-end bandwidth estimation for TCP
  *
  *      Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4
  *
  * Support at http://c3lab.poliba.it/index.php/Westwood
  * Main references in literature:
  *
  * - Mascolo S, Casetti, M. Gerla et al.
  *   "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001
  *
  * - A. Grieco, s. Mascolo
  *   "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer
  *     Comm. Review, 2004
  *
  * - A. Dell'Aera, L. Grieco, S. Mascolo.
  *   "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving :
  *    A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004
  *
  * Westwood+ employs end-to-end bandwidth measurement to set cwnd and
  * ssthresh after packet loss. The probing phase is as the original Reno.
  */

 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/skbuff.h>
 #include <linux/inet_diag.h>
 #include <net/tcp.h>

 /* TCP Westwood structure */
 struct westwood {
 	u32    bw_ns_est;        /* first bandwidth estimation..not too smoothed 8) */
 	u32    bw_est;           /* bandwidth estimate */
 	u32    rtt_win_sx;       /* here starts a new evaluation... */
 	u32    bk;
 	u32    snd_una;          /* used for evaluating the number of acked bytes */
 	u32    cumul_ack;
 	u32    accounted;
 	u32    rtt;
 	u32    rtt_min;          /* minimum observed RTT */
 	u8     first_ack;        /* flag which infers that this is the first ack */
 	u8     reset_rtt_min;    /* Reset RTT min to next RTT sample*/
 };

 /* TCP Westwood functions and constants */
 #define TCP_WESTWOOD_RTT_MIN   (HZ/20)	/* 50ms */
 #define TCP_WESTWOOD_INIT_RTT  (20*HZ)	/* maybe too conservative?! */

 /*
  * @tcp_westwood_create
  * This function initializes fields used in TCP Westwood+,
  * it is called after the initial SYN, so the sequence numbers
  * are correct but new passive connections we have no
  * information about RTTmin at this time so we simply set it to
  * TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative
  * since in this way we're sure it will be updated in a consistent
  * way as soon as possible. It will reasonably happen within the first
  * RTT period of the connection lifetime.
  */
 static void tcp_westwood_init(struct sock *sk)
 {
 	struct westwood *w = inet_csk_ca(sk);

 	w->bk = 0;
 	w->bw_ns_est = 0;
 	w->bw_est = 0;
 	w->accounted = 0;
 	w->cumul_ack = 0;
 	w->reset_rtt_min = 1;
 	w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
 	w->rtt_win_sx = tcp_jiffies32;
 	w->snd_una = tcp_sk(sk)->snd_una;
 	w->first_ack = 1;
 }

 /*
  * @westwood_do_filter
  * Low-pass filter. Implemented using constant coefficients.
  */
 static inline u32 westwood_do_filter(u32 a, u32 b)
 {
 	return ((7 * a) + b) >> 3;
 }

 static void westwood_filter(struct westwood *w, u32 delta)
 {
 	/* If the filter is empty fill it with the first sample of bandwidth  */
 	if (w->bw_ns_est == 0 && w->bw_est == 0) {
 		w->bw_ns_est = w->bk / delta;
 		w->bw_est = w->bw_ns_est;
 	} else {
 		w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
 		w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
 	}
 }

 /*
  * @westwood_pkts_acked
  * Called after processing group of packets.
  * but all westwood needs is the last sample of srtt.
  */
 static void tcp_westwood_pkts_acked(struct sock *sk,
 				    const struct ack_sample *sample)
 {
 	struct westwood *w = inet_csk_ca(sk);

 	if (sample->rtt_us > 0)
 		w->rtt = usecs_to_jiffies(sample->rtt_us);
 }

 /*
  * @westwood_update_window
  * It updates RTT evaluation window if it is the right moment to do
  * it. If so it calls filter for evaluating bandwidth.
  */
 static void westwood_update_window(struct sock *sk)
 {
 	struct westwood *w = inet_csk_ca(sk);
 	s32 delta = tcp_jiffies32 - w->rtt_win_sx;

 	/* Initialize w->snd_una with the first acked sequence number in order
 	 * to fix mismatch between tp->snd_una and w->snd_una for the first
 	 * bandwidth sample
 	 */
 	if (w->first_ack) {
 		w->snd_una = tcp_sk(sk)->snd_una;
 		w->first_ack = 0;
 	}

 	/*
 	 * See if a RTT-window has passed.
 	 * Be careful since if RTT is less than
 	 * 50ms we don't filter but we continue 'building the sample'.
 	 * This minimum limit was chosen since an estimation on small
 	 * time intervals is better to avoid...
 	 * Obviously on a LAN we reasonably will always have
 	 * right_bound = left_bound + WESTWOOD_RTT_MIN
 	 */
 	if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {
 		westwood_filter(w, delta);

 		w->bk = 0;
 		w->rtt_win_sx = tcp_jiffies32;
 	}
 }

 static inline void update_rtt_min(struct westwood *w)
 {
 	if (w->reset_rtt_min) {
 		w->rtt_min = w->rtt;
 		w->reset_rtt_min = 0;
 	} else
 		w->rtt_min = min(w->rtt, w->rtt_min);
 }

 /*
  * @westwood_fast_bw
  * It is called when we are in fast path. In particular it is called when
  * header prediction is successful. In such case in fact update is
  * straight forward and doesn't need any particular care.
  */
 static inline void westwood_fast_bw(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct westwood *w = inet_csk_ca(sk);

 	westwood_update_window(sk);

 	w->bk += tp->snd_una - w->snd_una;
 	w->snd_una = tp->snd_una;
 	update_rtt_min(w);
 }

 /*
  * @westwood_acked_count
  * This function evaluates cumul_ack for evaluating bk in case of
  * delayed or partial acks.
  */
 static inline u32 westwood_acked_count(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct westwood *w = inet_csk_ca(sk);

 	w->cumul_ack = tp->snd_una - w->snd_una;

 	/* If cumul_ack is 0 this is a dupack since it's not moving
 	 * tp->snd_una.
 	 */
 	if (!w->cumul_ack) {
 		w->accounted += tp->mss_cache;
 		w->cumul_ack = tp->mss_cache;
 	}

 	if (w->cumul_ack > tp->mss_cache) {
 		/* Partial or delayed ack */
 		if (w->accounted >= w->cumul_ack) {
 			w->accounted -= w->cumul_ack;
 			w->cumul_ack = tp->mss_cache;
 		} else {
 			w->cumul_ack -= w->accounted;
 			w->accounted = 0;
 		}
 	}

 	w->snd_una = tp->snd_una;

 	return w->cumul_ack;
 }

 /*
  * TCP Westwood
  * Here limit is evaluated as Bw estimation*RTTmin (for obtaining it
  * in packets we use mss_cache). Rttmin is guaranteed to be >= 2
  * so avoids ever returning 0.
  */
 static u32 tcp_westwood_bw_rttmin(const struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct westwood *w = inet_csk_ca(sk);

 	return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
 }

 static void tcp_westwood_ack(struct sock *sk, u32 ack_flags)
 {
 	if (ack_flags & CA_ACK_SLOWPATH) {
 		struct westwood *w = inet_csk_ca(sk);

 		westwood_update_window(sk);
 		w->bk += westwood_acked_count(sk);

 		update_rtt_min(w);
 		return;
 	}

 	westwood_fast_bw(sk);
 }

 static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct westwood *w = inet_csk_ca(sk);

 	switch (event) {
 	case CA_EVENT_COMPLETE_CWR:
 		tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
 		break;
 	case CA_EVENT_LOSS:
 		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
 		/* Update RTT_min when next ack arrives */
 		w->reset_rtt_min = 1;
 		break;
 	default:
 		/* don't care */
 		break;
 	}
 }

 /* Extract info for Tcp socket info provided via netlink. */
 static size_t tcp_westwood_info(struct sock *sk, u32 ext, int *attr,
 				union tcp_cc_info *info)
 {
 	const struct westwood *ca = inet_csk_ca(sk);

 	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
 		info->vegas.tcpv_enabled = 1;
 		info->vegas.tcpv_rttcnt	= 0;
 		info->vegas.tcpv_rtt	= jiffies_to_usecs(ca->rtt);
 		info->vegas.tcpv_minrtt	= jiffies_to_usecs(ca->rtt_min);

 		*attr = INET_DIAG_VEGASINFO;
 		return sizeof(struct tcpvegas_info);
 	}
 	return 0;
 }

 static struct tcp_congestion_ops tcp_westwood __read_mostly = {
 	.init		= tcp_westwood_init,
 	.ssthresh	= tcp_reno_ssthresh,
 	.cong_avoid	= tcp_reno_cong_avoid,
 	.undo_cwnd      = tcp_reno_undo_cwnd,
 	.cwnd_event	= tcp_westwood_event,
 	.in_ack_event	= tcp_westwood_ack,
 	.get_info	= tcp_westwood_info,
 	.pkts_acked	= tcp_westwood_pkts_acked,

 	.owner		= THIS_MODULE,
 	.name		= "westwood"
 };

 static int __init tcp_westwood_register(void)
 {
 	BUILD_BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE);
 	return tcp_register_congestion_control(&tcp_westwood);
 }

 static void __exit tcp_westwood_unregister(void)
 {
 	tcp_unregister_congestion_control(&tcp_westwood);
 }

 module_init(tcp_westwood_register);
 module_exit(tcp_westwood_unregister);

 MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("TCP Westwood+");
	/*
	* TCP Westwood+: end-to-end bandwidth estimation for TCP
	*
	* Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4
	*
	* Support at http://c3lab.poliba.it/index.php/Westwood
	* Main references in literature:
	*
	* - Mascolo S, Casetti, M. Gerla et al.
	* "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001
	*
	* - A. Grieco, s. Mascolo
	* "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer
	* Comm. Review, 2004
	*
	* - A. Dell'Aera, L. Grieco, S. Mascolo.
	* "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving :
	* A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004
	*
	* Westwood+ employs end-to-end bandwidth measurement to set cwnd and
	* ssthresh after packet loss. The probing phase is as the original Reno.
	*/

	#include <linux/mm.h>
	#include <linux/module.h>
	#include <linux/skbuff.h>
	#include <linux/inet_diag.h>
	#include <net/tcp.h>

	/* TCP Westwood structure */
	struct westwood {
	u32 bw_ns_est; /* first bandwidth estimation..not too smoothed 8) */
	u32 bw_est; /* bandwidth estimate */
	u32 rtt_win_sx; /* here starts a new evaluation... */
	u32 bk;
	u32 snd_una; /* used for evaluating the number of acked bytes */
	u32 cumul_ack;
	u32 accounted;
	u32 rtt;
	u32 rtt_min; /* minimum observed RTT */
	u8 first_ack; /* flag which infers that this is the first ack */
	u8 reset_rtt_min; /* Reset RTT min to next RTT sample*/
	};

	/* TCP Westwood functions and constants */
	#define TCP_WESTWOOD_RTT_MIN (HZ/20) /* 50ms */
	#define TCP_WESTWOOD_INIT_RTT (20HZ) / maybe too conservative?! */

	/*
	* @tcp_westwood_create
	* This function initializes fields used in TCP Westwood+,
	* it is called after the initial SYN, so the sequence numbers
	* are correct but new passive connections we have no
	* information about RTTmin at this time so we simply set it to
	* TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative
	* since in this way we're sure it will be updated in a consistent
	* way as soon as possible. It will reasonably happen within the first
	* RTT period of the connection lifetime.
	*/
	static void tcp_westwood_init(struct sock *sk)
	{
	struct westwood *w = inet_csk_ca(sk);

	w->bk = 0;
	w->bw_ns_est = 0;
	w->bw_est = 0;
	w->accounted = 0;
	w->cumul_ack = 0;
	w->reset_rtt_min = 1;
	w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
	w->rtt_win_sx = tcp_jiffies32;
	w->snd_una = tcp_sk(sk)->snd_una;
	w->first_ack = 1;
	}

	/*
	* @westwood_do_filter
	* Low-pass filter. Implemented using constant coefficients.
	*/
	static inline u32 westwood_do_filter(u32 a, u32 b)
	{
	return ((7 * a) + b) >> 3;
	}

	static void westwood_filter(struct westwood *w, u32 delta)
	{
	/* If the filter is empty fill it with the first sample of bandwidth */
	if (w->bw_ns_est == 0 && w->bw_est == 0) {
	w->bw_ns_est = w->bk / delta;
	w->bw_est = w->bw_ns_est;
	} else {
	w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
	w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
	}
	}

	/*
	* @westwood_pkts_acked
	* Called after processing group of packets.
	* but all westwood needs is the last sample of srtt.
	*/
	static void tcp_westwood_pkts_acked(struct sock *sk,
	const struct ack_sample *sample)
	{
	struct westwood *w = inet_csk_ca(sk);

	if (sample->rtt_us > 0)
	w->rtt = usecs_to_jiffies(sample->rtt_us);
	}

	/*
	* @westwood_update_window
	* It updates RTT evaluation window if it is the right moment to do
	* it. If so it calls filter for evaluating bandwidth.
	*/
	static void westwood_update_window(struct sock *sk)
	{
	struct westwood *w = inet_csk_ca(sk);
	s32 delta = tcp_jiffies32 - w->rtt_win_sx;

	/* Initialize w->snd_una with the first acked sequence number in order
	* to fix mismatch between tp->snd_una and w->snd_una for the first
	* bandwidth sample
	*/
	if (w->first_ack) {
	w->snd_una = tcp_sk(sk)->snd_una;
	w->first_ack = 0;
	}

	/*
	* See if a RTT-window has passed.
	* Be careful since if RTT is less than
	* 50ms we don't filter but we continue 'building the sample'.
	* This minimum limit was chosen since an estimation on small
	* time intervals is better to avoid...
	* Obviously on a LAN we reasonably will always have
	* right_bound = left_bound + WESTWOOD_RTT_MIN
	*/
	if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {
	westwood_filter(w, delta);

	w->bk = 0;
	w->rtt_win_sx = tcp_jiffies32;
	}
	}

	static inline void update_rtt_min(struct westwood *w)
	{
	if (w->reset_rtt_min) {
	w->rtt_min = w->rtt;
	w->reset_rtt_min = 0;
	} else
	w->rtt_min = min(w->rtt, w->rtt_min);
	}

	/*
	* @westwood_fast_bw
	* It is called when we are in fast path. In particular it is called when
	* header prediction is successful. In such case in fact update is
	* straight forward and doesn't need any particular care.
	*/
	static inline void westwood_fast_bw(struct sock *sk)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct westwood *w = inet_csk_ca(sk);

	westwood_update_window(sk);

	w->bk += tp->snd_una - w->snd_una;
	w->snd_una = tp->snd_una;
	update_rtt_min(w);
	}

	/*
	* @westwood_acked_count
	* This function evaluates cumul_ack for evaluating bk in case of
	* delayed or partial acks.
	*/
	static inline u32 westwood_acked_count(struct sock *sk)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct westwood *w = inet_csk_ca(sk);

	w->cumul_ack = tp->snd_una - w->snd_una;

	/* If cumul_ack is 0 this is a dupack since it's not moving
	* tp->snd_una.
	*/
	if (!w->cumul_ack) {
	w->accounted += tp->mss_cache;
	w->cumul_ack = tp->mss_cache;
	}

	if (w->cumul_ack > tp->mss_cache) {
	/* Partial or delayed ack */
	if (w->accounted >= w->cumul_ack) {
	w->accounted -= w->cumul_ack;
	w->cumul_ack = tp->mss_cache;
	} else {
	w->cumul_ack -= w->accounted;
	w->accounted = 0;
	}
	}

	w->snd_una = tp->snd_una;

	return w->cumul_ack;
	}

	/*
	* TCP Westwood
	* Here limit is evaluated as Bw estimation*RTTmin (for obtaining it
	* in packets we use mss_cache). Rttmin is guaranteed to be >= 2
	* so avoids ever returning 0.
	*/
	static u32 tcp_westwood_bw_rttmin(const struct sock *sk)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	const struct westwood *w = inet_csk_ca(sk);

	return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
	}

	static void tcp_westwood_ack(struct sock *sk, u32 ack_flags)
	{
	if (ack_flags & CA_ACK_SLOWPATH) {
	struct westwood *w = inet_csk_ca(sk);

	westwood_update_window(sk);
	w->bk += westwood_acked_count(sk);

	update_rtt_min(w);
	return;
	}

	westwood_fast_bw(sk);
	}

	static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
	{
	struct tcp_sock *tp = tcp_sk(sk);
	struct westwood *w = inet_csk_ca(sk);

	switch (event) {
	case CA_EVENT_COMPLETE_CWR:
	tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
	break;
	case CA_EVENT_LOSS:
	tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
	/* Update RTT_min when next ack arrives */
	w->reset_rtt_min = 1;
	break;
	default:
	/* don't care */
	break;
	}
	}

	/* Extract info for Tcp socket info provided via netlink. */
	static size_t tcp_westwood_info(struct sock sk, u32 ext, int attr,
	union tcp_cc_info *info)
	{
	const struct westwood *ca = inet_csk_ca(sk);

	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
	info->vegas.tcpv_enabled = 1;
	info->vegas.tcpv_rttcnt = 0;
	info->vegas.tcpv_rtt = jiffies_to_usecs(ca->rtt);
	info->vegas.tcpv_minrtt = jiffies_to_usecs(ca->rtt_min);

	*attr = INET_DIAG_VEGASINFO;
	return sizeof(struct tcpvegas_info);
	}
	return 0;
	}

	static struct tcp_congestion_ops tcp_westwood __read_mostly = {
	.init = tcp_westwood_init,
	.ssthresh = tcp_reno_ssthresh,
	.cong_avoid = tcp_reno_cong_avoid,
	.undo_cwnd = tcp_reno_undo_cwnd,
	.cwnd_event = tcp_westwood_event,
	.in_ack_event = tcp_westwood_ack,
	.get_info = tcp_westwood_info,
	.pkts_acked = tcp_westwood_pkts_acked,

	.owner = THIS_MODULE,
	.name = "westwood"
	};

	static int __init tcp_westwood_register(void)
	{
	BUILD_BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE);
	return tcp_register_congestion_control(&tcp_westwood);
	}

	static void __exit tcp_westwood_unregister(void)
	{
	tcp_unregister_congestion_control(&tcp_westwood);
	}

	module_init(tcp_westwood_register);
	module_exit(tcp_westwood_unregister);

	MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera");
	MODULE_LICENSE("GPL");
	MODULE_DESCRIPTION("TCP Westwood+");