[TCP] CUBIC v2.3

/*

 * TCP CUBIC: Binary Increase Congestion control for TCP v2.2

 * TCP CUBIC: Binary Increase Congestion control for TCP v2.3

 * Home page:

 *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC

 * This is from the implementation of CUBIC TCP in

 * Injong Rhee, Lisong Xu.

 *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant

 *  in PFLDnet 2005

 * Sangtae Ha, Injong Rhee and Lisong Xu,

 *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant"

 *  in ACM SIGOPS Operating System Review, July 2008.

 * Available from:

 *  http://netsrv.csc.ncsu.edu/export/cubic-paper.pdf

 *  http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf

 *

 * CUBIC integrates a new slow start algorithm, called HyStart.

 * The details of HyStart are presented in

 *  Sangtae Ha and Injong Rhee,

 *  "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.

 * Available from:

 *  http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf

 *

 * All testing results are available from:

 * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing

 *

 * Unless CUBIC is enabled and congestion window is large

 * this behaves the same as the original Reno.

					 */

#define	BICTCP_HZ		10	/* BIC HZ 2^10 = 1024 */

/* Two methods of hybrid slow start */

#define HYSTART_ACK_TRAIN	0x1

#define HYSTART_DELAY		0x2

/* Number of delay samples for detecting the increase of delay */

#define HYSTART_MIN_SAMPLES	8

#define HYSTART_DELAY_MIN	(2U<<3)

#define HYSTART_DELAY_MAX	(16U<<3)

#define HYSTART_DELAY_THRESH(x)	clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)

static int fast_convergence __read_mostly = 1;

static int beta __read_mostly = 717;	/* = 717/1024 (BICTCP_BETA_SCALE) */

static int initial_ssthresh __read_mostly;

static int bic_scale __read_mostly = 41;

static int tcp_friendliness __read_mostly = 1;

static int hystart __read_mostly = 1;

static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;

static int hystart_low_window __read_mostly = 16;

static u32 cube_rtt_scale __read_mostly;

static u32 beta_scale __read_mostly;

static u64 cube_factor __read_mostly;

MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");

module_param(tcp_friendliness, int, 0644);

MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");

module_param(hystart, int, 0644);

MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");

module_param(hystart_detect, int, 0644);

MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms"

		 " 1: packet-train 2: delay 3: both packet-train and delay");

module_param(hystart_low_window, int, 0644);

MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");

/* BIC TCP Parameters */

struct bictcp {

	u32	ack_cnt;	/* number of acks */

	u32	tcp_cwnd;	/* estimated tcp cwnd */

#define ACK_RATIO_SHIFT	4

	u32	delayed_ack;	/* estimate the ratio of Packets/ACKs << 4 */

	u16	delayed_ack;	/* estimate the ratio of Packets/ACKs << 4 */

	u8	sample_cnt;	/* number of samples to decide curr_rtt */

	u8	found;		/* the exit point is found? */

	u32	round_start;	/* beginning of each round */

	u32	end_seq;	/* end_seq of the round */

	u32	last_jiffies;	/* last time when the ACK spacing is close */

	u32	curr_rtt;	/* the minimum rtt of current round */

};

static inline void bictcp_reset(struct bictcp *ca)

	ca->delayed_ack = 2 << ACK_RATIO_SHIFT;

	ca->ack_cnt = 0;

	ca->tcp_cwnd = 0;

	ca->found = 0;

}

static inline void bictcp_hystart_reset(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct bictcp *ca = inet_csk_ca(sk);

	ca->round_start = ca->last_jiffies = jiffies;

	ca->end_seq = tp->snd_nxt;

	ca->curr_rtt = 0;

	ca->sample_cnt = 0;

}

static void bictcp_init(struct sock *sk)

{

	bictcp_reset(inet_csk_ca(sk));

	if (initial_ssthresh)

	if (hystart)

		bictcp_hystart_reset(sk);

	if (!hystart && initial_ssthresh)

		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;

}

	if (!tcp_is_cwnd_limited(sk, in_flight))

		return;

	if (tp->snd_cwnd <= tp->snd_ssthresh)

	if (tp->snd_cwnd <= tp->snd_ssthresh) {

		if (hystart && after(ack, ca->end_seq))

			bictcp_hystart_reset(sk);

		tcp_slow_start(tp);

	else {

	} else {

		bictcp_update(ca, tp->snd_cwnd);

		/* In dangerous area, increase slowly.

static void bictcp_state(struct sock *sk, u8 new_state)

{

	if (new_state == TCP_CA_Loss)

	if (new_state == TCP_CA_Loss) {

		bictcp_reset(inet_csk_ca(sk));

		bictcp_hystart_reset(sk);

	}

}

static void hystart_update(struct sock *sk, u32 delay)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct bictcp *ca = inet_csk_ca(sk);

	if (!(ca->found & hystart_detect)) {

		u32 curr_jiffies = jiffies;

		/* first detection parameter - ack-train detection */

		if (curr_jiffies - ca->last_jiffies <= msecs_to_jiffies(2)) {

			ca->last_jiffies = curr_jiffies;

			if (curr_jiffies - ca->round_start >= ca->delay_min>>4)

				ca->found |= HYSTART_ACK_TRAIN;

		}

		/* obtain the minimum delay of more than sampling packets */

		if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {

			if (ca->curr_rtt == 0 || ca->curr_rtt > delay)

				ca->curr_rtt = delay;

			ca->sample_cnt++;

		} else {

			if (ca->curr_rtt > ca->delay_min +

			    HYSTART_DELAY_THRESH(ca->delay_min>>4))

				ca->found |= HYSTART_DELAY;

		}

		/*

		 * Either one of two conditions are met,

		 * we exit from slow start immediately.

		 */

		if (ca->found & hystart_detect)

			tp->snd_ssthresh = tp->snd_cwnd;

	}

}

/* Track delayed acknowledgment ratio using sliding window

static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)

{

	const struct inet_connection_sock *icsk = inet_csk(sk);

	const struct tcp_sock *tp = tcp_sk(sk);

	struct bictcp *ca = inet_csk_ca(sk);

	u32 delay;

	/* first time call or link delay decreases */

	if (ca->delay_min == 0 || ca->delay_min > delay)

		ca->delay_min = delay;

	/* hystart triggers when cwnd is larger than some threshold */

	if (hystart && tp->snd_cwnd <= tp->snd_ssthresh &&

	    tp->snd_cwnd >= hystart_low_window)

		hystart_update(sk, delay);

}

static struct tcp_congestion_ops cubictcp = {

MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");

MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("CUBIC TCP");

MODULE_VERSION("2.2");

MODULE_VERSION("2.3");