Subversion Repositories or1k_soc_on_altera_embedded_dev_kit

/*

 * H-TCP congestion control. The algorithm is detailed in:

 * R.N.Shorten, D.J.Leith:

 *   "H-TCP: TCP for high-speed and long-distance networks"

 *   Proc. PFLDnet, Argonne, 2004.

 * http://www.hamilton.ie/net/htcp3.pdf

 */

#include <linux/mm.h>

#include <linux/module.h>

#include <net/tcp.h>

#define ALPHA_BASE      (1<<7)  /* 1.0 with shift << 7 */

#define BETA_MIN        (1<<6)  /* 0.5 with shift << 7 */

#define BETA_MAX        102     /* 0.8 with shift << 7 */

static int use_rtt_scaling __read_mostly = 1;

module_param(use_rtt_scaling, int, 0644);

MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");

static int use_bandwidth_switch __read_mostly = 1;

module_param(use_bandwidth_switch, int, 0644);

MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");

struct htcp {

        u32     alpha;          /* Fixed point arith, << 7 */

        u8      beta;           /* Fixed point arith, << 7 */

        u8      modeswitch;     /* Delay modeswitch

                                   until we had at least one congestion event */

        u16     pkts_acked;

        u32     packetcount;

        u32     minRTT;

        u32     maxRTT;

        u32     last_cong;      /* Time since last congestion event end */

        u32     undo_last_cong;

        u32     undo_maxRTT;

        u32     undo_old_maxB;

        /* Bandwidth estimation */

        u32     minB;

        u32     maxB;

        u32     old_maxB;

        u32     Bi;

        u32     lasttime;

};

static inline u32 htcp_cong_time(const struct htcp *ca)

{

        return jiffies - ca->last_cong;

}

static inline u32 htcp_ccount(const struct htcp *ca)

{

        return htcp_cong_time(ca) / ca->minRTT;

}

static inline void htcp_reset(struct htcp *ca)

{

        ca->undo_last_cong = ca->last_cong;

        ca->undo_maxRTT = ca->maxRTT;

        ca->undo_old_maxB = ca->old_maxB;

        ca->last_cong = jiffies;

}

static u32 htcp_cwnd_undo(struct sock *sk)

{

        const struct tcp_sock *tp = tcp_sk(sk);

        struct htcp *ca = inet_csk_ca(sk);

        ca->last_cong = ca->undo_last_cong;

        ca->maxRTT = ca->undo_maxRTT;

        ca->old_maxB = ca->undo_old_maxB;

        return max(tp->snd_cwnd, (tp->snd_ssthresh << 7) / ca->beta);

}

static inline void measure_rtt(struct sock *sk, u32 srtt)

{

        const struct inet_connection_sock *icsk = inet_csk(sk);

        struct htcp *ca = inet_csk_ca(sk);

        /* keep track of minimum RTT seen so far, minRTT is zero at first */

        if (ca->minRTT > srtt || !ca->minRTT)

                ca->minRTT = srtt;

        /* max RTT */

        if (icsk->icsk_ca_state == TCP_CA_Open) {

                if (ca->maxRTT < ca->minRTT)

                        ca->maxRTT = ca->minRTT;

                if (ca->maxRTT < srtt

                    && srtt <= ca->maxRTT + msecs_to_jiffies(20))

                        ca->maxRTT = srtt;

        }

}

static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked, s32 rtt)

{

        const struct inet_connection_sock *icsk = inet_csk(sk);

        const struct tcp_sock *tp = tcp_sk(sk);

        struct htcp *ca = inet_csk_ca(sk);

        u32 now = tcp_time_stamp;

        if (icsk->icsk_ca_state == TCP_CA_Open)

                ca->pkts_acked = pkts_acked;

        if (rtt > 0)

                measure_rtt(sk, usecs_to_jiffies(rtt));

        if (!use_bandwidth_switch)

                return;

        /* achieved throughput calculations */

        if (icsk->icsk_ca_state != TCP_CA_Open &&

            icsk->icsk_ca_state != TCP_CA_Disorder) {

                ca->packetcount = 0;

                ca->lasttime = now;

                return;

        }

        ca->packetcount += pkts_acked;

        if (ca->packetcount >= tp->snd_cwnd - (ca->alpha >> 7 ? : 1)

            && now - ca->lasttime >= ca->minRTT

            && ca->minRTT > 0) {

                __u32 cur_Bi = ca->packetcount * HZ / (now - ca->lasttime);

                if (htcp_ccount(ca) <= 3) {

                        /* just after backoff */

                        ca->minB = ca->maxB = ca->Bi = cur_Bi;

                } else {

                        ca->Bi = (3 * ca->Bi + cur_Bi) / 4;

                        if (ca->Bi > ca->maxB)

                                ca->maxB = ca->Bi;

                        if (ca->minB > ca->maxB)

                                ca->minB = ca->maxB;

                }

                ca->packetcount = 0;

                ca->lasttime = now;

        }

}

static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)

{

        if (use_bandwidth_switch) {

                u32 maxB = ca->maxB;

                u32 old_maxB = ca->old_maxB;

                ca->old_maxB = ca->maxB;

                if (!between(5 * maxB, 4 * old_maxB, 6 * old_maxB)) {

                        ca->beta = BETA_MIN;

                        ca->modeswitch = 0;

                        return;

                }

        }

        if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {

                ca->beta = (minRTT << 7) / maxRTT;

                if (ca->beta < BETA_MIN)

                        ca->beta = BETA_MIN;

                else if (ca->beta > BETA_MAX)

                        ca->beta = BETA_MAX;

        } else {

                ca->beta = BETA_MIN;

                ca->modeswitch = 1;

        }

}

static inline void htcp_alpha_update(struct htcp *ca)

{

        u32 minRTT = ca->minRTT;

        u32 factor = 1;

        u32 diff = htcp_cong_time(ca);

        if (diff > HZ) {

                diff -= HZ;

                factor = 1 + (10 * diff + ((diff / 2) * (diff / 2) / HZ)) / HZ;

        }

        if (use_rtt_scaling && minRTT) {

                u32 scale = (HZ << 3) / (10 * minRTT);

                /* clamping ratio to interval [0.5,10]<<3 */

                scale = min(max(scale, 1U << 2), 10U << 3);

                factor = (factor << 3) / scale;

                if (!factor)

                        factor = 1;

        }

        ca->alpha = 2 * factor * ((1 << 7) - ca->beta);

        if (!ca->alpha)

                ca->alpha = ALPHA_BASE;

}

/*

 * After we have the rtt data to calculate beta, we'd still prefer to wait one

 * rtt before we adjust our beta to ensure we are working from a consistent

 * data.

 *

 * This function should be called when we hit a congestion event since only at

 * that point do we really have a real sense of maxRTT (the queues en route

 * were getting just too full now).

 */

static void htcp_param_update(struct sock *sk)

{

        struct htcp *ca = inet_csk_ca(sk);

        u32 minRTT = ca->minRTT;

        u32 maxRTT = ca->maxRTT;

        htcp_beta_update(ca, minRTT, maxRTT);

        htcp_alpha_update(ca);

        /* add slowly fading memory for maxRTT to accommodate routing changes */

        if (minRTT > 0 && maxRTT > minRTT)

                ca->maxRTT = minRTT + ((maxRTT - minRTT) * 95) / 100;

}

static u32 htcp_recalc_ssthresh(struct sock *sk)

{

        const struct tcp_sock *tp = tcp_sk(sk);

        const struct htcp *ca = inet_csk_ca(sk);

        htcp_param_update(sk);

        return max((tp->snd_cwnd * ca->beta) >> 7, 2U);

}

static void htcp_cong_avoid(struct sock *sk, u32 ack,

                            u32 in_flight, int data_acked)

{

        struct tcp_sock *tp = tcp_sk(sk);

        struct htcp *ca = inet_csk_ca(sk);

        if (!tcp_is_cwnd_limited(sk, in_flight))

                return;

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

                tcp_slow_start(tp);

        else {

                /* In dangerous area, increase slowly.

                 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd

                 */

                if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {

                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)

                                tp->snd_cwnd++;

                        tp->snd_cwnd_cnt = 0;

                        htcp_alpha_update(ca);

                } else

                        tp->snd_cwnd_cnt += ca->pkts_acked;

                ca->pkts_acked = 1;

        }

}

static void htcp_init(struct sock *sk)

{

        struct htcp *ca = inet_csk_ca(sk);

        memset(ca, 0, sizeof(struct htcp));

        ca->alpha = ALPHA_BASE;

        ca->beta = BETA_MIN;

        ca->pkts_acked = 1;

        ca->last_cong = jiffies;

}

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

{

        switch (new_state) {

        case TCP_CA_Open:

                {

                        struct htcp *ca = inet_csk_ca(sk);

                        ca->last_cong = jiffies;

                }

                break;

        case TCP_CA_CWR:

        case TCP_CA_Recovery:

        case TCP_CA_Loss:

                htcp_reset(inet_csk_ca(sk));

                break;

        }

}

static struct tcp_congestion_ops htcp = {

        .init           = htcp_init,

        .ssthresh       = htcp_recalc_ssthresh,

        .cong_avoid     = htcp_cong_avoid,

        .set_state      = htcp_state,

        .undo_cwnd      = htcp_cwnd_undo,

        .pkts_acked     = measure_achieved_throughput,

        .owner          = THIS_MODULE,

        .name           = "htcp",

};

static int __init htcp_register(void)

{

        BUILD_BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);

        BUILD_BUG_ON(BETA_MIN >= BETA_MAX);

        return tcp_register_congestion_control(&htcp);

}

static void __exit htcp_unregister(void)

{

        tcp_unregister_congestion_control(&htcp);

}

module_init(htcp_register);

module_exit(htcp_unregister);

MODULE_AUTHOR("Baruch Even");

MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("H-TCP");