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/* Tom Kelly's Scalable TCP

 *

 * See htt://www-lce.eng.cam.ac.uk/~ctk21/scalable/

 *

 * John Heffner <jheffner@sc.edu>

 */

#include <linux/module.h>

#include <net/tcp.h>

/* These factors derived from the recommended values in the aer:

 * .01 and and 7/8. We use 50 instead of 100 to account for

 * delayed ack.

 */

#define TCP_SCALABLE_AI_CNT     50U

#define TCP_SCALABLE_MD_SCALE   3

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

                                    u32 in_flight, int flag)

{

        struct tcp_sock *tp = tcp_sk(sk);

        if (!tcp_is_cwnd_limited(sk, in_flight))

                return;

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

                tcp_slow_start(tp);

        else {

                tp->snd_cwnd_cnt++;

                if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){

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

                                tp->snd_cwnd++;

                        tp->snd_cwnd_cnt = 0;

                }

        }

}

static u32 tcp_scalable_ssthresh(struct sock *sk)

{

        const struct tcp_sock *tp = tcp_sk(sk);

        return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);

}

static struct tcp_congestion_ops tcp_scalable = {

        .ssthresh       = tcp_scalable_ssthresh,

        .cong_avoid     = tcp_scalable_cong_avoid,

        .min_cwnd       = tcp_reno_min_cwnd,

        .owner          = THIS_MODULE,

        .name           = "scalable",

};

static int __init tcp_scalable_register(void)

{

        return tcp_register_congestion_control(&tcp_scalable);

}

static void __exit tcp_scalable_unregister(void)

{

        tcp_unregister_congestion_control(&tcp_scalable);

}

module_init(tcp_scalable_register);

module_exit(tcp_scalable_unregister);

MODULE_AUTHOR("John Heffner");

MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("Scalable TCP");