root/net/ipv4/tcp_scalable.c

DEFINITIONS

1. tcp_scalable_cong_avoid
2. tcp_scalable_ssthresh
3. tcp_scalable_register
4. tcp_scalable_unregister

/* 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)
{
        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");