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Re: [RFC] TCP congestion schedulers

To: Stephen Hemminger <shemminger@xxxxxxxx>
Subject: Re: [RFC] TCP congestion schedulers
From: John Heffner <jheffner@xxxxxxx>
Date: Tue, 15 Mar 2005 14:54:24 -0500 (EST)
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>, baruch@xxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <20050314151726.532af90d@xxxxxxxxxxxxxxxxx>
References: <421CF5E5.1060606@xxxxxxxxx> <20050223135732.39e62c6c.davem@xxxxxxxxxxxxx> <421D1E66.5090301@xxxxxxxx> <421D30FA.1060900@xxxxxxxxx> <20050225120814.5fa77b13@xxxxxxxxxxxxxxxxx> <20050309210442.3e9786a6.davem@xxxxxxxxxxxxx> <4230288F.1030202@xxxxxxxxx> <20050310182629.1eab09ec.davem@xxxxxxxxxxxxx> <20050311120054.4bbf675a@xxxxxxxxxxxxxxxxx> <20050311201011.360c00da.davem@xxxxxxxxxxxxx> <20050314151726.532af90d@xxxxxxxxxxxxxxxxx>
Sender: netdev-bounce@xxxxxxxxxxx
Cool. :)  Here's High Speed TCP.

  -John


---

/*
 * Sally Floyd's High Speed TCP (RFC 3649) congestion control
 *
 * See http://www.icir.org/floyd/hstcp.html
 *
 * John Heffner <jheffner@xxxxxxx>
 */

#include <linux/config.h>
#include <linux/module.h>
#include <net/tcp.h>


/* From AIMD tables from RFC 3649 appendix B,
 * with fixed-point MD scaled <<8.
 */
static struct hstcp_aimd_val {
        unsigned int cwnd;
        unsigned int md;
} hstcp_aimd_vals[] = {
 {     38,  128, /*  0.50 */ },
 {    118,  112, /*  0.44 */ },
 {    221,  104, /*  0.41 */ },
 {    347,   98, /*  0.38 */ },
 {    495,   93, /*  0.37 */ },
 {    663,   89, /*  0.35 */ },
 {    851,   86, /*  0.34 */ },
 {   1058,   83, /*  0.33 */ },
 {   1284,   81, /*  0.32 */ },
 {   1529,   78, /*  0.31 */ },
 {   1793,   76, /*  0.30 */ },
 {   2076,   74, /*  0.29 */ },
 {   2378,   72, /*  0.28 */ },
 {   2699,   71, /*  0.28 */ },
 {   3039,   69, /*  0.27 */ },
 {   3399,   68, /*  0.27 */ },
 {   3778,   66, /*  0.26 */ },
 {   4177,   65, /*  0.26 */ },
 {   4596,   64, /*  0.25 */ },
 {   5036,   62, /*  0.25 */ },
 {   5497,   61, /*  0.24 */ },
 {   5979,   60, /*  0.24 */ },
 {   6483,   59, /*  0.23 */ },
 {   7009,   58, /*  0.23 */ },
 {   7558,   57, /*  0.22 */ },
 {   8130,   56, /*  0.22 */ },
 {   8726,   55, /*  0.22 */ },
 {   9346,   54, /*  0.21 */ },
 {   9991,   53, /*  0.21 */ },
 {  10661,   52, /*  0.21 */ },
 {  11358,   52, /*  0.20 */ },
 {  12082,   51, /*  0.20 */ },
 {  12834,   50, /*  0.20 */ },
 {  13614,   49, /*  0.19 */ },
 {  14424,   48, /*  0.19 */ },
 {  15265,   48, /*  0.19 */ },
 {  16137,   47, /*  0.19 */ },
 {  17042,   46, /*  0.18 */ },
 {  17981,   45, /*  0.18 */ },
 {  18955,   45, /*  0.18 */ },
 {  19965,   44, /*  0.17 */ },
 {  21013,   43, /*  0.17 */ },
 {  22101,   43, /*  0.17 */ },
 {  23230,   42, /*  0.17 */ },
 {  24402,   41, /*  0.16 */ },
 {  25618,   41, /*  0.16 */ },
 {  26881,   40, /*  0.16 */ },
 {  28193,   39, /*  0.16 */ },
 {  29557,   39, /*  0.15 */ },
 {  30975,   38, /*  0.15 */ },
 {  32450,   38, /*  0.15 */ },
 {  33986,   37, /*  0.15 */ },
 {  35586,   36, /*  0.14 */ },
 {  37253,   36, /*  0.14 */ },
 {  38992,   35, /*  0.14 */ },
 {  40808,   35, /*  0.14 */ },
 {  42707,   34, /*  0.13 */ },
 {  44694,   33, /*  0.13 */ },
 {  46776,   33, /*  0.13 */ },
 {  48961,   32, /*  0.13 */ },
 {  51258,   32, /*  0.13 */ },
 {  53677,   31, /*  0.12 */ },
 {  56230,   30, /*  0.12 */ },
 {  58932,   30, /*  0.12 */ },
 {  61799,   29, /*  0.12 */ },
 {  64851,   28, /*  0.11 */ },
 {  68113,   28, /*  0.11 */ },
 {  71617,   27, /*  0.11 */ },
 {  75401,   26, /*  0.10 */ },
 {  79517,   26, /*  0.10 */ },
 {  84035,   25, /*  0.10 */ },
 {  89053,   24, /*  0.10 */ },
};

#define HSTCP_AIMD_MAX  ((sizeof (hstcp_aimd_vals) / sizeof (struct 
hstcp_aimd_val)) - 1)

struct hstcp_ca {
        u32     ai;
};

static void hstcp_start(struct tcp_sock *tp)
{
        struct hstcp_ca *ca = tcp_ca(tp);

        ca->ai = 0;

        /* Ensure the MD arithmetic works.  This is somewhat pedantic,
         * since I don't think we will see a cwnd this large. :) */
        tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
}

static void hstcp_cong_avoid(struct tcp_sock *tp, u32 adk, u32 rtt, u32 
in_flight)
{
        struct hstcp_ca *ca = tcp_ca(tp);

        if (in_flight < tp->snd_cwnd)
                return;

        if (tp->snd_cwnd <= tp->snd_ssthresh) {
                if (tp->snd_cwnd < tp->snd_cwnd_clamp)
                        tp->snd_cwnd++;
        } else {
                /* Update AIMD parameters */
                if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
                        while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
                               ca->ai < HSTCP_AIMD_MAX)
                                ca->ai++;
                } else if (tp->snd_cwnd < hstcp_aimd_vals[ca->ai].cwnd) {
                        while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
                               ca->ai > 0)
                                ca->ai--;
                }

                /* Do additive increase */
                if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
                        tp->snd_cwnd_cnt += ca->ai;
                        if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
                                tp->snd_cwnd++;
                                tp->snd_cwnd_cnt -= tp->snd_cwnd;
                        }
                }
        }
}

static u32 hstcp_ssthresh(struct tcp_sock *tp)
{
        struct hstcp_ca *ca = tcp_ca(tp);

        /* Do multiplicative decrease */
        return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) 
>> 8), 2U);
}

static struct tcp_ca_type tcp_highspeed = {
        .start          = hstcp_start,
        .ssthresh       = hstcp_ssthresh,
        .min_cwnd       = tcp_reno_cwnd_min,
        .cong_avoid     = hstcp_cong_avoid,

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

static int __init hstcp_init(void)
{
        BUILD_BUG_ON(sizeof(struct hstcp_ca) > TCP_CA_PRIV_SIZE);
        tcp_ca_register(&tcp_highspeed);
        return 0;
}

static void __exit hstcp_exit(void)
{
        tcp_ca_unregister(&tcp_highspeed);
}

module_init(hstcp_init);
module_exit(hstcp_exit);

MODULE_AUTHOR("John Heffner");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("High Speed TCP");


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