// SPDX-License-Identifier: GPL-2.0-only
/*
* Sally Floyd's High Speed TCP (RFC 3649) congestion control
*
* See http://www.icir.org/floyd/hstcp.html
*
* John Heffner <jheffner@psc.edu>
*/
#include <linux/module.h>
#include <net/tcp.h>
/* From AIMD tables from RFC 3649 appendix B,
* with fixed-point MD scaled <<8.
*/
static const 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 ARRAY_SIZE(hstcp_aimd_vals)
struct hstcp {
u32 ai;
};
static void hstcp_init(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct hstcp *ca = inet_csk_ca(sk);
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 sock *sk, u32 ack, u32 acked)
{
struct tcp_sock *tp = tcp_sk(sk);
struct hstcp *ca = inet_csk_ca(sk);
if (!tcp_is_cwnd_limited(sk))
return;
if (tcp_in_slow_start(tp))
tcp_slow_start(tp, acked);
else {
/* Update AIMD parameters.
*
* We want to guarantee that:
* hstcp_aimd_vals[ca->ai-1].cwnd <
* snd_cwnd <=
* hstcp_aimd_vals[ca->ai].cwnd
*/
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 - 1)
ca->ai++;
} else if (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd) {
while (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd)
ca->ai--;
}
/* Do additive increase */
if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
/* cwnd = cwnd + a(w) / cwnd */
tp->snd_cwnd_cnt += ca->ai + 1;
if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
tp->snd_cwnd_cnt -= tp->snd_cwnd;
tp->snd_cwnd++;
}
}
}
}
static u32 hstcp_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct hstcp *ca = inet_csk_ca(sk);
/* Do multiplicative decrease */
return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
}
static struct tcp_congestion_ops tcp_highspeed __read_mostly = {
.init = hstcp_init,
.ssthresh = hstcp_ssthresh,
.undo_cwnd = tcp_reno_undo_cwnd,
.cong_avoid = hstcp_cong_avoid,
.owner = THIS_MODULE,
.name = "highspeed"
};
static int __init hstcp_register(void)
{
BUILD_BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE);
return tcp_register_congestion_control(&tcp_highspeed);
}
static void __exit hstcp_unregister(void)
{
tcp_unregister_congestion_control(&tcp_highspeed);
}
module_init(hstcp_register);
module_exit(hstcp_unregister);
MODULE_AUTHOR("John Heffner");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("High Speed TCP");
