// SPDX-License-Identifier: GPL-2.0-only
/*
* 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.
* https://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)
{
struct htcp *ca = inet_csk_ca(sk);
if (ca->undo_last_cong) {
ca->last_cong = ca->undo_last_cong;
ca->maxRTT = ca->undo_maxRTT;
ca->old_maxB = ca->undo_old_maxB;
ca->undo_last_cong = 0;
}
return tcp_reno_undo_cwnd(sk);
}
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,
const struct ack_sample *sample)
{
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_jiffies32;
if (icsk->icsk_ca_state == TCP_CA_Open)
ca->pkts_acked = sample->pkts_acked;
if (sample->rtt_us > 0)
measure_rtt(sk, usecs_to_jiffies(sample->rtt_us));
if (!use_bandwidth_switch)
return;
/* achieved throughput calculations */
if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_Disorder))) {
ca->packetcount = 0;
ca->lasttime = now;
return;
}
ca->packetcount += sample->pkts_acked;
if (ca->packetcount >= tcp_snd_cwnd(tp) - (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 = clamp(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((tcp_snd_cwnd(tp) * ca->beta) >> 7, 2U);
}
static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
struct tcp_sock *tp = tcp_sk(sk);
struct htcp *ca = inet_csk_ca(sk);
if (!tcp_is_cwnd_limited(sk))
return;
if (tcp_in_slow_start(tp))
tcp_slow_start(tp, acked);
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 >= tcp_snd_cwnd(tp)) {
if (tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp)
tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
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);
if (ca->undo_last_cong) {
ca->last_cong = jiffies;
ca->undo_last_cong = 0;
}
}
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 __read_mostly = {
.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");
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