/*
* 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.
* http://www.hamilton.ie/net/htcp3.pdf
*/
#include <linux/config.h>
#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 = 1;
module_param(use_rtt_scaling, int, 0644);
MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
static int use_bandwidth_switch = 1;
module_param(use_bandwidth_switch, int, 0644);
MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
struct htcp {
u16 alpha; /* Fixed point arith, << 7 */
u8 beta; /* Fixed point arith, << 7 */
u8 modeswitch; /* Delay modeswitch until we had at least one congestion event */
u8 ccount; /* Number of RTTs since last congestion event */
u8 undo_ccount;
u16 packetcount;
u32 minRTT;
u32 maxRTT;
u32 snd_cwnd_cnt2;
u32 undo_maxRTT;
u32 undo_old_maxB;
/* Bandwidth estimation */
u32 minB;
u32 maxB;
u32 old_maxB;
u32 Bi;
u32 lasttime;
};
static inline void htcp_reset(struct htcp *ca)
{
ca->undo_ccount = ca->ccount;
ca->undo_maxRTT = ca->maxRTT;
ca->undo_old_maxB = ca->old_maxB;
ca->ccount = 0;
ca->snd_cwnd_cnt2 = 0;
}
static u32 htcp_cwnd_undo(struct tcp_sock *tp)
{
struct htcp *ca = tcp_ca(tp);
ca->ccount = ca->undo_ccount;
ca->maxRTT = ca->undo_maxRTT;
ca->old_maxB = ca->undo_old_maxB;
return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);
}
static inline void measure_rtt(struct tcp_sock *tp)
{
struct htcp *ca = tcp_ca(tp);
u32 srtt = tp->srtt>>3;
/* 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 (tp->ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && ca->ccount > 3) {
if (ca->maxRTT < ca->minRTT)
ca->maxRTT = ca->minRTT;
if (ca->maxRTT < srtt && srtt <= ca->maxRTT+HZ/50)
ca->maxRTT = srtt;
}
}
static void measure_achieved_throughput(struct tcp_sock *tp, u32 pkts_acked)
{
struct htcp *ca = tcp_ca(tp);
u32 now = tcp_time_stamp;
/* achieved throughput calculations */
if (tp->ca_state != TCP_CA_Open && tp->ca_state != TCP_CA_Disorder) {
ca->packetcount = 0;
ca->lasttime = now;
return;
}
ca->packetcount += pkts_acked;
if (ca->packetcount >= tp->snd_cwnd - (ca->alpha>>7? : 1)
&& now - ca->lasttime >= ca->minRTT
&& ca->minRTT > 0) {
__u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);
if (ca->ccount <= 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 > max(HZ/100, 1) && 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 = ca->ccount * minRTT; /* time since last backoff */
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);
scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to interval [0.5,10]<<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 tcp_sock *tp)
{
struct htcp *ca = tcp_ca(tp);
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 etc */
if (minRTT > 0 && maxRTT > minRTT)
ca->maxRTT = minRTT + ((maxRTT-minRTT)*95)/100;
}
static u32 htcp_recalc_ssthresh(struct tcp_sock *tp)
{
struct htcp *ca = tcp_ca(tp);
htcp_param_update(tp);
return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
}
static void htcp_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,
u32 in_flight, int data_acked)
{
struct htcp *ca = tcp_ca(tp);
if (in_flight < tp->snd_cwnd)
return;
if (tp->snd_cwnd <= tp->snd_ssthresh) {
/* In "safe" area, increase. */
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
} else {
measure_rtt(tp);
/* keep track of number of round-trip times since last backoff event */
if (ca->snd_cwnd_cnt2++ > tp->snd_cwnd) {
ca->ccount++;
ca->snd_cwnd_cnt2 = 0;
htcp_alpha_update(ca);
}
/* In dangerous area, increase slowly.
* In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
*/
if ((tp->snd_cwnd_cnt++ * ca->alpha)>>7 >= tp->snd_cwnd) {
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
tp->snd_cwnd_cnt = 0;
ca->ccount++;
}
}
}
/* Lower bound on congestion window. */
static u32 htcp_min_cwnd(struct tcp_sock *tp)
{
return tp->snd_ssthresh;
}
static void htcp_init(struct tcp_sock *tp)
{
struct htcp *ca = tcp_ca(tp);
memset(ca, 0, sizeof(struct htcp));
ca->alpha = ALPHA_BASE;
ca->beta = BETA_MIN;
}
static void htcp_state(struct tcp_sock *tp, u8 new_state)
{
switch (new_state) {
case TCP_CA_CWR:
case TCP_CA_Recovery:
case TCP_CA_Loss:
htcp_reset(tcp_ca(tp));
break;
}
}
static struct tcp_congestion_ops htcp = {
.init = htcp_init,
.ssthresh = htcp_recalc_ssthresh,
.min_cwnd = htcp_min_cwnd,
.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)
{
BUG_ON(sizeof(struct htcp) > TCP_CA_PRIV_SIZE);
BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
if (!use_bandwidth_switch)
htcp.pkts_acked = NULL;
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");
