/*
* Binary Increase Congestion control for TCP
*
* This is from the implementation of BICTCP in
* Lison-Xu, Kahaled Harfoush, and Injong Rhee.
* "Binary Increase Congestion Control for Fast, Long Distance
* Networks" in InfoComm 2004
* Available from:
* http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
*
* Unless BIC is enabled and congestion window is large
* this behaves the same as the original Reno.
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <net/tcp.h>
#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
* max_cwnd = snd_cwnd * beta
*/
#define BICTCP_B 4 /*
* In binary search,
* go to point (max+min)/N
*/
static int fast_convergence = 1;
static int max_increment = 16;
static int low_window = 14;
static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
static int initial_ssthresh = 100;
static int smooth_part = 20;
module_param(fast_convergence, int, 0644);
MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
module_param(max_increment, int, 0644);
MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
module_param(low_window, int, 0644);
MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
module_param(beta, int, 0644);
MODULE_PARM_DESC(beta, "beta for multiplicative increase");
module_param(initial_ssthresh, int, 0644);
MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
module_param(smooth_part, int, 0644);
MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
/* BIC TCP Parameters */
struct bictcp {
u32 cnt; /* increase cwnd by 1 after ACKs */
u32 last_max_cwnd; /* last maximum snd_cwnd */
u32 loss_cwnd; /* congestion window at last loss */
u32 last_cwnd; /* the last snd_cwnd */
u32 last_time; /* time when updated last_cwnd */
u32 epoch_start; /* beginning of an epoch */
#define ACK_RATIO_SHIFT 4
u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
};
static inline void bictcp_reset(struct bictcp *ca)
{
ca->cnt = 0;
ca->last_max_cwnd = 0;
ca->loss_cwnd = 0;
ca->last_cwnd = 0;
ca->last_time = 0;
ca->epoch_start = 0;
ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
}
static void bictcp_init(struct sock *sk)
{
bictcp_reset(inet_csk_ca(sk));
if (initial_ssthresh)
tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
}
/*
* Compute congestion window to use.
*/
static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
{
if (ca->last_cwnd == cwnd &&
(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
return;
ca->last_cwnd = cwnd;
ca->last_time = tcp_time_stamp;
if (ca->epoch_start == 0) /* record the beginning of an epoch */
ca->epoch_start = tcp_time_stamp;
/* start off normal */
if (cwnd <= low_window) {
ca->cnt = cwnd;
return;
}
/* binary increase */
if (cwnd < ca->last_max_cwnd) {
__u32 dist = (ca->last_max_cwnd - cwnd)
/ BICTCP_B;
if (dist > max_increment)
/* linear increase */
ca->cnt = cwnd / max_increment;
else if (dist <= 1U)
/* binary search increase */
ca->cnt = (cwnd * smooth_part) / BICTCP_B;
else
/* binary search increase */
ca->cnt = cwnd / dist;
} else {
/* slow start AMD linear increase */
if (cwnd < ca->last_max_cwnd + BICTCP_B)
/* slow start */
ca->cnt = (cwnd * smooth_part) / BICTCP_B;
else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
/* slow start */
ca->cnt = (cwnd * (BICTCP_B-1))
/ (cwnd - ca->last_max_cwnd);
else
/* linear increase */
ca->cnt = cwnd / max_increment;
}
/* if in slow start or link utilization is very low */
if (ca->loss_cwnd == 0) {
if (ca->cnt > 20) /* increase cwnd 5% per RTT */
ca->cnt = 20;
}
ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
if (ca->cnt == 0) /* cannot be zero */
ca->cnt = 1;
}
static void bictcp_cong_avoid(struct sock *sk, u32 ack,
u32 seq_rtt, u32 in_flight, int data_acked)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bictcp *ca = inet_csk_ca(sk);
if (!tcp_is_cwnd_limited(sk, in_flight))
return;
if (tp->snd_cwnd <= tp->snd_ssthresh)
tcp_slow_start(tp);
else {
bictcp_update(ca, tp->snd_cwnd);
/* In dangerous area, increase slowly.
* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
*/
if (tp->snd_cwnd_cnt >= ca->cnt) {
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
tp->snd_cwnd_cnt = 0;
} else
tp->snd_cwnd_cnt++;
}
}
/*
* behave like Reno until low_window is reached,
* then increase congestion window slowly
*/
static u32 bictcp_recalc_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct bictcp *ca = inet_csk_ca(sk);
ca->epoch_start = 0; /* end of epoch */
/* Wmax and fast convergence */
if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
/ (2 * BICTCP_BETA_SCALE);
else
ca->last_max_cwnd = tp->snd_cwnd;
ca->loss_cwnd = tp->snd_cwnd;
if (tp->snd_cwnd <= low_window)
return max(tp->snd_cwnd >> 1U, 2U);
else
return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
}
static u32 bictcp_undo_cwnd(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct bictcp *ca = inet_csk_ca(sk);
return max(tp->snd_cwnd, ca->last_max_cwnd);
}
static void bictcp_state(struct sock *sk, u8 new_state)
{
if (new_state == TCP_CA_Loss)
bictcp_reset(inet_csk_ca(sk));
}
/* Track delayed acknowledgment ratio using sliding window
* ratio = (15*ratio + sample) / 16
*/
static void bictcp_acked(struct sock *sk, u32 cnt)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
struct bictcp *ca = inet_csk_ca(sk);
cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
ca->delayed_ack += cnt;
}
}
static struct tcp_congestion_ops bictcp = {
.init = bictcp_init,
.ssthresh = bictcp_recalc_ssthresh,
.cong_avoid = bictcp_cong_avoid,
.set_state = bictcp_state,
.undo_cwnd = bictcp_undo_cwnd,
.pkts_acked = bictcp_acked,
.owner = THIS_MODULE,
.name = "bic",
};
static int __init bictcp_register(void)
{
BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
return tcp_register_congestion_control(&bictcp);
}
static void __exit bictcp_unregister(void)
{
tcp_unregister_congestion_control(&bictcp);
}
module_init(bictcp_register);
module_exit(bictcp_unregister);
MODULE_AUTHOR("Stephen Hemminger");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("BIC TCP");
