/*
* TCP Illinois congestion control.
* Home page:
* http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html
*
* The algorithm is described in:
* "TCP-Illinois: A Loss and Delay-Based Congestion Control Algorithm
* for High-Speed Networks"
* http://www.ews.uiuc.edu/~shaoliu/papersandslides/liubassri06perf.pdf
*
* Implemented from description in paper and ns-2 simulation.
* Copyright (C) 2007 Stephen Hemminger <shemminger@linux-foundation.org>
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>
#include <asm/div64.h>
#include <net/tcp.h>
#define ALPHA_SHIFT 7
#define ALPHA_SCALE (1u<<ALPHA_SHIFT)
#define ALPHA_MIN ((3*ALPHA_SCALE)/10) /* ~0.3 */
#define ALPHA_MAX (10*ALPHA_SCALE) /* 10.0 */
#define ALPHA_BASE ALPHA_SCALE /* 1.0 */
#define BETA_SHIFT 6
#define BETA_SCALE (1u<<BETA_SHIFT)
#define BETA_MIN (BETA_SCALE/8) /* 0.8 */
#define BETA_MAX (BETA_SCALE/2)
#define BETA_BASE BETA_MAX /* 0.5 */
#define THETA 5
static int win_thresh __read_mostly = 15;
module_param(win_thresh, int, 0644);
MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing");
#define MAX_RTT 0x7fffffff
/* TCP Illinois Parameters */
struct tcp_illinois {
u32 last_alpha;
u32 min_rtt;
u32 max_rtt;
u32 rtt_low;
u32 rtt_cnt;
u64 sum_rtt;
};
static void tcp_illinois_init(struct sock *sk)
{
struct tcp_illinois *ca = inet_csk_ca(sk);
ca->last_alpha = ALPHA_BASE;
ca->min_rtt = 0x7fffffff;
}
/*
* Keep track of min, max and average RTT
*/
static void tcp_illinois_rtt_calc(struct sock *sk, u32 rtt)
{
struct tcp_illinois *ca = inet_csk_ca(sk);
if (rtt < ca->min_rtt)
ca->min_rtt = rtt;
if (rtt > ca->max_rtt)
ca->max_rtt = rtt;
if (++ca->rtt_cnt == 1)
ca->sum_rtt = rtt;
else
ca->sum_rtt += rtt;
}
/* max queuing delay */
static inline u32 max_delay(const struct tcp_illinois *ca)
{
return ca->max_rtt - ca->min_rtt;
}
/* average queueing delay */
static u32 avg_delay(struct tcp_illinois *ca)
{
u64 avg_rtt = ca->sum_rtt;
do_div(avg_rtt, ca->rtt_cnt);
ca->sum_rtt = 0;
ca->rtt_cnt = 0;
return avg_rtt - ca->min_rtt;
}
/*
* Compute value of alpha used for additive increase.
* If small window then use 1.0, equivalent to Reno.
*
* For larger windows, adjust based on average delay.
* A. If average delay is at minimum (we are uncongested),
* then use large alpha (10.0) to increase faster.
* B. If average delay is at maximum (getting congested)
* then use small alpha (1.0)
*
* The result is a convex window growth curve.
*/
static u32 alpha(const struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_illinois *ca = inet_csk_ca(sk);
u32 dm = max_delay(ca);
u32 da = avg_delay(ca);
u32 d1, a;
if (tp->snd_cwnd < win_thresh)
return ALPHA_BASE; /* same as Reno (1.0) */
d1 = dm / 100;
if (da <= d1) {
/* Don't let noise force agressive response */
if (ca->rtt_low < THETA) {
++ca->rtt_low;
return ca->last_alpha;
} else
return ALPHA_MAX;
}
ca->rtt_low = 0;
/*
* Based on:
*
* (dm - d1) amin amax
* k1 = -------------------
* amax - amin
*
* (dm - d1) amin
* k2 = ---------------- - d1
* amax - amin
*
* k1
* alpha = ----------
* k2 + da
*/
dm -= d1;
da -= d1;
a = (dm * ALPHA_MAX) / (dm - (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
ca->last_alpha = a;
return a;
}
/*
* Increase window in response to successful acknowledgment.
*/
static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
u32 in_flight, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
/* RFC2861 only increase cwnd if fully utilized */
if (!tcp_is_cwnd_limited(sk, in_flight))
return;
/* In slow start */
if (tp->snd_cwnd <= tp->snd_ssthresh)
tcp_slow_start(tp);
else {
/* additive increase cwnd += alpha / cwnd */
if ((tp->snd_cwnd_cnt * alpha(sk)) >> ALPHA_SHIFT >= tp->snd_cwnd) {
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
tp->snd_cwnd_cnt = 0;
} else
tp->snd_cwnd_cnt++;
}
}
/*
* Beta used for multiplicative decrease.
* For small window sizes returns same value as Reno (0.5)
*
* If delay is small (10% of max) then beta = 1/8
* If delay is up to 80% of max then beta = 1/2
* In between is a linear function
*/
static inline u32 beta(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_illinois *ca = inet_csk_ca(sk);
u32 dm = max_delay(ca);
u32 da = avg_delay(ca);
u32 d2, d3;
if (tp->snd_cwnd < win_thresh)
return BETA_BASE;
d2 = dm / 10;
if (da <= d2)
return BETA_MIN;
d3 = (8 * dm) / 10;
if (da >= d3 || d3 <= d2)
return BETA_MAX;
/*
* Based on:
*
* bmin d3 - bmax d2
* k3 = -------------------
* d3 - d2
*
* bmax - bmin
* k4 = -------------
* d3 - d2
*
* b = k3 + k4 da
*/
return (BETA_MIN * d3 - BETA_MAX * d2 + (BETA_MAX - BETA_MIN) * da)
/ (d3 - d2);
}
static u32 tcp_illinois_ssthresh(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Multiplicative decrease */
return max((tp->snd_cwnd * beta(sk)) >> BETA_SHIFT, 2U);
}
/* Extract info for TCP socket info provided via netlink.
* We aren't really doing Vegas, but we can provide RTT info
*/
static void tcp_illinois_get_info(struct sock *sk, u32 ext,
struct sk_buff *skb)
{
const struct tcp_illinois *ca = inet_csk_ca(sk);
if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
struct tcpvegas_info info = {
.tcpv_enabled = 1,
.tcpv_rttcnt = ca->rtt_cnt,
.tcpv_minrtt = ca->min_rtt,
};
u64 avg_rtt = ca->sum_rtt;
do_div(avg_rtt, ca->rtt_cnt);
info.tcpv_rtt = avg_rtt;
nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
}
}
static struct tcp_congestion_ops tcp_illinois = {
.init = tcp_illinois_init,
.ssthresh = tcp_illinois_ssthresh,
.min_cwnd = tcp_reno_min_cwnd,
.cong_avoid = tcp_illinois_cong_avoid,
.rtt_sample = tcp_illinois_rtt_calc,
.get_info = tcp_illinois_get_info,
.owner = THIS_MODULE,
.name = "illinois",
};
static int __init tcp_illinois_register(void)
{
BUILD_BUG_ON(sizeof(struct tcp_illinois) > ICSK_CA_PRIV_SIZE);
return tcp_register_congestion_control(&tcp_illinois);
}
static void __exit tcp_illinois_unregister(void)
{
tcp_unregister_congestion_control(&tcp_illinois);
}
module_init(tcp_illinois_register);
module_exit(tcp_illinois_unregister);
MODULE_AUTHOR("Stephen Hemminger, Shao Liu");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Illinois");
MODULE_VERSION("0.3");
