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DEFINITIONS
This source file includes following definitions.
- rtt_reset
- tcp_illinois_init
- tcp_illinois_acked
- max_delay
- avg_delay
- alpha
- beta
- update_params
- tcp_illinois_state
- tcp_illinois_cong_avoid
- tcp_illinois_ssthresh
- tcp_illinois_info
- tcp_illinois_register
- tcp_illinois_unregister
/*
* 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 U32_MAX ((u32)~0U)
#define RTT_MAX (U32_MAX / ALPHA_MAX) /* 3.3 secs */
#define BETA_SHIFT 6
#define BETA_SCALE (1u<<BETA_SHIFT)
#define BETA_MIN (BETA_SCALE/8) /* 0.125 */
#define BETA_MAX (BETA_SCALE/2) /* 0.5 */
#define BETA_BASE BETA_MAX
static int win_thresh __read_mostly = 15;
module_param(win_thresh, int, 0);
MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing");
static int theta __read_mostly = 5;
module_param(theta, int, 0);
MODULE_PARM_DESC(theta, "# of fast RTT's before full growth");
/* TCP Illinois Parameters */
struct illinois {
u64 sum_rtt; /* sum of rtt's measured within last rtt */
u16 cnt_rtt; /* # of rtts measured within last rtt */
u32 base_rtt; /* min of all rtt in usec */
u32 max_rtt; /* max of all rtt in usec */
u32 end_seq; /* right edge of current RTT */
u32 alpha; /* Additive increase */
u32 beta; /* Muliplicative decrease */
u16 acked; /* # packets acked by current ACK */
u8 rtt_above; /* average rtt has gone above threshold */
u8 rtt_low; /* # of rtts measurements below threshold */
};
static void rtt_reset(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
ca->end_seq = tp->snd_nxt;
ca->cnt_rtt = 0;
ca->sum_rtt = 0;
/* TODO: age max_rtt? */
}
static void tcp_illinois_init(struct sock *sk)
{
struct illinois *ca = inet_csk_ca(sk);
ca->alpha = ALPHA_MAX;
ca->beta = BETA_BASE;
ca->base_rtt = 0x7fffffff;
ca->max_rtt = 0;
ca->acked = 0;
ca->rtt_low = 0;
ca->rtt_above = 0;
rtt_reset(sk);
}
/* Measure RTT for each ack. */
static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked, s32 rtt)
{
struct illinois *ca = inet_csk_ca(sk);
ca->acked = pkts_acked;
/* dup ack, no rtt sample */
if (rtt < 0)
return;
/* ignore bogus values, this prevents wraparound in alpha math */
if (rtt > RTT_MAX)
rtt = RTT_MAX;
/* keep track of minimum RTT seen so far */
if (ca->base_rtt > rtt)
ca->base_rtt = rtt;
/* and max */
if (ca->max_rtt < rtt)
ca->max_rtt = rtt;
++ca->cnt_rtt;
ca->sum_rtt += rtt;
}
/* Maximum queuing delay */
static inline u32 max_delay(const struct illinois *ca)
{
return ca->max_rtt - ca->base_rtt;
}
/* Average queuing delay */
static inline u32 avg_delay(const struct illinois *ca)
{
u64 t = ca->sum_rtt;
do_div(t, ca->cnt_rtt);
return t - ca->base_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 (0.3)
*
* The result is a convex window growth curve.
*/
static u32 alpha(struct illinois *ca, u32 da, u32 dm)
{
u32 d1 = dm / 100; /* Low threshold */
if (da <= d1) {
/* If never got out of low delay zone, then use max */
if (!ca->rtt_above)
return ALPHA_MAX;
/* Wait for 5 good RTT's before allowing alpha to go alpha max.
* This prevents one good RTT from causing sudden window increase.
*/
if (++ca->rtt_low < theta)
return ca->alpha;
ca->rtt_low = 0;
ca->rtt_above = 0;
return ALPHA_MAX;
}
ca->rtt_above = 1;
/*
* Based on:
*
* (dm - d1) amin amax
* k1 = -------------------
* amax - amin
*
* (dm - d1) amin
* k2 = ---------------- - d1
* amax - amin
*
* k1
* alpha = ----------
* k2 + da
*/
dm -= d1;
da -= d1;
return (dm * ALPHA_MAX) /
(dm + (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
}
/*
* 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 u32 beta(u32 da, u32 dm)
{
u32 d2, d3;
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);
}
/* Update alpha and beta values once per RTT */
static void update_params(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
if (tp->snd_cwnd < win_thresh) {
ca->alpha = ALPHA_BASE;
ca->beta = BETA_BASE;
} else if (ca->cnt_rtt > 0) {
u32 dm = max_delay(ca);
u32 da = avg_delay(ca);
ca->alpha = alpha(ca, da, dm);
ca->beta = beta(da, dm);
}
rtt_reset(sk);
}
/*
* In case of loss, reset to default values
*/
static void tcp_illinois_state(struct sock *sk, u8 new_state)
{
struct illinois *ca = inet_csk_ca(sk);
if (new_state == TCP_CA_Loss) {
ca->alpha = ALPHA_BASE;
ca->beta = BETA_BASE;
ca->rtt_low = 0;
ca->rtt_above = 0;
rtt_reset(sk);
}
}
/*
* Increase window in response to successful acknowledgment.
*/
static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
if (after(ack, ca->end_seq))
update_params(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 {
u32 delta;
/* snd_cwnd_cnt is # of packets since last cwnd increment */
tp->snd_cwnd_cnt += ca->acked;
ca->acked = 1;
/* This is close approximation of:
* tp->snd_cwnd += alpha/tp->snd_cwnd
*/
delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT;
if (delta >= tp->snd_cwnd) {
tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
(u32) tp->snd_cwnd_clamp);
tp->snd_cwnd_cnt = 0;
}
}
}
static u32 tcp_illinois_ssthresh(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct illinois *ca = inet_csk_ca(sk);
/* Multiplicative decrease */
return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
}
/* Extract info for Tcp socket info provided via netlink. */
static void tcp_illinois_info(struct sock *sk, u32 ext,
struct sk_buff *skb)
{
const struct illinois *ca = inet_csk_ca(sk);
if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
struct tcpvegas_info info = {
.tcpv_enabled = 1,
.tcpv_rttcnt = ca->cnt_rtt,
.tcpv_minrtt = ca->base_rtt,
};
u64 t = ca->sum_rtt;
do_div(t, ca->cnt_rtt);
info.tcpv_rtt = t;
nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
}
}
static struct tcp_congestion_ops tcp_illinois = {
.flags = TCP_CONG_RTT_STAMP,
.init = tcp_illinois_init,
.ssthresh = tcp_illinois_ssthresh,
.min_cwnd = tcp_reno_min_cwnd,
.cong_avoid = tcp_illinois_cong_avoid,
.set_state = tcp_illinois_state,
.get_info = tcp_illinois_info,
.pkts_acked = tcp_illinois_acked,
.owner = THIS_MODULE,
.name = "illinois",
};
static int __init tcp_illinois_register(void)
{
BUILD_BUG_ON(sizeof(struct 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("1.0");