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- /*
- * 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://tamerbasar.csl.illinois.edu/LiuBasarSrikantPerfEvalArtJun2008.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 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, const struct ack_sample *sample)
- {
- struct illinois *ca = inet_csk_ca(sk);
- s32 rtt_us = sample->rtt_us;
- ca->acked = sample->pkts_acked;
- /* dup ack, no rtt sample */
- if (rtt_us < 0)
- return;
- /* ignore bogus values, this prevents wraparound in alpha math */
- if (rtt_us > RTT_MAX)
- rtt_us = RTT_MAX;
- /* keep track of minimum RTT seen so far */
- if (ca->base_rtt > rtt_us)
- ca->base_rtt = rtt_us;
- /* and max */
- if (ca->max_rtt < rtt_us)
- ca->max_rtt = rtt_us;
- ++ca->cnt_rtt;
- ca->sum_rtt += rtt_us;
- }
- /* 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 acked)
- {
- 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))
- return;
- /* In slow start */
- if (tcp_in_slow_start(tp))
- tcp_slow_start(tp, acked);
- 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 size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
- union tcp_cc_info *info)
- {
- const struct illinois *ca = inet_csk_ca(sk);
- if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
- info->vegas.tcpv_enabled = 1;
- info->vegas.tcpv_rttcnt = ca->cnt_rtt;
- info->vegas.tcpv_minrtt = ca->base_rtt;
- info->vegas.tcpv_rtt = 0;
- if (info->vegas.tcpv_rttcnt > 0) {
- u64 t = ca->sum_rtt;
- do_div(t, info->vegas.tcpv_rttcnt);
- info->vegas.tcpv_rtt = t;
- }
- *attr = INET_DIAG_VEGASINFO;
- return sizeof(struct tcpvegas_info);
- }
- return 0;
- }
- static struct tcp_congestion_ops tcp_illinois __read_mostly = {
- .init = tcp_illinois_init,
- .ssthresh = tcp_illinois_ssthresh,
- .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");
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