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229 lines
6.0 KiB
229 lines
6.0 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Binary Increase Congestion control for TCP |
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* Home page: |
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* http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC |
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* This is from the implementation of BICTCP in |
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* Lison-Xu, Kahaled Harfoush, and Injong Rhee. |
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* "Binary Increase Congestion Control for Fast, Long Distance |
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* Networks" in InfoComm 2004 |
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* Available from: |
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* http://netsrv.csc.ncsu.edu/export/bitcp.pdf |
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* |
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* Unless BIC is enabled and congestion window is large |
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* this behaves the same as the original Reno. |
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*/ |
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#include <linux/mm.h> |
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#include <linux/module.h> |
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#include <net/tcp.h> |
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#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation |
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* max_cwnd = snd_cwnd * beta |
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*/ |
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#define BICTCP_B 4 /* |
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* In binary search, |
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* go to point (max+min)/N |
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*/ |
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static int fast_convergence = 1; |
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static int max_increment = 16; |
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static int low_window = 14; |
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static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ |
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static int initial_ssthresh; |
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static int smooth_part = 20; |
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module_param(fast_convergence, int, 0644); |
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MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); |
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module_param(max_increment, int, 0644); |
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MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); |
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module_param(low_window, int, 0644); |
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MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)"); |
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module_param(beta, int, 0644); |
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MODULE_PARM_DESC(beta, "beta for multiplicative increase"); |
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module_param(initial_ssthresh, int, 0644); |
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MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); |
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module_param(smooth_part, int, 0644); |
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MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax"); |
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/* BIC TCP Parameters */ |
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struct bictcp { |
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u32 cnt; /* increase cwnd by 1 after ACKs */ |
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u32 last_max_cwnd; /* last maximum snd_cwnd */ |
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u32 last_cwnd; /* the last snd_cwnd */ |
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u32 last_time; /* time when updated last_cwnd */ |
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u32 epoch_start; /* beginning of an epoch */ |
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#define ACK_RATIO_SHIFT 4 |
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u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ |
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}; |
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static inline void bictcp_reset(struct bictcp *ca) |
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{ |
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ca->cnt = 0; |
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ca->last_max_cwnd = 0; |
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ca->last_cwnd = 0; |
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ca->last_time = 0; |
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ca->epoch_start = 0; |
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ca->delayed_ack = 2 << ACK_RATIO_SHIFT; |
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} |
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static void bictcp_init(struct sock *sk) |
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{ |
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struct bictcp *ca = inet_csk_ca(sk); |
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bictcp_reset(ca); |
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if (initial_ssthresh) |
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tcp_sk(sk)->snd_ssthresh = initial_ssthresh; |
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} |
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/* |
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* Compute congestion window to use. |
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*/ |
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static inline void bictcp_update(struct bictcp *ca, u32 cwnd) |
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{ |
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if (ca->last_cwnd == cwnd && |
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(s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32) |
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return; |
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ca->last_cwnd = cwnd; |
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ca->last_time = tcp_jiffies32; |
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if (ca->epoch_start == 0) /* record the beginning of an epoch */ |
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ca->epoch_start = tcp_jiffies32; |
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/* start off normal */ |
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if (cwnd <= low_window) { |
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ca->cnt = cwnd; |
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return; |
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} |
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/* binary increase */ |
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if (cwnd < ca->last_max_cwnd) { |
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__u32 dist = (ca->last_max_cwnd - cwnd) |
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/ BICTCP_B; |
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if (dist > max_increment) |
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/* linear increase */ |
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ca->cnt = cwnd / max_increment; |
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else if (dist <= 1U) |
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/* binary search increase */ |
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ca->cnt = (cwnd * smooth_part) / BICTCP_B; |
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else |
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/* binary search increase */ |
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ca->cnt = cwnd / dist; |
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} else { |
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/* slow start AMD linear increase */ |
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if (cwnd < ca->last_max_cwnd + BICTCP_B) |
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/* slow start */ |
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ca->cnt = (cwnd * smooth_part) / BICTCP_B; |
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else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1)) |
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/* slow start */ |
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ca->cnt = (cwnd * (BICTCP_B-1)) |
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/ (cwnd - ca->last_max_cwnd); |
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else |
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/* linear increase */ |
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ca->cnt = cwnd / max_increment; |
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} |
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/* if in slow start or link utilization is very low */ |
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if (ca->last_max_cwnd == 0) { |
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if (ca->cnt > 20) /* increase cwnd 5% per RTT */ |
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ca->cnt = 20; |
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} |
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ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; |
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if (ca->cnt == 0) /* cannot be zero */ |
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ca->cnt = 1; |
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} |
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static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct bictcp *ca = inet_csk_ca(sk); |
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if (!tcp_is_cwnd_limited(sk)) |
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return; |
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if (tcp_in_slow_start(tp)) { |
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acked = tcp_slow_start(tp, acked); |
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if (!acked) |
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return; |
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} |
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bictcp_update(ca, tp->snd_cwnd); |
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tcp_cong_avoid_ai(tp, ca->cnt, acked); |
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} |
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/* |
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* behave like Reno until low_window is reached, |
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* then increase congestion window slowly |
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*/ |
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static u32 bictcp_recalc_ssthresh(struct sock *sk) |
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{ |
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const struct tcp_sock *tp = tcp_sk(sk); |
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struct bictcp *ca = inet_csk_ca(sk); |
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ca->epoch_start = 0; /* end of epoch */ |
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/* Wmax and fast convergence */ |
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if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) |
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ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) |
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/ (2 * BICTCP_BETA_SCALE); |
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else |
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ca->last_max_cwnd = tp->snd_cwnd; |
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if (tp->snd_cwnd <= low_window) |
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return max(tp->snd_cwnd >> 1U, 2U); |
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else |
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return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); |
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} |
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static void bictcp_state(struct sock *sk, u8 new_state) |
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{ |
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if (new_state == TCP_CA_Loss) |
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bictcp_reset(inet_csk_ca(sk)); |
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} |
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/* Track delayed acknowledgment ratio using sliding window |
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* ratio = (15*ratio + sample) / 16 |
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*/ |
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static void bictcp_acked(struct sock *sk, const struct ack_sample *sample) |
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{ |
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const struct inet_connection_sock *icsk = inet_csk(sk); |
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if (icsk->icsk_ca_state == TCP_CA_Open) { |
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struct bictcp *ca = inet_csk_ca(sk); |
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ca->delayed_ack += sample->pkts_acked - |
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(ca->delayed_ack >> ACK_RATIO_SHIFT); |
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} |
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} |
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static struct tcp_congestion_ops bictcp __read_mostly = { |
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.init = bictcp_init, |
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.ssthresh = bictcp_recalc_ssthresh, |
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.cong_avoid = bictcp_cong_avoid, |
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.set_state = bictcp_state, |
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.undo_cwnd = tcp_reno_undo_cwnd, |
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.pkts_acked = bictcp_acked, |
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.owner = THIS_MODULE, |
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.name = "bic", |
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}; |
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static int __init bictcp_register(void) |
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{ |
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BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); |
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return tcp_register_congestion_control(&bictcp); |
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} |
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static void __exit bictcp_unregister(void) |
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{ |
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tcp_unregister_congestion_control(&bictcp); |
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} |
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module_init(bictcp_register); |
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module_exit(bictcp_unregister); |
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MODULE_AUTHOR("Stephen Hemminger"); |
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MODULE_LICENSE("GPL"); |
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MODULE_DESCRIPTION("BIC TCP");
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