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332 lines
8.8 KiB
C
332 lines
8.8 KiB
C
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/*
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* Binary Increase Congestion control for TCP
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*
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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://www.csc.ncsu.edu/faculty/rhee/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/config.h>
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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 = 32;
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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 low_utilization_threshold = 153;
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static int low_utilization_period = 2;
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static int initial_ssthresh = 100;
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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(low_utilization_threshold, int, 0644);
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MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode");
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module_param(low_utilization_period, int, 0644);
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MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)");
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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 loss_cwnd; /* congestion window at last loss */
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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 delay_min; /* min delay */
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u32 delay_max; /* max delay */
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u32 last_delay;
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u8 low_utilization;/* 0: high; 1: low */
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u32 low_utilization_start; /* starting time of low utilization detection*/
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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->loss_cwnd = 0;
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ca->last_cwnd = 0;
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ca->last_time = 0;
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ca->delay_min = 0;
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ca->delay_max = 0;
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ca->last_delay = 0;
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ca->low_utilization = 0;
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ca->low_utilization_start = 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 tcp_sock *tp)
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{
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bictcp_reset(tcp_ca(tp));
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if (initial_ssthresh)
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tp->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_time_stamp - 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_time_stamp;
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if (ca->epoch_start == 0) /* record the beginning of an epoch */
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ca->epoch_start = tcp_time_stamp;
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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->loss_cwnd == 0 ||
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(cwnd > ca->loss_cwnd && ca->low_utilization)) {
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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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/* Detect low utilization in congestion avoidance */
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static inline void bictcp_low_utilization(struct tcp_sock *tp, int flag)
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{
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struct bictcp *ca = tcp_ca(tp);
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u32 dist, delay;
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/* No time stamp */
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if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
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/* Discard delay samples right after fast recovery */
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tcp_time_stamp < ca->epoch_start + HZ ||
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/* this delay samples may not be accurate */
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flag == 0) {
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ca->last_delay = 0;
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goto notlow;
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}
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delay = ca->last_delay<<3; /* use the same scale as tp->srtt*/
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ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
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if (delay == 0) /* no previous delay sample */
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goto notlow;
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/* first time call or link delay decreases */
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if (ca->delay_min == 0 || ca->delay_min > delay) {
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ca->delay_min = ca->delay_max = delay;
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goto notlow;
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}
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if (ca->delay_max < delay)
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ca->delay_max = delay;
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/* utilization is low, if avg delay < dist*threshold
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for checking_period time */
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dist = ca->delay_max - ca->delay_min;
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if (dist <= ca->delay_min>>6 ||
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tp->srtt - ca->delay_min >= (dist*low_utilization_threshold)>>10)
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goto notlow;
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if (ca->low_utilization_start == 0) {
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ca->low_utilization = 0;
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ca->low_utilization_start = tcp_time_stamp;
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} else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
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> low_utilization_period*HZ) {
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ca->low_utilization = 1;
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}
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return;
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notlow:
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ca->low_utilization = 0;
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ca->low_utilization_start = 0;
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}
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static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack,
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u32 seq_rtt, u32 in_flight, int data_acked)
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{
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struct bictcp *ca = tcp_ca(tp);
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bictcp_low_utilization(tp, data_acked);
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if (in_flight < tp->snd_cwnd)
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return;
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if (tp->snd_cwnd <= tp->snd_ssthresh) {
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/* In "safe" area, increase. */
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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} else {
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bictcp_update(ca, tp->snd_cwnd);
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/* In dangerous area, increase slowly.
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* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
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*/
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if (tp->snd_cwnd_cnt >= ca->cnt) {
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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tp->snd_cwnd_cnt = 0;
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} else
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tp->snd_cwnd_cnt++;
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}
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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 tcp_sock *tp)
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{
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struct bictcp *ca = tcp_ca(tp);
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ca->epoch_start = 0; /* end of epoch */
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/* in case of wrong delay_max*/
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if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
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ca->delay_max = ca->delay_min
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+ ((ca->delay_max - ca->delay_min)* 90) / 100;
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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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ca->loss_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 u32 bictcp_undo_cwnd(struct tcp_sock *tp)
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{
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struct bictcp *ca = tcp_ca(tp);
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return max(tp->snd_cwnd, ca->last_max_cwnd);
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}
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static u32 bictcp_min_cwnd(struct tcp_sock *tp)
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{
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return tp->snd_ssthresh;
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}
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static void bictcp_state(struct tcp_sock *tp, u8 new_state)
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{
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if (new_state == TCP_CA_Loss)
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bictcp_reset(tcp_ca(tp));
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}
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/* Track delayed acknowledgement 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 tcp_sock *tp, u32 cnt)
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{
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if (cnt > 0 && tp->ca_state == TCP_CA_Open) {
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struct bictcp *ca = tcp_ca(tp);
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cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
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ca->delayed_ack += cnt;
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}
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}
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static struct tcp_congestion_ops bictcp = {
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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 = bictcp_undo_cwnd,
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.min_cwnd = bictcp_min_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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BUG_ON(sizeof(struct bictcp) > TCP_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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