![Arnaldo Carvalho de Melo](/assets/img/avatar_default.png)
This changeset basically moves tcp_sk()->{ca_ops,ca_state,etc} to inet_csk(), minimal renaming/moving done in this changeset to ease review. Most of it is just changes of struct tcp_sock * to struct sock * parameters. With this we move to a state closer to two interesting goals: 1. Generalisation of net/ipv4/tcp_diag.c, becoming inet_diag.c, being used for any INET transport protocol that has struct inet_hashinfo and are derived from struct inet_connection_sock. Keeps the userspace API, that will just not display DCCP sockets, while newer versions of tools can support DCCP. 2. INET generic transport pluggable Congestion Avoidance infrastructure, using the current TCP CA infrastructure with DCCP. Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com> Signed-off-by: David S. Miller <davem@davemloft.net>
338 lines
9 KiB
C
338 lines
9 KiB
C
/*
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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 sock *sk)
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{
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bictcp_reset(inet_csk_ca(sk));
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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_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 sock *sk, int flag)
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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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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 sock *sk, u32 ack,
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u32 seq_rtt, u32 in_flight, int data_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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bictcp_low_utilization(sk, 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 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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/* 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 sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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const struct bictcp *ca = inet_csk_ca(sk);
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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 sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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return tp->snd_ssthresh;
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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 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 sock *sk, u32 cnt)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
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struct bictcp *ca = inet_csk_ca(sk);
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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) > 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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