532 строки
15 KiB
C
532 строки
15 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* TCP CUBIC: Binary Increase Congestion control for TCP v2.3
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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 CUBIC TCP in
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* Sangtae Ha, Injong Rhee and Lisong Xu,
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* "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
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* in ACM SIGOPS Operating System Review, July 2008.
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* Available from:
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* http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
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*
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* CUBIC integrates a new slow start algorithm, called HyStart.
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* The details of HyStart are presented in
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* Sangtae Ha and Injong Rhee,
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* "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
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* Available from:
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* http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
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*
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* All testing results are available from:
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* http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
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*
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* Unless CUBIC 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 <linux/math64.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_HZ 10 /* BIC HZ 2^10 = 1024 */
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/* Two methods of hybrid slow start */
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#define HYSTART_ACK_TRAIN 0x1
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#define HYSTART_DELAY 0x2
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/* Number of delay samples for detecting the increase of delay */
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#define HYSTART_MIN_SAMPLES 8
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#define HYSTART_DELAY_MIN (4000U) /* 4 ms */
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#define HYSTART_DELAY_MAX (16000U) /* 16 ms */
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#define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
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static int fast_convergence __read_mostly = 1;
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static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
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static int initial_ssthresh __read_mostly;
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static int bic_scale __read_mostly = 41;
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static int tcp_friendliness __read_mostly = 1;
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static int hystart __read_mostly = 1;
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static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
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static int hystart_low_window __read_mostly = 16;
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static int hystart_ack_delta_us __read_mostly = 2000;
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static u32 cube_rtt_scale __read_mostly;
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static u32 beta_scale __read_mostly;
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static u64 cube_factor __read_mostly;
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/* Note parameters that are used for precomputing scale factors are read-only */
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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(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(bic_scale, int, 0444);
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MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
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module_param(tcp_friendliness, int, 0644);
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MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
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module_param(hystart, int, 0644);
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MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
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module_param(hystart_detect, int, 0644);
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MODULE_PARM_DESC(hystart_detect, "hybrid slow start detection mechanisms"
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" 1: packet-train 2: delay 3: both packet-train and delay");
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module_param(hystart_low_window, int, 0644);
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MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
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module_param(hystart_ack_delta_us, int, 0644);
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MODULE_PARM_DESC(hystart_ack_delta_us, "spacing between ack's indicating train (usecs)");
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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 bic_origin_point;/* origin point of bic function */
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u32 bic_K; /* time to origin point
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from the beginning of the current epoch */
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u32 delay_min; /* min delay (usec) */
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u32 epoch_start; /* beginning of an epoch */
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u32 ack_cnt; /* number of acks */
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u32 tcp_cwnd; /* estimated tcp cwnd */
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u16 unused;
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u8 sample_cnt; /* number of samples to decide curr_rtt */
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u8 found; /* the exit point is found? */
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u32 round_start; /* beginning of each round */
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u32 end_seq; /* end_seq of the round */
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u32 last_ack; /* last time when the ACK spacing is close */
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u32 curr_rtt; /* the minimum rtt of current round */
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};
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static inline void bictcp_reset(struct bictcp *ca)
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{
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memset(ca, 0, offsetof(struct bictcp, unused));
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ca->found = 0;
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}
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static inline u32 bictcp_clock_us(const struct sock *sk)
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{
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return tcp_sk(sk)->tcp_mstamp;
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}
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static inline void bictcp_hystart_reset(struct sock *sk)
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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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ca->round_start = ca->last_ack = bictcp_clock_us(sk);
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ca->end_seq = tp->snd_nxt;
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ca->curr_rtt = ~0U;
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ca->sample_cnt = 0;
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}
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static void cubictcp_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 (hystart)
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bictcp_hystart_reset(sk);
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if (!hystart && initial_ssthresh)
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tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
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}
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static void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event)
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{
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if (event == CA_EVENT_TX_START) {
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struct bictcp *ca = inet_csk_ca(sk);
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u32 now = tcp_jiffies32;
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s32 delta;
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delta = now - tcp_sk(sk)->lsndtime;
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/* We were application limited (idle) for a while.
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* Shift epoch_start to keep cwnd growth to cubic curve.
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*/
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if (ca->epoch_start && delta > 0) {
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ca->epoch_start += delta;
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if (after(ca->epoch_start, now))
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ca->epoch_start = now;
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}
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return;
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}
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}
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/* calculate the cubic root of x using a table lookup followed by one
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* Newton-Raphson iteration.
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* Avg err ~= 0.195%
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*/
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static u32 cubic_root(u64 a)
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{
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u32 x, b, shift;
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/*
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* cbrt(x) MSB values for x MSB values in [0..63].
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* Precomputed then refined by hand - Willy Tarreau
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*
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* For x in [0..63],
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* v = cbrt(x << 18) - 1
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* cbrt(x) = (v[x] + 10) >> 6
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*/
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static const u8 v[] = {
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/* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
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/* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
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/* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
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/* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
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/* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
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/* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
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/* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
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/* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
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};
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b = fls64(a);
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if (b < 7) {
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/* a in [0..63] */
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return ((u32)v[(u32)a] + 35) >> 6;
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}
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b = ((b * 84) >> 8) - 1;
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shift = (a >> (b * 3));
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x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
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/*
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* Newton-Raphson iteration
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* 2
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* x = ( 2 * x + a / x ) / 3
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* k+1 k k
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*/
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x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
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x = ((x * 341) >> 10);
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return x;
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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, u32 acked)
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{
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u32 delta, bic_target, max_cnt;
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u64 offs, t;
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ca->ack_cnt += acked; /* count the number of ACKed packets */
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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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/* The CUBIC function can update ca->cnt at most once per jiffy.
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* On all cwnd reduction events, ca->epoch_start is set to 0,
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* which will force a recalculation of ca->cnt.
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*/
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if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
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goto tcp_friendliness;
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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) {
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ca->epoch_start = tcp_jiffies32; /* record beginning */
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ca->ack_cnt = acked; /* start counting */
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ca->tcp_cwnd = cwnd; /* syn with cubic */
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if (ca->last_max_cwnd <= cwnd) {
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ca->bic_K = 0;
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ca->bic_origin_point = cwnd;
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} else {
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/* Compute new K based on
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* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
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*/
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ca->bic_K = cubic_root(cube_factor
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* (ca->last_max_cwnd - cwnd));
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ca->bic_origin_point = ca->last_max_cwnd;
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}
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}
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/* cubic function - calc*/
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/* calculate c * time^3 / rtt,
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* while considering overflow in calculation of time^3
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* (so time^3 is done by using 64 bit)
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* and without the support of division of 64bit numbers
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* (so all divisions are done by using 32 bit)
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* also NOTE the unit of those veriables
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* time = (t - K) / 2^bictcp_HZ
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* c = bic_scale >> 10
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* rtt = (srtt >> 3) / HZ
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* !!! The following code does not have overflow problems,
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* if the cwnd < 1 million packets !!!
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*/
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t = (s32)(tcp_jiffies32 - ca->epoch_start);
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t += usecs_to_jiffies(ca->delay_min);
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/* change the unit from HZ to bictcp_HZ */
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t <<= BICTCP_HZ;
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do_div(t, HZ);
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if (t < ca->bic_K) /* t - K */
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offs = ca->bic_K - t;
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else
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offs = t - ca->bic_K;
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/* c/rtt * (t-K)^3 */
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delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
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if (t < ca->bic_K) /* below origin*/
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bic_target = ca->bic_origin_point - delta;
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else /* above origin*/
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bic_target = ca->bic_origin_point + delta;
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/* cubic function - calc bictcp_cnt*/
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if (bic_target > cwnd) {
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ca->cnt = cwnd / (bic_target - cwnd);
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} else {
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ca->cnt = 100 * cwnd; /* very small increment*/
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}
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/*
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* The initial growth of cubic function may be too conservative
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* when the available bandwidth is still unknown.
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*/
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if (ca->last_max_cwnd == 0 && ca->cnt > 20)
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ca->cnt = 20; /* increase cwnd 5% per RTT */
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tcp_friendliness:
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/* TCP Friendly */
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if (tcp_friendliness) {
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u32 scale = beta_scale;
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delta = (cwnd * scale) >> 3;
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while (ca->ack_cnt > delta) { /* update tcp cwnd */
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ca->ack_cnt -= delta;
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ca->tcp_cwnd++;
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}
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if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
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delta = ca->tcp_cwnd - cwnd;
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max_cnt = cwnd / delta;
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if (ca->cnt > max_cnt)
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ca->cnt = max_cnt;
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}
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}
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/* The maximum rate of cwnd increase CUBIC allows is 1 packet per
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* 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
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*/
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ca->cnt = max(ca->cnt, 2U);
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}
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static void cubictcp_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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if (hystart && after(ack, ca->end_seq))
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bictcp_hystart_reset(sk);
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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, acked);
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tcp_cong_avoid_ai(tp, ca->cnt, acked);
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}
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static u32 cubictcp_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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return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
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}
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static void cubictcp_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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bictcp_hystart_reset(sk);
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}
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}
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/* Account for TSO/GRO delays.
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* Otherwise short RTT flows could get too small ssthresh, since during
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* slow start we begin with small TSO packets and ca->delay_min would
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* not account for long aggregation delay when TSO packets get bigger.
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* Ideally even with a very small RTT we would like to have at least one
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* TSO packet being sent and received by GRO, and another one in qdisc layer.
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* We apply another 100% factor because @rate is doubled at this point.
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* We cap the cushion to 1ms.
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*/
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static u32 hystart_ack_delay(struct sock *sk)
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{
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unsigned long rate;
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rate = READ_ONCE(sk->sk_pacing_rate);
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if (!rate)
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return 0;
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return min_t(u64, USEC_PER_MSEC,
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div64_ul((u64)GSO_MAX_SIZE * 4 * USEC_PER_SEC, rate));
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}
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static void hystart_update(struct sock *sk, u32 delay)
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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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u32 threshold;
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if (hystart_detect & HYSTART_ACK_TRAIN) {
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u32 now = bictcp_clock_us(sk);
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/* first detection parameter - ack-train detection */
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if ((s32)(now - ca->last_ack) <= hystart_ack_delta_us) {
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ca->last_ack = now;
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threshold = ca->delay_min + hystart_ack_delay(sk);
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/* Hystart ack train triggers if we get ack past
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* ca->delay_min/2.
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* Pacing might have delayed packets up to RTT/2
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* during slow start.
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*/
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if (sk->sk_pacing_status == SK_PACING_NONE)
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threshold >>= 1;
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if ((s32)(now - ca->round_start) > threshold) {
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ca->found = 1;
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pr_debug("hystart_ack_train (%u > %u) delay_min %u (+ ack_delay %u) cwnd %u\n",
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now - ca->round_start, threshold,
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ca->delay_min, hystart_ack_delay(sk), tp->snd_cwnd);
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NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTTRAINDETECT);
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NET_ADD_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTTRAINCWND,
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tp->snd_cwnd);
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tp->snd_ssthresh = tp->snd_cwnd;
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}
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}
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}
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if (hystart_detect & HYSTART_DELAY) {
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/* obtain the minimum delay of more than sampling packets */
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if (ca->curr_rtt > delay)
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ca->curr_rtt = delay;
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if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
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ca->sample_cnt++;
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} else {
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if (ca->curr_rtt > ca->delay_min +
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HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
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ca->found = 1;
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NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTDELAYDETECT);
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NET_ADD_STATS(sock_net(sk),
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LINUX_MIB_TCPHYSTARTDELAYCWND,
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tp->snd_cwnd);
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tp->snd_ssthresh = tp->snd_cwnd;
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}
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}
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}
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}
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static void cubictcp_acked(struct sock *sk, const struct ack_sample *sample)
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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 delay;
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/* Some calls are for duplicates without timetamps */
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if (sample->rtt_us < 0)
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return;
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/* Discard delay samples right after fast recovery */
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if (ca->epoch_start && (s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
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return;
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|
|
|
delay = sample->rtt_us;
|
|
if (delay == 0)
|
|
delay = 1;
|
|
|
|
/* first time call or link delay decreases */
|
|
if (ca->delay_min == 0 || ca->delay_min > delay)
|
|
ca->delay_min = delay;
|
|
|
|
/* hystart triggers when cwnd is larger than some threshold */
|
|
if (!ca->found && tcp_in_slow_start(tp) && hystart &&
|
|
tp->snd_cwnd >= hystart_low_window)
|
|
hystart_update(sk, delay);
|
|
}
|
|
|
|
static struct tcp_congestion_ops cubictcp __read_mostly = {
|
|
.init = cubictcp_init,
|
|
.ssthresh = cubictcp_recalc_ssthresh,
|
|
.cong_avoid = cubictcp_cong_avoid,
|
|
.set_state = cubictcp_state,
|
|
.undo_cwnd = tcp_reno_undo_cwnd,
|
|
.cwnd_event = cubictcp_cwnd_event,
|
|
.pkts_acked = cubictcp_acked,
|
|
.owner = THIS_MODULE,
|
|
.name = "cubic",
|
|
};
|
|
|
|
static int __init cubictcp_register(void)
|
|
{
|
|
BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
|
|
|
|
/* Precompute a bunch of the scaling factors that are used per-packet
|
|
* based on SRTT of 100ms
|
|
*/
|
|
|
|
beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
|
|
/ (BICTCP_BETA_SCALE - beta);
|
|
|
|
cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
|
|
|
|
/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
|
|
* so K = cubic_root( (wmax-cwnd)*rtt/c )
|
|
* the unit of K is bictcp_HZ=2^10, not HZ
|
|
*
|
|
* c = bic_scale >> 10
|
|
* rtt = 100ms
|
|
*
|
|
* the following code has been designed and tested for
|
|
* cwnd < 1 million packets
|
|
* RTT < 100 seconds
|
|
* HZ < 1,000,00 (corresponding to 10 nano-second)
|
|
*/
|
|
|
|
/* 1/c * 2^2*bictcp_HZ * srtt */
|
|
cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
|
|
|
|
/* divide by bic_scale and by constant Srtt (100ms) */
|
|
do_div(cube_factor, bic_scale * 10);
|
|
|
|
return tcp_register_congestion_control(&cubictcp);
|
|
}
|
|
|
|
static void __exit cubictcp_unregister(void)
|
|
{
|
|
tcp_unregister_congestion_control(&cubictcp);
|
|
}
|
|
|
|
module_init(cubictcp_register);
|
|
module_exit(cubictcp_unregister);
|
|
|
|
MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_DESCRIPTION("CUBIC TCP");
|
|
MODULE_VERSION("2.3");
|