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Release 4.11 net/ipv4/tcp_cubic.c

Directory: net/ipv4
/*
 * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
 * Home page:
 *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
 * This is from the implementation of CUBIC TCP in
 * Sangtae Ha, Injong Rhee and Lisong Xu,
 *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
 *  in ACM SIGOPS Operating System Review, July 2008.
 * Available from:
 *  http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
 *
 * CUBIC integrates a new slow start algorithm, called HyStart.
 * The details of HyStart are presented in
 *  Sangtae Ha and Injong Rhee,
 *  "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
 * Available from:
 *  http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
 *
 * All testing results are available from:
 * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
 *
 * Unless CUBIC is enabled and congestion window is large
 * this behaves the same as the original Reno.
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/math64.h>
#include <net/tcp.h>


#define BICTCP_BETA_SCALE    1024	
/* Scale factor beta calculation
                                         * max_cwnd = snd_cwnd * beta
                                         */

#define	BICTCP_HZ		10	
/* BIC HZ 2^10 = 1024 */

/* Two methods of hybrid slow start */

#define HYSTART_ACK_TRAIN	0x1

#define HYSTART_DELAY		0x2

/* Number of delay samples for detecting the increase of delay */

#define HYSTART_MIN_SAMPLES	8

#define HYSTART_DELAY_MIN	(4U<<3)

#define HYSTART_DELAY_MAX	(16U<<3)

#define HYSTART_DELAY_THRESH(x)	clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)


static int fast_convergence __read_mostly = 1;

static int beta __read_mostly = 717;	
/* = 717/1024 (BICTCP_BETA_SCALE) */

static int initial_ssthresh __read_mostly;

static int bic_scale __read_mostly = 41;

static int tcp_friendliness __read_mostly = 1;


static int hystart __read_mostly = 1;

static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;

static int hystart_low_window __read_mostly = 16;

static int hystart_ack_delta __read_mostly = 2;


static u32 cube_rtt_scale __read_mostly;

static u32 beta_scale __read_mostly;

static u64 cube_factor __read_mostly;

/* Note parameters that are used for precomputing scale factors are read-only */
module_param(fast_convergence, int, 0644);
MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
module_param(beta, int, 0644);
MODULE_PARM_DESC(beta, "beta for multiplicative increase");
module_param(initial_ssthresh, int, 0644);
MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
module_param(bic_scale, int, 0444);
MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
module_param(tcp_friendliness, int, 0644);
MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
module_param(hystart, int, 0644);
MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
module_param(hystart_detect, int, 0644);
MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms"
		 " 1: packet-train 2: delay 3: both packet-train and delay");
module_param(hystart_low_window, int, 0644);
MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
module_param(hystart_ack_delta, int, 0644);
MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)");

/* BIC TCP Parameters */

struct bictcp {
	
u32	cnt;		/* increase cwnd by 1 after ACKs */
	
u32	last_max_cwnd;	/* last maximum snd_cwnd */
	
u32	loss_cwnd;	/* congestion window at last loss */
	
u32	last_cwnd;	/* the last snd_cwnd */
	
u32	last_time;	/* time when updated last_cwnd */
	
u32	bic_origin_point;/* origin point of bic function */
	
u32	bic_K;		/* time to origin point
                                   from the beginning of the current epoch */
	
u32	delay_min;	/* min delay (msec << 3) */
	
u32	epoch_start;	/* beginning of an epoch */
	
u32	ack_cnt;	/* number of acks */
	
u32	tcp_cwnd;	/* estimated tcp cwnd */
	
u16	unused;
	
u8	sample_cnt;	/* number of samples to decide curr_rtt */
	
u8	found;		/* the exit point is found? */
	
u32	round_start;	/* beginning of each round */
	
u32	end_seq;	/* end_seq of the round */
	
u32	last_ack;	/* last time when the ACK spacing is close */
	
u32	curr_rtt;	/* the minimum rtt of current round */
};


static inline void bictcp_reset(struct bictcp *ca) { ca->cnt = 0; ca->last_max_cwnd = 0; ca->last_cwnd = 0; ca->last_time = 0; ca->bic_origin_point = 0; ca->bic_K = 0; ca->delay_min = 0; ca->epoch_start = 0; ca->ack_cnt = 0; ca->tcp_cwnd = 0; ca->found = 0; }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger7191.03%150.00%
Sangtae Ha78.97%150.00%
Total78100.00%2100.00%


static inline u32 bictcp_clock(void) { #if HZ < 1000 return ktime_to_ms(ktime_get_real()); #else return jiffies_to_msecs(jiffies); #endif }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger31100.00%1100.00%
Total31100.00%1100.00%


static inline void bictcp_hystart_reset(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct bictcp *ca = inet_csk_ca(sk); ca->round_start = ca->last_ack = bictcp_clock(); ca->end_seq = tp->snd_nxt; ca->curr_rtt = 0; ca->sample_cnt = 0; }

Contributors

PersonTokensPropCommitsCommitProp
Sangtae Ha5993.65%133.33%
Stephen Hemminger46.35%266.67%
Total63100.00%3100.00%


static void bictcp_init(struct sock *sk) { struct bictcp *ca = inet_csk_ca(sk); bictcp_reset(ca); ca->loss_cwnd = 0; if (hystart) bictcp_hystart_reset(sk); if (!hystart && initial_ssthresh) tcp_sk(sk)->snd_ssthresh = initial_ssthresh; }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger3052.63%133.33%
Neal Cardwell1526.32%133.33%
Sangtae Ha1221.05%133.33%
Total57100.00%3100.00%


static void bictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) { if (event == CA_EVENT_TX_START) { struct bictcp *ca = inet_csk_ca(sk); u32 now = tcp_time_stamp; s32 delta; delta = now - tcp_sk(sk)->lsndtime; /* We were application limited (idle) for a while. * Shift epoch_start to keep cwnd growth to cubic curve. */ if (ca->epoch_start && delta > 0) { ca->epoch_start += delta; if (after(ca->epoch_start, now)) ca->epoch_start = now; } return; } }

Contributors

PersonTokensPropCommitsCommitProp
Eric Dumazet89100.00%2100.00%
Total89100.00%2100.00%

/* calculate the cubic root of x using a table lookup followed by one * Newton-Raphson iteration. * Avg err ~= 0.195% */
static u32 cubic_root(u64 a) { u32 x, b, shift; /* * cbrt(x) MSB values for x MSB values in [0..63]. * Precomputed then refined by hand - Willy Tarreau * * For x in [0..63], * v = cbrt(x << 18) - 1 * cbrt(x) = (v[x] + 10) >> 6 */ static const u8 v[] = { /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118, /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156, /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179, /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199, /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215, /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229, /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242, /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254, }; b = fls64(a); if (b < 7) { /* a in [0..63] */ return ((u32)v[(u32)a] + 35) >> 6; } b = ((b * 84) >> 8) - 1; shift = (a >> (b * 3)); x = ((u32)(((u32)v[shift] + 10) << b)) >> 6; /* * Newton-Raphson iteration * 2 * x = ( 2 * x + a / x ) / 3 * k+1 k k */ x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1))); x = ((x * 341) >> 10); return x; }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger29199.66%480.00%
Roman Zippel10.34%120.00%
Total292100.00%5100.00%

/* * Compute congestion window to use. */
static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked) { u32 delta, bic_target, max_cnt; u64 offs, t; ca->ack_cnt += acked; /* count the number of ACKed packets */ if (ca->last_cwnd == cwnd && (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) return; /* The CUBIC function can update ca->cnt at most once per jiffy. * On all cwnd reduction events, ca->epoch_start is set to 0, * which will force a recalculation of ca->cnt. */ if (ca->epoch_start && tcp_time_stamp == ca->last_time) goto tcp_friendliness; ca->last_cwnd = cwnd; ca->last_time = tcp_time_stamp; if (ca->epoch_start == 0) { ca->epoch_start = tcp_time_stamp; /* record beginning */ ca->ack_cnt = acked; /* start counting */ ca->tcp_cwnd = cwnd; /* syn with cubic */ if (ca->last_max_cwnd <= cwnd) { ca->bic_K = 0; ca->bic_origin_point = cwnd; } else { /* Compute new K based on * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) */ ca->bic_K = cubic_root(cube_factor * (ca->last_max_cwnd - cwnd)); ca->bic_origin_point = ca->last_max_cwnd; } } /* cubic function - calc*/ /* calculate c * time^3 / rtt, * while considering overflow in calculation of time^3 * (so time^3 is done by using 64 bit) * and without the support of division of 64bit numbers * (so all divisions are done by using 32 bit) * also NOTE the unit of those veriables * time = (t - K) / 2^bictcp_HZ * c = bic_scale >> 10 * rtt = (srtt >> 3) / HZ * !!! The following code does not have overflow problems, * if the cwnd < 1 million packets !!! */ t = (s32)(tcp_time_stamp - ca->epoch_start); t += msecs_to_jiffies(ca->delay_min >> 3); /* change the unit from HZ to bictcp_HZ */ t <<= BICTCP_HZ; do_div(t, HZ); if (t < ca->bic_K) /* t - K */ offs = ca->bic_K - t; else offs = t - ca->bic_K; /* c/rtt * (t-K)^3 */ delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); if (t < ca->bic_K) /* below origin*/ bic_target = ca->bic_origin_point - delta; else /* above origin*/ bic_target = ca->bic_origin_point + delta; /* cubic function - calc bictcp_cnt*/ if (bic_target > cwnd) { ca->cnt = cwnd / (bic_target - cwnd); } else { ca->cnt = 100 * cwnd; /* very small increment*/ } /* * The initial growth of cubic function may be too conservative * when the available bandwidth is still unknown. */ if (ca->last_max_cwnd == 0 && ca->cnt > 20) ca->cnt = 20; /* increase cwnd 5% per RTT */ tcp_friendliness: /* TCP Friendly */ if (tcp_friendliness) { u32 scale = beta_scale; delta = (cwnd * scale) >> 3; while (ca->ack_cnt > delta) { /* update tcp cwnd */ ca->ack_cnt -= delta; ca->tcp_cwnd++; } if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */ delta = ca->tcp_cwnd - cwnd; max_cnt = cwnd / delta; if (ca->cnt > max_cnt) ca->cnt = max_cnt; } } /* The maximum rate of cwnd increase CUBIC allows is 1 packet per * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT. */ ca->cnt = max(ca->cnt, 2U); }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger35581.24%541.67%
Neal Cardwell337.55%433.33%
Eric Dumazet276.18%18.33%
Sangtae Ha214.81%18.33%
Hideaki Yoshifuji / 吉藤英明10.23%18.33%
Total437100.00%12100.00%


static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) { struct tcp_sock *tp = tcp_sk(sk); struct bictcp *ca = inet_csk_ca(sk); if (!tcp_is_cwnd_limited(sk)) return; if (tcp_in_slow_start(tp)) { if (hystart && after(ack, ca->end_seq)) bictcp_hystart_reset(sk); acked = tcp_slow_start(tp, acked); if (!acked) return; } bictcp_update(ca, tp->snd_cwnd, acked); tcp_cong_avoid_ai(tp, ca->cnt, acked); }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger6861.82%114.29%
Sangtae Ha2018.18%114.29%
Neal Cardwell1210.91%228.57%
Yuchung Cheng65.45%228.57%
Ilpo Järvinen43.64%114.29%
Total110100.00%7100.00%


static u32 bictcp_recalc_ssthresh(struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); struct bictcp *ca = inet_csk_ca(sk); ca->epoch_start = 0; /* end of epoch */ /* Wmax and fast convergence */ if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) / (2 * BICTCP_BETA_SCALE); else ca->last_max_cwnd = tp->snd_cwnd; ca->loss_cwnd = tp->snd_cwnd; return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger107100.00%1100.00%
Total107100.00%1100.00%


static u32 bictcp_undo_cwnd(struct sock *sk) { struct bictcp *ca = inet_csk_ca(sk); return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd); }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger3597.22%150.00%
Neal Cardwell12.78%150.00%
Total36100.00%2100.00%


static void bictcp_state(struct sock *sk, u8 new_state) { if (new_state == TCP_CA_Loss) { bictcp_reset(inet_csk_ca(sk)); bictcp_hystart_reset(sk); } }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger2777.14%150.00%
Sangtae Ha822.86%150.00%
Total35100.00%2100.00%


static void hystart_update(struct sock *sk, u32 delay) { struct tcp_sock *tp = tcp_sk(sk); struct bictcp *ca = inet_csk_ca(sk); if (ca->found & hystart_detect) return; if (hystart_detect & HYSTART_ACK_TRAIN) { u32 now = bictcp_clock(); /* first detection parameter - ack-train detection */ if ((s32)(now - ca->last_ack) <= hystart_ack_delta) { ca->last_ack = now; if ((s32)(now - ca->round_start) > ca->delay_min >> 4) { ca->found |= HYSTART_ACK_TRAIN; NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHYSTARTTRAINDETECT); NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPHYSTARTTRAINCWND, tp->snd_cwnd); tp->snd_ssthresh = tp->snd_cwnd; } } } if (hystart_detect & HYSTART_DELAY) { /* obtain the minimum delay of more than sampling packets */ if (ca->sample_cnt < HYSTART_MIN_SAMPLES) { if (ca->curr_rtt == 0 || ca->curr_rtt > delay) ca->curr_rtt = delay; ca->sample_cnt++; } else { if (ca->curr_rtt > ca->delay_min + HYSTART_DELAY_THRESH(ca->delay_min >> 3)) { ca->found |= HYSTART_DELAY; NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHYSTARTDELAYDETECT); NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPHYSTARTDELAYCWND, tp->snd_cwnd); tp->snd_ssthresh = tp->snd_cwnd; } } } }

Contributors

PersonTokensPropCommitsCommitProp
Sangtae Ha15060.98%112.50%
Eric Dumazet7630.89%337.50%
Stephen Hemminger208.13%450.00%
Total246100.00%8100.00%

/* Track delayed acknowledgment ratio using sliding window * ratio = (15*ratio + sample) / 16 */
static void bictcp_acked(struct sock *sk, const struct ack_sample *sample) { const struct tcp_sock *tp = tcp_sk(sk); struct bictcp *ca = inet_csk_ca(sk); u32 delay; /* Some calls are for duplicates without timetamps */ if (sample->rtt_us < 0) return; /* Discard delay samples right after fast recovery */ if (ca->epoch_start && (s32)(tcp_time_stamp - ca->epoch_start) < HZ) return; delay = (sample->rtt_us << 3) / USEC_PER_MSEC; 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 (hystart && tcp_in_slow_start(tp) && tp->snd_cwnd >= hystart_low_window) hystart_update(sk, delay); }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger9367.39%342.86%
Sangtae Ha2921.01%114.29%
Lawrence Brakmo96.52%114.29%
Eric Dumazet42.90%114.29%
Yuchung Cheng32.17%114.29%
Total138100.00%7100.00%

static struct tcp_congestion_ops cubictcp __read_mostly = { .init = bictcp_init, .ssthresh = bictcp_recalc_ssthresh, .cong_avoid = bictcp_cong_avoid, .set_state = bictcp_state, .undo_cwnd = bictcp_undo_cwnd, .cwnd_event = bictcp_cwnd_event, .pkts_acked = bictcp_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); }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger7998.75%375.00%
Alexey Dobriyan11.25%125.00%
Total80100.00%4100.00%


static void __exit cubictcp_unregister(void) { tcp_unregister_congestion_control(&cubictcp); }

Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger15100.00%1100.00%
Total15100.00%1100.00%

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");

Overall Contributors

PersonTokensPropCommitsCommitProp
Stephen Hemminger152867.79%1336.11%
Sangtae Ha43619.34%411.11%
Eric Dumazet2018.92%719.44%
Neal Cardwell622.75%513.89%
Lawrence Brakmo90.40%12.78%
Yuchung Cheng90.40%25.56%
Ilpo Järvinen40.18%12.78%
Roman Zippel30.13%12.78%
Alexey Dobriyan10.04%12.78%
Hideaki Yoshifuji / 吉藤英明10.04%12.78%
Total2254100.00%36100.00%
Directory: net/ipv4
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