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Diffstat (limited to '')
-rw-r--r-- | net/ipv4/tcp_cubic.c | 557 |
1 files changed, 557 insertions, 0 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c new file mode 100644 index 000000000..768c10c1f --- /dev/null +++ b/net/ipv4/tcp_cubic.c @@ -0,0 +1,557 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * 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/btf.h> +#include <linux/btf_ids.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 (4000U) /* 4 ms */ +#define HYSTART_DELAY_MAX (16000U) /* 16 ms */ +#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_us __read_mostly = 2000; + +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, "hybrid 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_us, int, 0644); +MODULE_PARM_DESC(hystart_ack_delta_us, "spacing between ack's indicating train (usecs)"); + +/* BIC TCP Parameters */ +struct bictcp { + u32 cnt; /* increase cwnd by 1 after ACKs */ + u32 last_max_cwnd; /* last maximum snd_cwnd */ + 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 (usec) */ + 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) +{ + memset(ca, 0, offsetof(struct bictcp, unused)); + ca->found = 0; +} + +static inline u32 bictcp_clock_us(const struct sock *sk) +{ + return tcp_sk(sk)->tcp_mstamp; +} + +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_us(sk); + ca->end_seq = tp->snd_nxt; + ca->curr_rtt = ~0U; + ca->sample_cnt = 0; +} + +static void cubictcp_init(struct sock *sk) +{ + struct bictcp *ca = inet_csk_ca(sk); + + bictcp_reset(ca); + + if (hystart) + bictcp_hystart_reset(sk); + + if (!hystart && initial_ssthresh) + tcp_sk(sk)->snd_ssthresh = initial_ssthresh; +} + +static void cubictcp_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_jiffies32; + 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; + } +} + +/* 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; +} + +/* + * 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_jiffies32 - 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_jiffies32 == ca->last_time) + goto tcp_friendliness; + + ca->last_cwnd = cwnd; + ca->last_time = tcp_jiffies32; + + if (ca->epoch_start == 0) { + ca->epoch_start = tcp_jiffies32; /* 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_jiffies32 - ca->epoch_start); + t += usecs_to_jiffies(ca->delay_min); + /* 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); +} + +static void cubictcp_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)) { + acked = tcp_slow_start(tp, acked); + if (!acked) + return; + } + bictcp_update(ca, tcp_snd_cwnd(tp), acked); + tcp_cong_avoid_ai(tp, ca->cnt, acked); +} + +static u32 cubictcp_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 (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence) + ca->last_max_cwnd = (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta)) + / (2 * BICTCP_BETA_SCALE); + else + ca->last_max_cwnd = tcp_snd_cwnd(tp); + + return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U); +} + +static void cubictcp_state(struct sock *sk, u8 new_state) +{ + if (new_state == TCP_CA_Loss) { + bictcp_reset(inet_csk_ca(sk)); + bictcp_hystart_reset(sk); + } +} + +/* Account for TSO/GRO delays. + * Otherwise short RTT flows could get too small ssthresh, since during + * slow start we begin with small TSO packets and ca->delay_min would + * not account for long aggregation delay when TSO packets get bigger. + * Ideally even with a very small RTT we would like to have at least one + * TSO packet being sent and received by GRO, and another one in qdisc layer. + * We apply another 100% factor because @rate is doubled at this point. + * We cap the cushion to 1ms. + */ +static u32 hystart_ack_delay(const struct sock *sk) +{ + unsigned long rate; + + rate = READ_ONCE(sk->sk_pacing_rate); + if (!rate) + return 0; + return min_t(u64, USEC_PER_MSEC, + div64_ul((u64)sk->sk_gso_max_size * 4 * USEC_PER_SEC, rate)); +} + +static void hystart_update(struct sock *sk, u32 delay) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct bictcp *ca = inet_csk_ca(sk); + u32 threshold; + + if (after(tp->snd_una, ca->end_seq)) + bictcp_hystart_reset(sk); + + if (hystart_detect & HYSTART_ACK_TRAIN) { + u32 now = bictcp_clock_us(sk); + + /* first detection parameter - ack-train detection */ + if ((s32)(now - ca->last_ack) <= hystart_ack_delta_us) { + ca->last_ack = now; + + threshold = ca->delay_min + hystart_ack_delay(sk); + + /* Hystart ack train triggers if we get ack past + * ca->delay_min/2. + * Pacing might have delayed packets up to RTT/2 + * during slow start. + */ + if (sk->sk_pacing_status == SK_PACING_NONE) + threshold >>= 1; + + if ((s32)(now - ca->round_start) > threshold) { + ca->found = 1; + pr_debug("hystart_ack_train (%u > %u) delay_min %u (+ ack_delay %u) cwnd %u\n", + now - ca->round_start, threshold, + ca->delay_min, hystart_ack_delay(sk), tcp_snd_cwnd(tp)); + NET_INC_STATS(sock_net(sk), + LINUX_MIB_TCPHYSTARTTRAINDETECT); + NET_ADD_STATS(sock_net(sk), + LINUX_MIB_TCPHYSTARTTRAINCWND, + tcp_snd_cwnd(tp)); + tp->snd_ssthresh = tcp_snd_cwnd(tp); + } + } + } + + if (hystart_detect & HYSTART_DELAY) { + /* obtain the minimum delay of more than sampling packets */ + if (ca->curr_rtt > delay) + ca->curr_rtt = delay; + if (ca->sample_cnt < HYSTART_MIN_SAMPLES) { + ca->sample_cnt++; + } else { + if (ca->curr_rtt > ca->delay_min + + HYSTART_DELAY_THRESH(ca->delay_min >> 3)) { + ca->found = 1; + NET_INC_STATS(sock_net(sk), + LINUX_MIB_TCPHYSTARTDELAYDETECT); + NET_ADD_STATS(sock_net(sk), + LINUX_MIB_TCPHYSTARTDELAYCWND, + tcp_snd_cwnd(tp)); + tp->snd_ssthresh = tcp_snd_cwnd(tp); + } + } + } +} + +static void cubictcp_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_jiffies32 - ca->epoch_start) < HZ) + return; + + 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 && + tcp_snd_cwnd(tp) >= 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", +}; + +BTF_SET8_START(tcp_cubic_check_kfunc_ids) +#ifdef CONFIG_X86 +#ifdef CONFIG_DYNAMIC_FTRACE +BTF_ID_FLAGS(func, cubictcp_init) +BTF_ID_FLAGS(func, cubictcp_recalc_ssthresh) +BTF_ID_FLAGS(func, cubictcp_cong_avoid) +BTF_ID_FLAGS(func, cubictcp_state) +BTF_ID_FLAGS(func, cubictcp_cwnd_event) +BTF_ID_FLAGS(func, cubictcp_acked) +#endif +#endif +BTF_SET8_END(tcp_cubic_check_kfunc_ids) + +static const struct btf_kfunc_id_set tcp_cubic_kfunc_set = { + .owner = THIS_MODULE, + .set = &tcp_cubic_check_kfunc_ids, +}; + +static int __init cubictcp_register(void) +{ + int ret; + + 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); + + ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_cubic_kfunc_set); + if (ret < 0) + return ret; + 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"); |