| /* |
| * TCP CUBIC: Binary Increase Congestion control for TCP v2.0 |
| * |
| * This is from the implementation of CUBIC TCP in |
| * Injong Rhee, Lisong Xu. |
| * "CUBIC: A New TCP-Friendly High-Speed TCP Variant |
| * in PFLDnet 2005 |
| * Available from: |
| * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf |
| * |
| * Unless CUBIC is enabled and congestion window is large |
| * this behaves the same as the original Reno. |
| */ |
| |
| #include <linux/config.h> |
| #include <linux/mm.h> |
| #include <linux/module.h> |
| #include <net/tcp.h> |
| #include <asm/div64.h> |
| |
| #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation |
| * max_cwnd = snd_cwnd * beta |
| */ |
| #define BICTCP_B 4 /* |
| * In binary search, |
| * go to point (max+min)/N |
| */ |
| #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */ |
| |
| static int fast_convergence = 1; |
| static int max_increment = 16; |
| static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ |
| static int initial_ssthresh = 100; |
| static int bic_scale = 41; |
| static int tcp_friendliness = 1; |
| |
| static u32 cube_rtt_scale; |
| static u32 beta_scale; |
| static u64 cube_factor; |
| |
| /* 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(max_increment, int, 0644); |
| MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); |
| module_param(beta, int, 0444); |
| 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"); |
| |
| |
| /* 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 */ |
| u32 epoch_start; /* beginning of an epoch */ |
| u32 ack_cnt; /* number of acks */ |
| u32 tcp_cwnd; /* estimated tcp cwnd */ |
| #define ACK_RATIO_SHIFT 4 |
| u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ |
| }; |
| |
| static inline void bictcp_reset(struct bictcp *ca) |
| { |
| ca->cnt = 0; |
| ca->last_max_cwnd = 0; |
| ca->loss_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->delayed_ack = 2 << ACK_RATIO_SHIFT; |
| ca->ack_cnt = 0; |
| ca->tcp_cwnd = 0; |
| } |
| |
| static void bictcp_init(struct sock *sk) |
| { |
| bictcp_reset(inet_csk_ca(sk)); |
| if (initial_ssthresh) |
| tcp_sk(sk)->snd_ssthresh = initial_ssthresh; |
| } |
| |
| /* 65536 times the cubic root */ |
| static const u64 cubic_table[8] |
| = {0, 65536, 82570, 94519, 104030, 112063, 119087, 125367}; |
| |
| /* |
| * calculate the cubic root of x |
| * the basic idea is that x can be expressed as i*8^j |
| * so cubic_root(x) = cubic_root(i)*2^j |
| * in the following code, x is i, and y is 2^j |
| * because of integer calculation, there are errors in calculation |
| * so finally use binary search to find out the exact solution |
| */ |
| static u32 cubic_root(u64 x) |
| { |
| u64 y, app, target, start, end, mid, start_diff, end_diff; |
| |
| if (x == 0) |
| return 0; |
| |
| target = x; |
| |
| /* first estimate lower and upper bound */ |
| y = 1; |
| while (x >= 8){ |
| x = (x >> 3); |
| y = (y << 1); |
| } |
| start = (y*cubic_table[x])>>16; |
| if (x==7) |
| end = (y<<1); |
| else |
| end = (y*cubic_table[x+1]+65535)>>16; |
| |
| /* binary search for more accurate one */ |
| while (start < end-1) { |
| mid = (start+end) >> 1; |
| app = mid*mid*mid; |
| if (app < target) |
| start = mid; |
| else if (app > target) |
| end = mid; |
| else |
| return mid; |
| } |
| |
| /* find the most accurate one from start and end */ |
| app = start*start*start; |
| if (app < target) |
| start_diff = target - app; |
| else |
| start_diff = app - target; |
| app = end*end*end; |
| if (app < target) |
| end_diff = target - app; |
| else |
| end_diff = app - target; |
| |
| if (start_diff < end_diff) |
| return (u32)start; |
| else |
| return (u32)end; |
| } |
| |
| /* |
| * Compute congestion window to use. |
| */ |
| static inline void bictcp_update(struct bictcp *ca, u32 cwnd) |
| { |
| u64 offs; |
| u32 delta, t, bic_target, min_cnt, max_cnt; |
| |
| ca->ack_cnt++; /* count the number of ACKs */ |
| |
| if (ca->last_cwnd == cwnd && |
| (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) |
| return; |
| |
| ca->last_cwnd = cwnd; |
| ca->last_time = tcp_time_stamp; |
| |
| if (ca->epoch_start == 0) { |
| ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */ |
| ca->ack_cnt = 1; /* 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 !!! |
| */ |
| |
| /* change the unit from HZ to bictcp_HZ */ |
| t = ((tcp_time_stamp + ca->delay_min - ca->epoch_start) |
| << BICTCP_HZ) / 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*/ |
| } |
| |
| if (ca->delay_min > 0) { |
| /* max increment = Smax * rtt / 0.1 */ |
| min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min); |
| if (ca->cnt < min_cnt) |
| ca->cnt = min_cnt; |
| } |
| |
| /* slow start and low utilization */ |
| if (ca->loss_cwnd == 0) /* could be aggressive in slow start */ |
| ca->cnt = 50; |
| |
| /* 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; |
| } |
| } |
| |
| ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; |
| if (ca->cnt == 0) /* cannot be zero */ |
| ca->cnt = 1; |
| } |
| |
| |
| /* Keep track of minimum rtt */ |
| static inline void measure_delay(struct sock *sk) |
| { |
| const struct tcp_sock *tp = tcp_sk(sk); |
| struct bictcp *ca = inet_csk_ca(sk); |
| u32 delay; |
| |
| /* No time stamp */ |
| if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) || |
| /* Discard delay samples right after fast recovery */ |
| (s32)(tcp_time_stamp - ca->epoch_start) < HZ) |
| return; |
| |
| delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr; |
| 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; |
| } |
| |
| static void bictcp_cong_avoid(struct sock *sk, u32 ack, |
| u32 seq_rtt, u32 in_flight, int data_acked) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct bictcp *ca = inet_csk_ca(sk); |
| |
| if (data_acked) |
| measure_delay(sk); |
| |
| if (!tcp_is_cwnd_limited(sk, in_flight)) |
| return; |
| |
| if (tp->snd_cwnd <= tp->snd_ssthresh) |
| tcp_slow_start(tp); |
| else { |
| bictcp_update(ca, tp->snd_cwnd); |
| |
| /* In dangerous area, increase slowly. |
| * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd |
| */ |
| if (tp->snd_cwnd_cnt >= ca->cnt) { |
| if (tp->snd_cwnd < tp->snd_cwnd_clamp) |
| tp->snd_cwnd++; |
| tp->snd_cwnd_cnt = 0; |
| } else |
| tp->snd_cwnd_cnt++; |
| } |
| |
| } |
| |
| 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); |
| } |
| |
| static u32 bictcp_undo_cwnd(struct sock *sk) |
| { |
| struct bictcp *ca = inet_csk_ca(sk); |
| |
| return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd); |
| } |
| |
| static u32 bictcp_min_cwnd(struct sock *sk) |
| { |
| return tcp_sk(sk)->snd_ssthresh; |
| } |
| |
| static void bictcp_state(struct sock *sk, u8 new_state) |
| { |
| if (new_state == TCP_CA_Loss) |
| bictcp_reset(inet_csk_ca(sk)); |
| } |
| |
| /* Track delayed acknowledgment ratio using sliding window |
| * ratio = (15*ratio + sample) / 16 |
| */ |
| static void bictcp_acked(struct sock *sk, u32 cnt) |
| { |
| const struct inet_connection_sock *icsk = inet_csk(sk); |
| |
| if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) { |
| struct bictcp *ca = inet_csk_ca(sk); |
| cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; |
| ca->delayed_ack += cnt; |
| } |
| } |
| |
| |
| static struct tcp_congestion_ops cubictcp = { |
| .init = bictcp_init, |
| .ssthresh = bictcp_recalc_ssthresh, |
| .cong_avoid = bictcp_cong_avoid, |
| .set_state = bictcp_state, |
| .undo_cwnd = bictcp_undo_cwnd, |
| .min_cwnd = bictcp_min_cwnd, |
| .pkts_acked = bictcp_acked, |
| .owner = THIS_MODULE, |
| .name = "cubic", |
| }; |
| |
| static int __init cubictcp_register(void) |
| { |
| 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 << 3) / 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("2.0"); |