Replace existing BIC version 1.1 with new version 2.0. The main change is to replace the window growth function with a cubic function as described in: http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]> --- bic-2.6.orig/net/ipv4/tcp_bic.c +++ bic-2.6/net/ipv4/tcp_bic.c @@ -1,12 +1,12 @@ /* - * Binary Increase Congestion control for TCP + * Binary Increase Congestion control for TCP v2.0 * - * This is from the implementation of BICTCP in - * Lison-Xu, Kahaled Harfoush, and Injong Rhee. - * "Binary Increase Congestion Control for Fast, Long Distance - * Networks" in InfoComm 2004 + * 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.pdf + * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf * * Unless BIC is enabled and congestion window is large * this behaves the same as the original Reno. @@ -25,26 +25,27 @@ * 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 low_window = 14; static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ static int initial_ssthresh = 100; -static int smooth_part = 20; +static int bic_scale = 41; +static int tcp_friendliness = 1; 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(low_window, int, 0644); -MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)"); 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(smooth_part, int, 0644); -MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax"); +module_param(bic_scale, int, 0644); +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 */ @@ -54,7 +55,12 @@ struct bictcp { 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 */ }; @@ -66,8 +72,13 @@ static inline void bictcp_reset(struct b 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) @@ -77,11 +88,131 @@ static void bictcp_init(struct sock *sk) 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; +} + +static inline u32 bictcp_K(u32 dist, u32 srtt) +{ + u64 d64; + u32 d32; + u32 count; + u32 result; + + /* 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 = (tp->srtt >> 3 ) / HZ + + 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 */ + d32 = (1 << (10+2*BICTCP_HZ)) / bic_scale; + d64 = (__u64)d32; + + /* srtt * 2^count / HZ + 1) to get a better accuracy of the following d32, + the larger the "count", the better the accuracy + 2) and avoid overflow of the following d64 + the larger the "count", the high possibility of overflow + 3) so find a "count" between bictcp_hz-3 and bictcp_hz + "count" may be less than bictcp_HZ, + then d64 becomes 0. that is OK + */ + d32 = srtt; + count = 0; + while (((d32 & 0x80000000)==0) && (count < BICTCP_HZ)){ + d32 = d32 << 1; + count++; + } + d32 = d32 / HZ; + + /* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) */ + d64 = (d64 * dist * d32) >> (count+3-BICTCP_HZ); + + /* cubic root */ + d64 = cubic_root(d64); + + result = (u32)d64; + return result; +} + /* * Compute congestion window to use. */ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) { + u64 d64; + u32 d32, t, srtt, 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; @@ -89,60 +220,126 @@ static inline void bictcp_update(struct ca->last_cwnd = cwnd; ca->last_time = tcp_time_stamp; - if (ca->epoch_start == 0) /* record the beginning of an epoch */ - ca->epoch_start = tcp_time_stamp; + srtt = (HZ << 3)/10; /* use real time-based growth function */ - /* start off normal */ - if (cwnd <= low_window) { - ca->cnt = cwnd; - return; + 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 { + ca->bic_K = bictcp_K(ca->last_max_cwnd-cwnd, srtt); + ca->bic_origin_point = ca->last_max_cwnd; + } } - /* binary increase */ - if (cwnd < ca->last_max_cwnd) { - __u32 dist = (ca->last_max_cwnd - cwnd) - / BICTCP_B; - - if (dist > max_increment) - /* linear increase */ - ca->cnt = cwnd / max_increment; - else if (dist <= 1U) - /* binary search increase */ - ca->cnt = (cwnd * smooth_part) / BICTCP_B; - else - /* binary search increase */ - ca->cnt = cwnd / dist; - } else { - /* slow start AMD linear increase */ - if (cwnd < ca->last_max_cwnd + BICTCP_B) - /* slow start */ - ca->cnt = (cwnd * smooth_part) / BICTCP_B; - else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1)) - /* slow start */ - ca->cnt = (cwnd * (BICTCP_B-1)) - / (cwnd - ca->last_max_cwnd); - else - /* linear increase */ - ca->cnt = cwnd / max_increment; + /* cubic function - calc*/ + /* calculate c * time^3 / rtt, + * while considering overflow in calculation of time^3 + * (so time^3 is done by using d64) + * and without the support of division of 64bit numbers + * (so all divisions are done by using d32) + * 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 */ + d32 = ca->bic_K - t; + else + d32 = t - ca->bic_K; + + d64 = (u64)d32; + d32 = (bic_scale << 3) * HZ / srtt; /* 1024*c/rtt */ + d64 = (d32 * d64 * d64 * d64) >> (10+3*BICTCP_HZ); /* c/rtt * (t-K)^3 */ + d32 = (u32)d64; + if (t < ca->bic_K) /* below origin*/ + bic_target = ca->bic_origin_point - d32; + else /* above origin*/ + bic_target = ca->bic_origin_point + d32; + + /* 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; } - /* if in slow start or link utilization is very low */ - if (ca->loss_cwnd == 0) { - if (ca->cnt > 20) /* increase cwnd 5% per RTT */ - ca->cnt = 20; - } + /* 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 = 8*(BICTCP_BETA_SCALE+beta)/3/(BICTCP_BETA_SCALE-beta); + d32 = (cwnd * scale) >> 3; + while (ca->ack_cnt > d32) { /* update tcp cwnd */ + ca->ack_cnt -= d32; + ca->tcp_cwnd++; + } + + if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */ + d32 = ca->tcp_cwnd - cwnd; + max_cnt = cwnd / d32; + 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; @@ -164,10 +361,6 @@ static void bictcp_cong_avoid(struct soc } -/* - * behave like Reno until low_window is reached, - * then increase congestion window slowly - */ static u32 bictcp_recalc_ssthresh(struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); @@ -184,24 +377,19 @@ static u32 bictcp_recalc_ssthresh(struct ca->loss_cwnd = tp->snd_cwnd; - - if (tp->snd_cwnd <= low_window) - return max(tp->snd_cwnd >> 1U, 2U); - else - return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); + return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); } static u32 bictcp_undo_cwnd(struct sock *sk) { - const struct tcp_sock *tp = tcp_sk(sk); - const struct bictcp *ca = inet_csk_ca(sk); - return max(tp->snd_cwnd, ca->last_max_cwnd); + 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) { - const struct tcp_sock *tp = tcp_sk(sk); - return tp->snd_ssthresh; + return tcp_sk(sk)->snd_ssthresh; } static void bictcp_state(struct sock *sk, u8 new_state) @@ -251,6 +439,7 @@ static void __exit bictcp_unregister(voi module_init(bictcp_register); module_exit(bictcp_unregister); -MODULE_AUTHOR("Stephen Hemminger"); +MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("BIC TCP"); +MODULE_VERSION("2.0"); -- Stephen Hemminger <[EMAIL PROTECTED]> OSDL http://developer.osdl.org/~shemminger - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
