X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=net%2Fipv4%2Ftcp_cubic.c;h=71d5f2f29fa62b92cb4ae4d4762b5322d017f5d3;hb=631330f5847b3f8a7ea67d689e9f7c56833ccaa6;hp=6f08adbda54e3e198b86632152bb53b01d8b6cef;hpb=3927f2e8f9afa3424bb51ca81f7abac01ffd0005;p=safe%2Fjmp%2Flinux-2.6 diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index 6f08adb..71d5f2f 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -1,12 +1,23 @@ /* - * TCP CUBIC: Binary Increase Congestion control for TCP v2.0 - * + * 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 - * Injong Rhee, Lisong Xu. - * "CUBIC: A New TCP-Friendly High-Speed TCP Variant - * in PFLDnet 2005 + * 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://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf + * 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. @@ -14,25 +25,34 @@ #include #include +#include #include -#include #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 */ +/* 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 (2U<<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 max_increment __read_mostly = 16; -static int beta __read_mostly = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ -static int initial_ssthresh __read_mostly = 100; +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 u32 cube_rtt_scale __read_mostly; static u32 beta_scale __read_mostly; static u64 cube_factor __read_mostly; @@ -40,9 +60,7 @@ 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(max_increment, int, 0644); -MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); -module_param(beta, int, 0444); +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"); @@ -50,6 +68,13 @@ 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"); /* BIC TCP Parameters */ struct bictcp { @@ -65,7 +90,13 @@ struct bictcp { 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 */ + u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ + 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_jiffies; /* 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) @@ -82,38 +113,76 @@ static inline void bictcp_reset(struct bictcp *ca) ca->delayed_ack = 2 << ACK_RATIO_SHIFT; ca->ack_cnt = 0; ca->tcp_cwnd = 0; + ca->found = 0; +} + +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_jiffies = jiffies; + ca->end_seq = tp->snd_nxt; + ca->curr_rtt = 0; + ca->sample_cnt = 0; } static void bictcp_init(struct sock *sk) { bictcp_reset(inet_csk_ca(sk)); - if (initial_ssthresh) + + if (hystart) + bictcp_hystart_reset(sk); + + if (!hystart && initial_ssthresh) tcp_sk(sk)->snd_ssthresh = initial_ssthresh; } -/* - * calculate the cubic root of x using Newton-Raphson +/* 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, x1; - - /* Initial estimate is based on: - * cbrt(x) = exp(log(x) / 3) + 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 */ - x = 1u << (fls64(a)/3); + 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; /* - * Iteration based on: + * Newton-Raphson iteration * 2 * x = ( 2 * x + a / x ) / 3 * k+1 k k */ - do { - x1 = x; - x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3; - } while (abs(x1 - x) > 1); - + x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1))); + x = ((x * 341) >> 10); return x; } @@ -123,7 +192,7 @@ static u32 cubic_root(u64 a) static inline void bictcp_update(struct bictcp *ca, u32 cwnd) { u64 offs; - u32 delta, t, bic_target, min_cnt, max_cnt; + u32 delta, t, bic_target, max_cnt; ca->ack_cnt++; /* count the number of ACKs */ @@ -189,17 +258,6 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 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; @@ -222,55 +280,21 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 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)<<3; - 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) +static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) { 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) + if (tp->snd_cwnd <= tp->snd_ssthresh) { + if (hystart && after(ack, ca->end_seq)) + bictcp_hystart_reset(sk); tcp_slow_start(tp); - else { + } 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++; + tcp_cong_avoid_ai(tp, ca->cnt); } } @@ -303,24 +327,83 @@ static u32 bictcp_undo_cwnd(struct sock *sk) static void bictcp_state(struct sock *sk, u8 new_state) { - if (new_state == TCP_CA_Loss) + if (new_state == TCP_CA_Loss) { bictcp_reset(inet_csk_ca(sk)); + bictcp_hystart_reset(sk); + } +} + +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)) { + u32 curr_jiffies = jiffies; + + /* first detection parameter - ack-train detection */ + if (curr_jiffies - ca->last_jiffies <= msecs_to_jiffies(2)) { + ca->last_jiffies = curr_jiffies; + if (curr_jiffies - ca->round_start >= ca->delay_min>>4) + ca->found |= HYSTART_ACK_TRAIN; + } + + /* 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>>4)) + ca->found |= HYSTART_DELAY; + } + /* + * Either one of two conditions are met, + * we exit from slow start immediately. + */ + if (ca->found & hystart_detect) + tp->snd_ssthresh = tp->snd_cwnd; + } } /* Track delayed acknowledgment ratio using sliding window * ratio = (15*ratio + sample) / 16 */ -static void bictcp_acked(struct sock *sk, u32 cnt) +static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) { const struct inet_connection_sock *icsk = inet_csk(sk); + const struct tcp_sock *tp = tcp_sk(sk); + struct bictcp *ca = inet_csk_ca(sk); + u32 delay; - if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) { - struct bictcp *ca = inet_csk_ca(sk); + if (icsk->icsk_ca_state == TCP_CA_Open) { cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; ca->delayed_ack += cnt; } -} + /* Some calls are for duplicates without timetamps */ + if (rtt_us < 0) + return; + + /* Discard delay samples right after fast recovery */ + if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ) + return; + + delay = usecs_to_jiffies(rtt_us) << 3; + 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 && tp->snd_cwnd <= tp->snd_ssthresh && + tp->snd_cwnd >= hystart_low_window) + hystart_update(sk, delay); +} static struct tcp_congestion_ops cubictcp = { .init = bictcp_init, @@ -378,4 +461,4 @@ module_exit(cubictcp_unregister); MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("CUBIC TCP"); -MODULE_VERSION("2.0"); +MODULE_VERSION("2.3");