LCOV - code coverage report
Current view: top level - net/ipv4 - tcp_cubic.c (source / functions) Hit Total Coverage
Test: coverage.info Lines: 187 187 100.0 %
Date: 2017-01-25 Functions: 13 13 100.0 %

          Line data    Source code
       1             : /*
       2             :  * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
       3             :  * Home page:
       4             :  *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
       5             :  * This is from the implementation of CUBIC TCP in
       6             :  * Sangtae Ha, Injong Rhee and Lisong Xu,
       7             :  *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
       8             :  *  in ACM SIGOPS Operating System Review, July 2008.
       9             :  * Available from:
      10             :  *  http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
      11             :  *
      12             :  * CUBIC integrates a new slow start algorithm, called HyStart.
      13             :  * The details of HyStart are presented in
      14             :  *  Sangtae Ha and Injong Rhee,
      15             :  *  "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
      16             :  * Available from:
      17             :  *  http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
      18             :  *
      19             :  * All testing results are available from:
      20             :  * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
      21             :  *
      22             :  * Unless CUBIC is enabled and congestion window is large
      23             :  * this behaves the same as the original Reno.
      24             :  */
      25             : 
      26             : #include <linux/mm.h>
      27             : #include <linux/module.h>
      28             : #include <linux/math64.h>
      29             : #include <net/tcp.h>
      30             : 
      31             : #define BICTCP_BETA_SCALE    1024       /* Scale factor beta calculation
      32             :                                          * max_cwnd = snd_cwnd * beta
      33             :                                          */
      34             : #define BICTCP_HZ               10      /* BIC HZ 2^10 = 1024 */
      35             : 
      36             : /* Two methods of hybrid slow start */
      37             : #define HYSTART_ACK_TRAIN       0x1
      38             : #define HYSTART_DELAY           0x2
      39             : 
      40             : /* Number of delay samples for detecting the increase of delay */
      41             : #define HYSTART_MIN_SAMPLES     8
      42             : #define HYSTART_DELAY_MIN       (2U<<3)
      43             : #define HYSTART_DELAY_MAX       (16U<<3)
      44             : #define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
      45             : 
      46           1 : static int fast_convergence __read_mostly = 1;
      47           1 : static int beta __read_mostly = 717;    /* = 717/1024 (BICTCP_BETA_SCALE) */
      48           1 : static int initial_ssthresh __read_mostly;
      49           1 : static int bic_scale __read_mostly = 41;
      50           1 : static int tcp_friendliness __read_mostly = 1;
      51             : 
      52           1 : static int hystart __read_mostly = 1;
      53           1 : static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
      54           1 : static int hystart_low_window __read_mostly = 16;
      55             : 
      56           1 : static u32 cube_rtt_scale __read_mostly;
      57           1 : static u32 beta_scale __read_mostly;
      58           1 : static u64 cube_factor __read_mostly;
      59             : 
      60             : /* Note parameters that are used for precomputing scale factors are read-only */
      61             : module_param(fast_convergence, int, 0644);
      62             : MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
      63             : module_param(beta, int, 0644);
      64             : MODULE_PARM_DESC(beta, "beta for multiplicative increase");
      65             : module_param(initial_ssthresh, int, 0644);
      66             : MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
      67             : module_param(bic_scale, int, 0444);
      68             : MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
      69             : module_param(tcp_friendliness, int, 0644);
      70             : MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
      71             : module_param(hystart, int, 0644);
      72             : MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
      73             : module_param(hystart_detect, int, 0644);
      74             : MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms"
      75             :                  " 1: packet-train 2: delay 3: both packet-train and delay");
      76             : module_param(hystart_low_window, int, 0644);
      77           1 : MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
      78             : 
      79             : /* BIC TCP Parameters */
      80             : struct bictcp {
      81             :         u32     cnt;            /* increase cwnd by 1 after ACKs */
      82             :         u32     last_max_cwnd;  /* last maximum snd_cwnd */
      83             :         u32     loss_cwnd;      /* congestion window at last loss */
      84             :         u32     last_cwnd;      /* the last snd_cwnd */
      85             :         u32     last_time;      /* time when updated last_cwnd */
      86             :         u32     bic_origin_point;/* origin point of bic function */
      87             :         u32     bic_K;          /* time to origin point from the beginning of the current epoch */
      88             :         u32     delay_min;      /* min delay */
      89             :         u32     epoch_start;    /* beginning of an epoch */
      90             :         u32     ack_cnt;        /* number of acks */
      91             :         u32     tcp_cwnd;       /* estimated tcp cwnd */
      92             : #define ACK_RATIO_SHIFT 4
      93             :         u16     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
      94             :         u8      sample_cnt;     /* number of samples to decide curr_rtt */
      95             :         u8      found;          /* the exit point is found? */
      96             :         u32     round_start;    /* beginning of each round */
      97             :         u32     end_seq;        /* end_seq of the round */
      98             :         u32     last_jiffies;   /* last time when the ACK spacing is close */
      99             :         u32     curr_rtt;       /* the minimum rtt of current round */
     100             : };
     101             : 
     102             : static inline void bictcp_reset(struct bictcp *ca)
     103             : {
     104           2 :         ca->cnt = 0;
     105           2 :         ca->last_max_cwnd = 0;
     106           2 :         ca->loss_cwnd = 0;
     107           2 :         ca->last_cwnd = 0;
     108           2 :         ca->last_time = 0;
     109           2 :         ca->bic_origin_point = 0;
     110           2 :         ca->bic_K = 0;
     111           2 :         ca->delay_min = 0;
     112           2 :         ca->epoch_start = 0;
     113           2 :         ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
     114           2 :         ca->ack_cnt = 0;
     115           2 :         ca->tcp_cwnd = 0;
     116           2 :         ca->found = 0;
     117           2 : }
     118             : 
     119             : static inline void bictcp_hystart_reset(struct sock *sk)
     120             : {
     121          12 :         struct tcp_sock *tp = tcp_sk(sk);
     122          12 :         struct bictcp *ca = inet_csk_ca(sk);
     123           3 : 
     124          12 :         ca->round_start = ca->last_jiffies = jiffies;
     125           6 :         ca->end_seq = tp->snd_nxt;
     126           3 :         ca->curr_rtt = 0;
     127           3 :         ca->sample_cnt = 0;
     128           3 : }
     129             : 
     130             : static void bictcp_init(struct sock *sk)
     131             : {
     132           5 :         bictcp_reset(inet_csk_ca(sk));
     133           1 : 
     134           2 :         if (hystart)
     135           2 :                 bictcp_hystart_reset(sk);
     136             : 
     137           8 :         if (!hystart && initial_ssthresh)
     138           5 :                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
     139           3 : }
     140             : 
     141             : /* calculate the cubic root of x using a table lookup followed by one
     142             :  * Newton-Raphson iteration.
     143             :  * Avg err ~= 0.195%
     144             :  */
     145             : static u32 cubic_root(u64 a)
     146             : {
     147           1 :         u32 x, b, shift;
     148           1 :         /*
     149           1 :          * cbrt(x) MSB values for x MSB values in [0..63].
     150           1 :          * Precomputed then refined by hand - Willy Tarreau
     151           1 :          *
     152           1 :          * For x in [0..63],
     153             :          *   v = cbrt(x << 18) - 1
     154             :          *   cbrt(x) = (v[x] + 10) >> 6
     155             :          */
     156          64 :         static const u8 v[] = {
     157             :                 /* 0x00 */    0,   54,   54,   54,  118,  118,  118,  118,
     158             :                 /* 0x08 */  123,  129,  134,  138,  143,  147,  151,  156,
     159             :                 /* 0x10 */  157,  161,  164,  168,  170,  173,  176,  179,
     160             :                 /* 0x18 */  181,  185,  187,  190,  192,  194,  197,  199,
     161             :                 /* 0x20 */  200,  202,  204,  206,  209,  211,  213,  215,
     162             :                 /* 0x28 */  217,  219,  221,  222,  224,  225,  227,  229,
     163             :                 /* 0x30 */  231,  232,  234,  236,  237,  239,  240,  242,
     164             :                 /* 0x38 */  244,  245,  246,  248,  250,  251,  252,  254,
     165             :         };
     166             : 
     167           4 :         b = fls64(a);
     168           2 :         if (b < 7) {
     169             :                 /* a in [0..63] */
     170           1 :                 return ((u32)v[(u32)a] + 35) >> 6;
     171             :         }
     172             : 
     173           1 :         b = ((b * 84) >> 8) - 1;
     174           1 :         shift = (a >> (b * 3));
     175             : 
     176           1 :         x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
     177             : 
     178             :         /*
     179             :          * Newton-Raphson iteration
     180             :          *                         2
     181             :          * x    = ( 2 * x  +  a / x  ) / 3
     182             :          *  k+1          k         k
     183             :          */
     184           3 :         x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
     185           1 :         x = ((x * 341) >> 10);
     186           1 :         return x;
     187             : }
     188             : 
     189             : /*
     190             :  * Compute congestion window to use.
     191             :  */
     192             : static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
     193             : {
     194           1 :         u64 offs;
     195           1 :         u32 delta, t, bic_target, max_cnt;
     196           1 : 
     197           2 :         ca->ack_cnt++;       /* count the number of ACKs */
     198           1 : 
     199           5 :         if (ca->last_cwnd == cwnd &&
     200             :             (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
     201           1 :                 return;
     202             : 
     203           1 :         ca->last_cwnd = cwnd;
     204           1 :         ca->last_time = tcp_time_stamp;
     205             : 
     206           2 :         if (ca->epoch_start == 0) {
     207           1 :                 ca->epoch_start = tcp_time_stamp;    /* record the beginning of an epoch */
     208           1 :                 ca->ack_cnt = 1;                     /* start counting */
     209           1 :                 ca->tcp_cwnd = cwnd;                 /* syn with cubic */
     210             : 
     211           2 :                 if (ca->last_max_cwnd <= cwnd) {
     212           1 :                         ca->bic_K = 0;
     213           1 :                         ca->bic_origin_point = cwnd;
     214             :                 } else {
     215             :                         /* Compute new K based on
     216             :                          * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
     217             :                          */
     218           3 :                         ca->bic_K = cubic_root(cube_factor
     219             :                                                * (ca->last_max_cwnd - cwnd));
     220           1 :                         ca->bic_origin_point = ca->last_max_cwnd;
     221             :                 }
     222             :         }
     223             : 
     224             :         /* cubic function - calc*/
     225             :         /* calculate c * time^3 / rtt,
     226             :          *  while considering overflow in calculation of time^3
     227             :          * (so time^3 is done by using 64 bit)
     228             :          * and without the support of division of 64bit numbers
     229             :          * (so all divisions are done by using 32 bit)
     230             :          *  also NOTE the unit of those veriables
     231             :          *        time  = (t - K) / 2^bictcp_HZ
     232             :          *        c = bic_scale >> 10
     233             :          * rtt  = (srtt >> 3) / HZ
     234             :          * !!! The following code does not have overflow problems,
     235             :          * if the cwnd < 1 million packets !!!
     236             :          */
     237             : 
     238             :         /* change the unit from HZ to bictcp_HZ */
     239           2 :         t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
     240             :              << BICTCP_HZ) / HZ;
     241             : 
     242           4 :         if (t < ca->bic_K)                /* t - K */
     243           2 :                 offs = ca->bic_K - t;
     244             :         else
     245           2 :                 offs = t - ca->bic_K;
     246             : 
     247             :         /* c/rtt * (t-K)^3 */
     248           2 :         delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
     249           4 :         if (t < ca->bic_K)                                        /* below origin*/
     250           2 :                 bic_target = ca->bic_origin_point - delta;
     251             :         else                                                    /* above origin*/
     252           2 :                 bic_target = ca->bic_origin_point + delta;
     253             : 
     254             :         /* cubic function - calc bictcp_cnt*/
     255           4 :         if (bic_target > cwnd) {
     256           2 :                 ca->cnt = cwnd / (bic_target - cwnd);
     257             :         } else {
     258           2 :                 ca->cnt = 100 * cwnd;              /* very small increment*/
     259             :         }
     260             : 
     261             :         /* TCP Friendly */
     262           4 :         if (tcp_friendliness) {
     263           2 :                 u32 scale = beta_scale;
     264           2 :                 delta = (cwnd * scale) >> 3;
     265           4 :                 while (ca->ack_cnt > delta) {             /* update tcp cwnd */
     266           2 :                         ca->ack_cnt -= delta;
     267           2 :                         ca->tcp_cwnd++;
     268           1 :                 }
     269             : 
     270           2 :                 if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
     271           1 :                         delta = ca->tcp_cwnd - cwnd;
     272           1 :                         max_cnt = cwnd / delta;
     273           2 :                         if (ca->cnt > max_cnt)
     274           1 :                                 ca->cnt = max_cnt;
     275             :                 }
     276             :         }
     277             : 
     278           6 :         ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
     279           6 :         if (ca->cnt == 0)                    /* cannot be zero */
     280           3 :                 ca->cnt = 1;
     281           3 : }
     282             : 
     283             : static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
     284             : {
     285           4 :         struct tcp_sock *tp = tcp_sk(sk);
     286           4 :         struct bictcp *ca = inet_csk_ca(sk);
     287           1 : 
     288           4 :         if (!tcp_is_cwnd_limited(sk, in_flight))
     289           2 :                 return;
     290           1 : 
     291           2 :         if (tp->snd_cwnd <= tp->snd_ssthresh) {
     292           6 :                 if (hystart && after(ack, ca->end_seq))
     293           2 :                         bictcp_hystart_reset(sk);
     294           3 :                 tcp_slow_start(tp);
     295             :         } else {
     296           4 :                 bictcp_update(ca, tp->snd_cwnd);
     297           1 :                 tcp_cong_avoid_ai(tp, ca->cnt);
     298             :         }
     299           4 : 
     300             : }
     301             : 
     302             : static u32 bictcp_recalc_ssthresh(struct sock *sk)
     303             : {
     304           4 :         const struct tcp_sock *tp = tcp_sk(sk);
     305           4 :         struct bictcp *ca = inet_csk_ca(sk);
     306           1 : 
     307           2 :         ca->epoch_start = 0; /* end of epoch */
     308           1 : 
     309           1 :         /* Wmax and fast convergence */
     310           5 :         if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
     311           2 :                 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
     312             :                         / (2 * BICTCP_BETA_SCALE);
     313             :         else
     314           1 :                 ca->last_max_cwnd = tp->snd_cwnd;
     315             : 
     316           1 :         ca->loss_cwnd = tp->snd_cwnd;
     317             : 
     318           9 :         return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
     319             : }
     320             : 
     321             : static u32 bictcp_undo_cwnd(struct sock *sk)
     322             : {
     323           4 :         struct bictcp *ca = inet_csk_ca(sk);
     324           1 : 
     325          11 :         return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
     326           1 : }
     327           1 : 
     328             : static void bictcp_state(struct sock *sk, u8 new_state)
     329             : {
     330           3 :         if (new_state == TCP_CA_Loss) {
     331           4 :                 bictcp_reset(inet_csk_ca(sk));
     332           2 :                 bictcp_hystart_reset(sk);
     333             :         }
     334           2 : }
     335             : 
     336             : static void hystart_update(struct sock *sk, u32 delay)
     337             : {
     338           4 :         struct tcp_sock *tp = tcp_sk(sk);
     339           4 :         struct bictcp *ca = inet_csk_ca(sk);
     340           1 : 
     341           4 :         if (!(ca->found & hystart_detect)) {
     342           2 :                 u32 curr_jiffies = jiffies;
     343           1 : 
     344           1 :                 /* first detection parameter - ack-train detection */
     345           4 :                 if (curr_jiffies - ca->last_jiffies <= msecs_to_jiffies(2)) {
     346           2 :                         ca->last_jiffies = curr_jiffies;
     347           2 :                         if (curr_jiffies - ca->round_start >= ca->delay_min>>4)
     348           2 :                                 ca->found |= HYSTART_ACK_TRAIN;
     349             :                 }
     350             : 
     351             :                 /* obtain the minimum delay of more than sampling packets */
     352           3 :                 if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
     353           4 :                         if (ca->curr_rtt == 0 || ca->curr_rtt > delay)
     354           1 :                                 ca->curr_rtt = delay;
     355             : 
     356           2 :                         ca->sample_cnt++;
     357             :                 } else {
     358             :                         if (ca->curr_rtt > ca->delay_min +
     359          16 :                             HYSTART_DELAY_THRESH(ca->delay_min>>4))
     360           2 :                                 ca->found |= HYSTART_DELAY;
     361             :                 }
     362             :                 /*
     363             :                  * Either one of two conditions are met,
     364             :                  * we exit from slow start immediately.
     365             :                  */
     366           3 :                 if (ca->found & hystart_detect)
     367           1 :                         tp->snd_ssthresh = tp->snd_cwnd;
     368             :         }
     369           1 : }
     370             : 
     371             : /* Track delayed acknowledgment ratio using sliding window
     372             :  * ratio = (15*ratio + sample) / 16
     373             :  */
     374             : static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
     375             : {
     376           4 :         const struct inet_connection_sock *icsk = inet_csk(sk);
     377           4 :         const struct tcp_sock *tp = tcp_sk(sk);
     378           4 :         struct bictcp *ca = inet_csk_ca(sk);
     379           1 :         u32 delay;
     380           1 : 
     381           4 :         if (icsk->icsk_ca_state == TCP_CA_Open) {
     382           3 :                 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
     383           3 :                 ca->delayed_ack += cnt;
     384             :         }
     385             : 
     386             :         /* Some calls are for duplicates without timetamps */
     387           2 :         if (rtt_us < 0)
     388           1 :                 return;
     389             : 
     390             :         /* Discard delay samples right after fast recovery */
     391           2 :         if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
     392           1 :                 return;
     393             : 
     394           2 :         delay = usecs_to_jiffies(rtt_us) << 3;
     395           2 :         if (delay == 0)
     396           1 :                 delay = 1;
     397             : 
     398             :         /* first time call or link delay decreases */
     399           4 :         if (ca->delay_min == 0 || ca->delay_min > delay)
     400           1 :                 ca->delay_min = delay;
     401             : 
     402             :         /* hystart triggers when cwnd is larger than some threshold */
     403           9 :         if (hystart && tp->snd_cwnd <= tp->snd_ssthresh &&
     404             :             tp->snd_cwnd >= hystart_low_window)
     405           2 :                 hystart_update(sk, delay);
     406           2 : }
     407             : 
     408           1 : static struct tcp_congestion_ops cubictcp = {
     409             :         .init           = bictcp_init,
     410             :         .ssthresh       = bictcp_recalc_ssthresh,
     411             :         .cong_avoid     = bictcp_cong_avoid,
     412             :         .set_state      = bictcp_state,
     413             :         .undo_cwnd      = bictcp_undo_cwnd,
     414             :         .pkts_acked     = bictcp_acked,
     415             :         .owner          = THIS_MODULE,
     416             :         .name           = "cubic",
     417             : };
     418             : 
     419             : static int __init cubictcp_register(void)
     420             : {
     421           1 :         BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
     422           1 : 
     423           1 :         /* Precompute a bunch of the scaling factors that are used per-packet
     424             :          * based on SRTT of 100ms
     425             :          */
     426             : 
     427           1 :         beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
     428             : 
     429           1 :         cube_rtt_scale = (bic_scale * 10);      /* 1024*c/rtt */
     430             : 
     431             :         /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
     432             :          *  so K = cubic_root( (wmax-cwnd)*rtt/c )
     433             :          * the unit of K is bictcp_HZ=2^10, not HZ
     434             :          *
     435             :          *  c = bic_scale >> 10
     436             :          *  rtt = 100ms
     437             :          *
     438             :          * the following code has been designed and tested for
     439             :          * cwnd < 1 million packets
     440             :          * RTT < 100 seconds
     441             :          * HZ < 1,000,00  (corresponding to 10 nano-second)
     442             :          */
     443             : 
     444             :         /* 1/c * 2^2*bictcp_HZ * srtt */
     445           1 :         cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
     446             : 
     447             :         /* divide by bic_scale and by constant Srtt (100ms) */
     448           3 :         do_div(cube_factor, bic_scale * 10);
     449             : 
     450           2 :         return tcp_register_congestion_control(&cubictcp);
     451             : }
     452             : 
     453             : static void __exit cubictcp_unregister(void)
     454             : {
     455           2 :         tcp_unregister_congestion_control(&cubictcp);
     456           2 : }
     457             : 
     458             : module_init(cubictcp_register);
     459             : module_exit(cubictcp_unregister);
     460           1 : 
     461             : MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
     462             : MODULE_LICENSE("GPL");
     463             : MODULE_DESCRIPTION("CUBIC TCP");
     464             : MODULE_VERSION("2.3");

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