net/ipv4/tcp_htcp.c

   1 /*
   2  * H-TCP congestion control. The algorithm is detailed in:
   3  * R.N.Shorten, D.J.Leith:
   4  *   "H-TCP: TCP for high-speed and long-distance networks"
   5  *   Proc. PFLDnet, Argonne, 2004.
   6  * http://www.hamilton.ie/net/htcp3.pdf
   7  */
   8
   9 #include <linux/mm.h>
  10 #include <linux/module.h>
  11 #include <net/tcp.h>
  12
  13 #define ALPHA_BASE      (1<<7)  /* 1.0 with shift << 7 */
  14 #define BETA_MIN        (1<<6)  /* 0.5 with shift << 7 */
  15 #define BETA_MAX        102     /* 0.8 with shift << 7 */
  16
  17 static int use_rtt_scaling = 1;
  18 module_param(use_rtt_scaling, int, 0644);
  19 MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
  20
  21 static int use_bandwidth_switch = 1;
  22 module_param(use_bandwidth_switch, int, 0644);
  23 MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
  24
  25 struct htcp {
  26         u16     alpha;          /* Fixed point arith, << 7 */
  27         u8      beta;           /* Fixed point arith, << 7 */
  28         u8      modeswitch;     /* Delay modeswitch until we had at least one congestion event */
  29         u32     last_cong;      /* Time since last congestion event end */
  30         u32     undo_last_cong;
  31         u16     pkts_acked;
  32         u32     packetcount;
  33         u32     minRTT;
  34         u32     maxRTT;
  35
  36         u32     undo_maxRTT;
  37         u32     undo_old_maxB;
  38
  39         /* Bandwidth estimation */
  40         u32     minB;
  41         u32     maxB;
  42         u32     old_maxB;
  43         u32     Bi;
  44         u32     lasttime;
  45 };
  46
  47 static inline u32 htcp_cong_time(struct htcp *ca)
  48 {
  49         return jiffies - ca->last_cong;
  50 }
  51
  52 static inline u32 htcp_ccount(struct htcp *ca)
  53 {
  54         return htcp_cong_time(ca)/ca->minRTT;
  55 }
  56
  57 static inline void htcp_reset(struct htcp *ca)
  58 {
  59         ca->undo_last_cong = ca->last_cong;
  60         ca->undo_maxRTT = ca->maxRTT;
  61         ca->undo_old_maxB = ca->old_maxB;
  62
  63         ca->last_cong = jiffies;
  64 }
  65
  66 static u32 htcp_cwnd_undo(struct sock *sk)
  67 {
  68         const struct tcp_sock *tp = tcp_sk(sk);
  69         struct htcp *ca = inet_csk_ca(sk);
  70         ca->last_cong = ca->undo_last_cong;
  71         ca->maxRTT = ca->undo_maxRTT;
  72         ca->old_maxB = ca->undo_old_maxB;
  73         return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);
  74 }
  75
  76 static inline void measure_rtt(struct sock *sk)
  77 {
  78         const struct inet_connection_sock *icsk = inet_csk(sk);
  79         const struct tcp_sock *tp = tcp_sk(sk);
  80         struct htcp *ca = inet_csk_ca(sk);
  81         u32 srtt = tp->srtt>>3;
  82
  83         /* keep track of minimum RTT seen so far, minRTT is zero at first */
  84         if (ca->minRTT > srtt || !ca->minRTT)
  85                 ca->minRTT = srtt;
  86
  87         /* max RTT */
  88         if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && htcp_ccount(ca) > 3) {
  89                 if (ca->maxRTT < ca->minRTT)
  90                         ca->maxRTT = ca->minRTT;
  91                 if (ca->maxRTT < srtt && srtt <= ca->maxRTT+msecs_to_jiffies(20))
  92                         ca->maxRTT = srtt;
  93         }
  94 }
  95
  96 static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked)
  97 {
  98         const struct inet_connection_sock *icsk = inet_csk(sk);
  99         const struct tcp_sock *tp = tcp_sk(sk);
 100         struct htcp *ca = inet_csk_ca(sk);
 101         u32 now = tcp_time_stamp;
 102
 103         if (icsk->icsk_ca_state == TCP_CA_Open)
 104                 ca->pkts_acked = pkts_acked;
 105
 106         if (!use_bandwidth_switch)
 107                 return;
 108
 109         /* achieved throughput calculations */
 110         if (icsk->icsk_ca_state != TCP_CA_Open &&
 111             icsk->icsk_ca_state != TCP_CA_Disorder) {
 112                 ca->packetcount = 0;
 113                 ca->lasttime = now;
 114                 return;
 115         }
 116
 117         ca->packetcount += pkts_acked;
 118
 119         if (ca->packetcount >= tp->snd_cwnd - (ca->alpha>>7? : 1)
 120                         && now - ca->lasttime >= ca->minRTT
 121                         && ca->minRTT > 0) {
 122                 __u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);
 123                 if (htcp_ccount(ca) <= 3) {
 124                         /* just after backoff */
 125                         ca->minB = ca->maxB = ca->Bi = cur_Bi;
 126                 } else {
 127                         ca->Bi = (3*ca->Bi + cur_Bi)/4;
 128                         if (ca->Bi > ca->maxB)
 129                                 ca->maxB = ca->Bi;
 130                         if (ca->minB > ca->maxB)
 131                                 ca->minB = ca->maxB;
 132                 }
 133                 ca->packetcount = 0;
 134                 ca->lasttime = now;
 135         }
 136 }
 137
 138 static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
 139 {
 140         if (use_bandwidth_switch) {
 141                 u32 maxB = ca->maxB;
 142                 u32 old_maxB = ca->old_maxB;
 143                 ca->old_maxB = ca->maxB;
 144
 145                 if (!between(5*maxB, 4*old_maxB, 6*old_maxB)) {
 146                         ca->beta = BETA_MIN;
 147                         ca->modeswitch = 0;
 148                         return;
 149                 }
 150         }
 151
 152         if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {
 153                 ca->beta = (minRTT<<7)/maxRTT;
 154                 if (ca->beta < BETA_MIN)
 155                         ca->beta = BETA_MIN;
 156                 else if (ca->beta > BETA_MAX)
 157                         ca->beta = BETA_MAX;
 158         } else {
 159                 ca->beta = BETA_MIN;
 160                 ca->modeswitch = 1;
 161         }
 162 }
 163
 164 static inline void htcp_alpha_update(struct htcp *ca)
 165 {
 166         u32 minRTT = ca->minRTT;
 167         u32 factor = 1;
 168         u32 diff = htcp_cong_time(ca);
 169
 170         if (diff > HZ) {
 171                 diff -= HZ;
 172                 factor = 1+ ( 10*diff + ((diff/2)*(diff/2)/HZ) )/HZ;
 173         }
 174
 175         if (use_rtt_scaling && minRTT) {
 176                 u32 scale = (HZ<<3)/(10*minRTT);
 177                 scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to interval [0.5,10]<<3 */
 178                 factor = (factor<<3)/scale;
 179                 if (!factor)
 180                         factor = 1;
 181         }
 182
 183         ca->alpha = 2*factor*((1<<7)-ca->beta);
 184         if (!ca->alpha)
 185                 ca->alpha = ALPHA_BASE;
 186 }
 187
 188 /* After we have the rtt data to calculate beta, we'd still prefer to wait one
 189  * rtt before we adjust our beta to ensure we are working from a consistent
 190  * data.
 191  *
 192  * This function should be called when we hit a congestion event since only at
 193  * that point do we really have a real sense of maxRTT (the queues en route
 194  * were getting just too full now).
 195  */
 196 static void htcp_param_update(struct sock *sk)
 197 {
 198         struct htcp *ca = inet_csk_ca(sk);
 199         u32 minRTT = ca->minRTT;
 200         u32 maxRTT = ca->maxRTT;
 201
 202         htcp_beta_update(ca, minRTT, maxRTT);
 203         htcp_alpha_update(ca);
 204
 205         /* add slowly fading memory for maxRTT to accommodate routing changes etc */
 206         if (minRTT > 0 && maxRTT > minRTT)
 207                 ca->maxRTT = minRTT + ((maxRTT-minRTT)*95)/100;
 208 }
 209
 210 static u32 htcp_recalc_ssthresh(struct sock *sk)
 211 {
 212         const struct tcp_sock *tp = tcp_sk(sk);
 213         const struct htcp *ca = inet_csk_ca(sk);
 214         htcp_param_update(sk);
 215         return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
 216 }
 217
 218 static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 219                             u32 in_flight, int data_acked)
 220 {
 221         struct tcp_sock *tp = tcp_sk(sk);
 222         struct htcp *ca = inet_csk_ca(sk);
 223
 224         if (!tcp_is_cwnd_limited(sk, in_flight))
 225                 return;
 226
 227         if (tp->snd_cwnd <= tp->snd_ssthresh)
 228                 tcp_slow_start(tp);
 229         else {
 230
 231                 measure_rtt(sk);
 232
 233                 /* In dangerous area, increase slowly.
 234                  * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
 235                  */
 236                 if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {
 237                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 238                                 tp->snd_cwnd++;
 239                         tp->snd_cwnd_cnt = 0;
 240                         htcp_alpha_update(ca);
 241                 } else
 242                         tp->snd_cwnd_cnt += ca->pkts_acked;
 243
 244                 ca->pkts_acked = 1;
 245         }
 246 }
 247
 248 static void htcp_init(struct sock *sk)
 249 {
 250         struct htcp *ca = inet_csk_ca(sk);
 251
 252         memset(ca, 0, sizeof(struct htcp));
 253         ca->alpha = ALPHA_BASE;
 254         ca->beta = BETA_MIN;
 255         ca->pkts_acked = 1;
 256         ca->last_cong = jiffies;
 257 }
 258
 259 static void htcp_state(struct sock *sk, u8 new_state)
 260 {
 261         switch (new_state) {
 262         case TCP_CA_Open:
 263                 {
 264                         struct htcp *ca = inet_csk_ca(sk);
 265                         ca->last_cong = jiffies;
 266                 }
 267                 break;
 268         case TCP_CA_CWR:
 269         case TCP_CA_Recovery:
 270         case TCP_CA_Loss:
 271                 htcp_reset(inet_csk_ca(sk));
 272                 break;
 273         }
 274 }
 275
 276 static struct tcp_congestion_ops htcp = {
 277         .init           = htcp_init,
 278         .ssthresh       = htcp_recalc_ssthresh,
 279         .cong_avoid     = htcp_cong_avoid,
 280         .set_state      = htcp_state,
 281         .undo_cwnd      = htcp_cwnd_undo,
 282         .pkts_acked     = measure_achieved_throughput,
 283         .owner          = THIS_MODULE,
 284         .name           = "htcp",
 285 };
 286
 287 static int __init htcp_register(void)
 288 {
 289         BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
 290         BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
 291         return tcp_register_congestion_control(&htcp);
 292 }
 293
 294 static void __exit htcp_unregister(void)
 295 {
 296         tcp_unregister_congestion_control(&htcp);
 297 }
 298
 299 module_init(htcp_register);
 300 module_exit(htcp_unregister);
 301
 302 MODULE_AUTHOR("Baruch Even");
 303 MODULE_LICENSE("GPL");
 304 MODULE_DESCRIPTION("H-TCP");