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/config.h>
  10 #include <linux/mm.h>
  11 #include <linux/module.h>
  12 #include <net/tcp.h>
  13
  14 #define ALPHA_BASE      (1<<7)  /* 1.0 with shift << 7 */
  15 #define BETA_MIN        (1<<6)  /* 0.5 with shift << 7 */
  16 #define BETA_MAX        102     /* 0.8 with shift << 7 */
  17
  18 static int use_rtt_scaling = 1;
  19 module_param(use_rtt_scaling, int, 0644);
  20 MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
  21
  22 static int use_bandwidth_switch = 1;
  23 module_param(use_bandwidth_switch, int, 0644);
  24 MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
  25
  26 struct htcp {
  27         u16     alpha;          /* Fixed point arith, << 7 */
  28         u8      beta;           /* Fixed point arith, << 7 */
  29         u8      modeswitch;     /* Delay modeswitch until we had at least one congestion event */
  30         u32     last_cong;      /* Time since last congestion event end */
  31         u32     undo_last_cong;
  32         u16     pkts_acked;
  33         u32     packetcount;
  34         u32     minRTT;
  35         u32     maxRTT;
  36
  37         u32     undo_maxRTT;
  38         u32     undo_old_maxB;
  39
  40         /* Bandwidth estimation */
  41         u32     minB;
  42         u32     maxB;
  43         u32     old_maxB;
  44         u32     Bi;
  45         u32     lasttime;
  46 };
  47
  48 static inline u32 htcp_cong_time(struct htcp *ca)
  49 {
  50         return jiffies - ca->last_cong;
  51 }
  52
  53 static inline u32 htcp_ccount(struct htcp *ca)
  54 {
  55         return htcp_cong_time(ca)/ca->minRTT;
  56 }
  57
  58 static inline void htcp_reset(struct htcp *ca)
  59 {
  60         ca->undo_last_cong = ca->last_cong;
  61         ca->undo_maxRTT = ca->maxRTT;
  62         ca->undo_old_maxB = ca->old_maxB;
  63
  64         ca->last_cong = jiffies;
  65 }
  66
  67 static u32 htcp_cwnd_undo(struct sock *sk)
  68 {
  69         const struct tcp_sock *tp = tcp_sk(sk);
  70         struct htcp *ca = inet_csk_ca(sk);
  71         ca->last_cong = ca->undo_last_cong;
  72         ca->maxRTT = ca->undo_maxRTT;
  73         ca->old_maxB = ca->undo_old_maxB;
  74         return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);
  75 }
  76
  77 static inline void measure_rtt(struct sock *sk)
  78 {
  79         const struct inet_connection_sock *icsk = inet_csk(sk);
  80         const struct tcp_sock *tp = tcp_sk(sk);
  81         struct htcp *ca = inet_csk_ca(sk);
  82         u32 srtt = tp->srtt>>3;
  83
  84         /* keep track of minimum RTT seen so far, minRTT is zero at first */
  85         if (ca->minRTT > srtt || !ca->minRTT)
  86                 ca->minRTT = srtt;
  87
  88         /* max RTT */
  89         if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && htcp_ccount(ca) > 3) {
  90                 if (ca->maxRTT < ca->minRTT)
  91                         ca->maxRTT = ca->minRTT;
  92                 if (ca->maxRTT < srtt && srtt <= ca->maxRTT+msecs_to_jiffies(20))
  93                         ca->maxRTT = srtt;
  94         }
  95 }
  96
  97 static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked)
  98 {
  99         const struct inet_connection_sock *icsk = inet_csk(sk);
 100         const struct tcp_sock *tp = tcp_sk(sk);
 101         struct htcp *ca = inet_csk_ca(sk);
 102         u32 now = tcp_time_stamp;
 103
 104         if (icsk->icsk_ca_state == TCP_CA_Open)
 105                 ca->pkts_acked = pkts_acked;
 106
 107         if (!use_bandwidth_switch)
 108                 return;
 109
 110         /* achieved throughput calculations */
 111         if (icsk->icsk_ca_state != TCP_CA_Open &&
 112             icsk->icsk_ca_state != TCP_CA_Disorder) {
 113                 ca->packetcount = 0;
 114                 ca->lasttime = now;
 115                 return;
 116         }
 117
 118         ca->packetcount += pkts_acked;
 119
 120         if (ca->packetcount >= tp->snd_cwnd - (ca->alpha>>7? : 1)
 121                         && now - ca->lasttime >= ca->minRTT
 122                         && ca->minRTT > 0) {
 123                 __u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);
 124                 if (htcp_ccount(ca) <= 3) {
 125                         /* just after backoff */
 126                         ca->minB = ca->maxB = ca->Bi = cur_Bi;
 127                 } else {
 128                         ca->Bi = (3*ca->Bi + cur_Bi)/4;
 129                         if (ca->Bi > ca->maxB)
 130                                 ca->maxB = ca->Bi;
 131                         if (ca->minB > ca->maxB)
 132                                 ca->minB = ca->maxB;
 133                 }
 134                 ca->packetcount = 0;
 135                 ca->lasttime = now;
 136         }
 137 }
 138
 139 static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
 140 {
 141         if (use_bandwidth_switch) {
 142                 u32 maxB = ca->maxB;
 143                 u32 old_maxB = ca->old_maxB;
 144                 ca->old_maxB = ca->maxB;
 145
 146                 if (!between(5*maxB, 4*old_maxB, 6*old_maxB)) {
 147                         ca->beta = BETA_MIN;
 148                         ca->modeswitch = 0;
 149                         return;
 150                 }
 151         }
 152
 153         if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {
 154                 ca->beta = (minRTT<<7)/maxRTT;
 155                 if (ca->beta < BETA_MIN)
 156                         ca->beta = BETA_MIN;
 157                 else if (ca->beta > BETA_MAX)
 158                         ca->beta = BETA_MAX;
 159         } else {
 160                 ca->beta = BETA_MIN;
 161                 ca->modeswitch = 1;
 162         }
 163 }
 164
 165 static inline void htcp_alpha_update(struct htcp *ca)
 166 {
 167         u32 minRTT = ca->minRTT;
 168         u32 factor = 1;
 169         u32 diff = htcp_cong_time(ca);
 170
 171         if (diff > HZ) {
 172                 diff -= HZ;
 173                 factor = 1+ ( 10*diff + ((diff/2)*(diff/2)/HZ) )/HZ;
 174         }
 175
 176         if (use_rtt_scaling && minRTT) {
 177                 u32 scale = (HZ<<3)/(10*minRTT);
 178                 scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to interval [0.5,10]<<3 */
 179                 factor = (factor<<3)/scale;
 180                 if (!factor)
 181                         factor = 1;
 182         }
 183
 184         ca->alpha = 2*factor*((1<<7)-ca->beta);
 185         if (!ca->alpha)
 186                 ca->alpha = ALPHA_BASE;
 187 }
 188
 189 /* After we have the rtt data to calculate beta, we'd still prefer to wait one
 190  * rtt before we adjust our beta to ensure we are working from a consistent
 191  * data.
 192  *
 193  * This function should be called when we hit a congestion event since only at
 194  * that point do we really have a real sense of maxRTT (the queues en route
 195  * were getting just too full now).
 196  */
 197 static void htcp_param_update(struct sock *sk)
 198 {
 199         struct htcp *ca = inet_csk_ca(sk);
 200         u32 minRTT = ca->minRTT;
 201         u32 maxRTT = ca->maxRTT;
 202
 203         htcp_beta_update(ca, minRTT, maxRTT);
 204         htcp_alpha_update(ca);
 205
 206         /* add slowly fading memory for maxRTT to accommodate routing changes etc */
 207         if (minRTT > 0 && maxRTT > minRTT)
 208                 ca->maxRTT = minRTT + ((maxRTT-minRTT)*95)/100;
 209 }
 210
 211 static u32 htcp_recalc_ssthresh(struct sock *sk)
 212 {
 213         const struct tcp_sock *tp = tcp_sk(sk);
 214         const struct htcp *ca = inet_csk_ca(sk);
 215         htcp_param_update(sk);
 216         return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
 217 }
 218
 219 static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
 220                             u32 in_flight, int data_acked)
 221 {
 222         struct tcp_sock *tp = tcp_sk(sk);
 223         struct htcp *ca = inet_csk_ca(sk);
 224
 225         if (!tcp_is_cwnd_limited(sk, in_flight))
 226                 return;
 227
 228         if (tp->snd_cwnd <= tp->snd_ssthresh)
 229                 tcp_slow_start(tp);
 230         else {
 231
 232                 measure_rtt(sk);
 233
 234                 /* In dangerous area, increase slowly.
 235                  * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
 236                  */
 237                 if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {
 238                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 239                                 tp->snd_cwnd++;
 240                         tp->snd_cwnd_cnt = 0;
 241                         htcp_alpha_update(ca);
 242                 } else
 243                         tp->snd_cwnd_cnt += ca->pkts_acked;
 244
 245                 ca->pkts_acked = 1;
 246         }
 247 }
 248
 249 /* Lower bound on congestion window. */
 250 static u32 htcp_min_cwnd(struct sock *sk)
 251 {
 252         const struct tcp_sock *tp = tcp_sk(sk);
 253         return tp->snd_ssthresh;
 254 }
 255
 256
 257 static void htcp_init(struct sock *sk)
 258 {
 259         struct htcp *ca = inet_csk_ca(sk);
 260
 261         memset(ca, 0, sizeof(struct htcp));
 262         ca->alpha = ALPHA_BASE;
 263         ca->beta = BETA_MIN;
 264         ca->pkts_acked = 1;
 265         ca->last_cong = jiffies;
 266 }
 267
 268 static void htcp_state(struct sock *sk, u8 new_state)
 269 {
 270         switch (new_state) {
 271         case TCP_CA_Open:
 272                 {
 273                         struct htcp *ca = inet_csk_ca(sk);
 274                         ca->last_cong = jiffies;
 275                 }
 276                 break;
 277         case TCP_CA_CWR:
 278         case TCP_CA_Recovery:
 279         case TCP_CA_Loss:
 280                 htcp_reset(inet_csk_ca(sk));
 281                 break;
 282         }
 283 }
 284
 285 static struct tcp_congestion_ops htcp = {
 286         .init           = htcp_init,
 287         .ssthresh       = htcp_recalc_ssthresh,
 288         .min_cwnd       = htcp_min_cwnd,
 289         .cong_avoid     = htcp_cong_avoid,
 290         .set_state      = htcp_state,
 291         .undo_cwnd      = htcp_cwnd_undo,
 292         .pkts_acked     = measure_achieved_throughput,
 293         .owner          = THIS_MODULE,
 294         .name           = "htcp",
 295 };
 296
 297 static int __init htcp_register(void)
 298 {
 299         BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
 300         BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
 301         return tcp_register_congestion_control(&htcp);
 302 }
 303
 304 static void __exit htcp_unregister(void)
 305 {
 306         tcp_unregister_congestion_control(&htcp);
 307 }
 308
 309 module_init(htcp_register);
 310 module_exit(htcp_unregister);
 311
 312 MODULE_AUTHOR("Baruch Even");
 313 MODULE_LICENSE("GPL");
 314 MODULE_DESCRIPTION("H-TCP");