net/ipv4/tcp_westwood.c

   1 /*
   2  * TCP Westwood+
   3  *
   4  *      Angelo Dell'Aera:       TCP Westwood+ support
   5  */
   6
   7 #include <linux/config.h>
   8 #include <linux/mm.h>
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <linux/inet_diag.h>
  12 #include <net/tcp.h>
  13
  14 /* TCP Westwood structure */
  15 struct westwood {
  16         u32    bw_ns_est;        /* first bandwidth estimation..not too smoothed 8) */
  17         u32    bw_est;           /* bandwidth estimate */
  18         u32    rtt_win_sx;       /* here starts a new evaluation... */
  19         u32    bk;
  20         u32    snd_una;          /* used for evaluating the number of acked bytes */
  21         u32    cumul_ack;
  22         u32    accounted;
  23         u32    rtt;
  24         u32    rtt_min;          /* minimum observed RTT */
  25 };
  26
  27
  28 /* TCP Westwood functions and constants */
  29 #define TCP_WESTWOOD_RTT_MIN   (HZ/20)  /* 50ms */
  30 #define TCP_WESTWOOD_INIT_RTT  (20*HZ)  /* maybe too conservative?! */
  31
  32 /*
  33  * @tcp_westwood_create
  34  * This function initializes fields used in TCP Westwood+,
  35  * it is called after the initial SYN, so the sequence numbers
  36  * are correct but new passive connections we have no
  37  * information about RTTmin at this time so we simply set it to
  38  * TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative
  39  * since in this way we're sure it will be updated in a consistent
  40  * way as soon as possible. It will reasonably happen within the first
  41  * RTT period of the connection lifetime.
  42  */
  43 static void tcp_westwood_init(struct sock *sk)
  44 {
  45         struct westwood *w = inet_csk_ca(sk);
  46
  47         w->bk = 0;
  48         w->bw_ns_est = 0;
  49         w->bw_est = 0;
  50         w->accounted = 0;
  51         w->cumul_ack = 0;
  52         w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
  53         w->rtt_win_sx = tcp_time_stamp;
  54         w->snd_una = tcp_sk(sk)->snd_una;
  55 }
  56
  57 /*
  58  * @westwood_do_filter
  59  * Low-pass filter. Implemented using constant coefficients.
  60  */
  61 static inline u32 westwood_do_filter(u32 a, u32 b)
  62 {
  63         return (((7 * a) + b) >> 3);
  64 }
  65
  66 static inline void westwood_filter(struct westwood *w, u32 delta)
  67 {
  68         w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
  69         w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
  70 }
  71
  72 /*
  73  * @westwood_pkts_acked
  74  * Called after processing group of packets.
  75  * but all westwood needs is the last sample of srtt.
  76  */
  77 static void tcp_westwood_pkts_acked(struct sock *sk, u32 cnt)
  78 {
  79         struct westwood *w = inet_csk_ca(sk);
  80         if (cnt > 0)
  81                 w->rtt = tcp_sk(sk)->srtt >> 3;
  82 }
  83
  84 /*
  85  * @westwood_update_window
  86  * It updates RTT evaluation window if it is the right moment to do
  87  * it. If so it calls filter for evaluating bandwidth.
  88  */
  89 static void westwood_update_window(struct sock *sk)
  90 {
  91         struct westwood *w = inet_csk_ca(sk);
  92         s32 delta = tcp_time_stamp - w->rtt_win_sx;
  93
  94         /*
  95          * See if a RTT-window has passed.
  96          * Be careful since if RTT is less than
  97          * 50ms we don't filter but we continue 'building the sample'.
  98          * This minimum limit was chosen since an estimation on small
  99          * time intervals is better to avoid...
 100          * Obviously on a LAN we reasonably will always have
 101          * right_bound = left_bound + WESTWOOD_RTT_MIN
 102          */
 103         if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {
 104                 westwood_filter(w, delta);
 105
 106                 w->bk = 0;
 107                 w->rtt_win_sx = tcp_time_stamp;
 108         }
 109 }
 110
 111 /*
 112  * @westwood_fast_bw
 113  * It is called when we are in fast path. In particular it is called when
 114  * header prediction is successful. In such case in fact update is
 115  * straight forward and doesn't need any particular care.
 116  */
 117 static inline void westwood_fast_bw(struct sock *sk)
 118 {
 119         const struct tcp_sock *tp = tcp_sk(sk);
 120         struct westwood *w = inet_csk_ca(sk);
 121
 122         westwood_update_window(sk);
 123
 124         w->bk += tp->snd_una - w->snd_una;
 125         w->snd_una = tp->snd_una;
 126         w->rtt_min = min(w->rtt, w->rtt_min);
 127 }
 128
 129 /*
 130  * @westwood_acked_count
 131  * This function evaluates cumul_ack for evaluating bk in case of
 132  * delayed or partial acks.
 133  */
 134 static inline u32 westwood_acked_count(struct sock *sk)
 135 {
 136         const struct tcp_sock *tp = tcp_sk(sk);
 137         struct westwood *w = inet_csk_ca(sk);
 138
 139         w->cumul_ack = tp->snd_una - w->snd_una;
 140
 141         /* If cumul_ack is 0 this is a dupack since it's not moving
 142          * tp->snd_una.
 143          */
 144         if (!w->cumul_ack) {
 145                 w->accounted += tp->mss_cache;
 146                 w->cumul_ack = tp->mss_cache;
 147         }
 148
 149         if (w->cumul_ack > tp->mss_cache) {
 150                 /* Partial or delayed ack */
 151                 if (w->accounted >= w->cumul_ack) {
 152                         w->accounted -= w->cumul_ack;
 153                         w->cumul_ack = tp->mss_cache;
 154                 } else {
 155                         w->cumul_ack -= w->accounted;
 156                         w->accounted = 0;
 157                 }
 158         }
 159
 160         w->snd_una = tp->snd_una;
 161
 162         return w->cumul_ack;
 163 }
 164
 165 static inline u32 westwood_bw_rttmin(const struct sock *sk)
 166 {
 167         const struct tcp_sock *tp = tcp_sk(sk);
 168         const struct westwood *w = inet_csk_ca(sk);
 169         return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
 170 }
 171
 172 /*
 173  * TCP Westwood
 174  * Here limit is evaluated as Bw estimation*RTTmin (for obtaining it
 175  * in packets we use mss_cache). Rttmin is guaranteed to be >= 2
 176  * so avoids ever returning 0.
 177  */
 178 static u32 tcp_westwood_cwnd_min(struct sock *sk)
 179 {
 180         return westwood_bw_rttmin(sk);
 181 }
 182
 183 static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
 184 {
 185         struct tcp_sock *tp = tcp_sk(sk);
 186         struct westwood *w = inet_csk_ca(sk);
 187
 188         switch(event) {
 189         case CA_EVENT_FAST_ACK:
 190                 westwood_fast_bw(sk);
 191                 break;
 192
 193         case CA_EVENT_COMPLETE_CWR:
 194                 tp->snd_cwnd = tp->snd_ssthresh = westwood_bw_rttmin(sk);
 195                 break;
 196
 197         case CA_EVENT_FRTO:
 198                 tp->snd_ssthresh = westwood_bw_rttmin(sk);
 199                 break;
 200
 201         case CA_EVENT_SLOW_ACK:
 202                 westwood_update_window(sk);
 203                 w->bk += westwood_acked_count(sk);
 204                 w->rtt_min = min(w->rtt, w->rtt_min);
 205                 break;
 206
 207         default:
 208                 /* don't care */
 209                 break;
 210         }
 211 }
 212
 213
 214 /* Extract info for Tcp socket info provided via netlink. */
 215 static void tcp_westwood_info(struct sock *sk, u32 ext,
 216                               struct sk_buff *skb)
 217 {
 218         const struct westwood *ca = inet_csk_ca(sk);
 219         if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
 220                 struct rtattr *rta;
 221                 struct tcpvegas_info *info;
 222
 223                 rta = __RTA_PUT(skb, INET_DIAG_VEGASINFO, sizeof(*info));
 224                 info = RTA_DATA(rta);
 225                 info->tcpv_enabled = 1;
 226                 info->tcpv_rttcnt = 0;
 227                 info->tcpv_rtt = jiffies_to_usecs(ca->rtt);
 228                 info->tcpv_minrtt = jiffies_to_usecs(ca->rtt_min);
 229         rtattr_failure: ;
 230         }
 231 }
 232
 233
 234 static struct tcp_congestion_ops tcp_westwood = {
 235         .init           = tcp_westwood_init,
 236         .ssthresh       = tcp_reno_ssthresh,
 237         .cong_avoid     = tcp_reno_cong_avoid,
 238         .min_cwnd       = tcp_westwood_cwnd_min,
 239         .cwnd_event     = tcp_westwood_event,
 240         .get_info       = tcp_westwood_info,
 241         .pkts_acked     = tcp_westwood_pkts_acked,
 242
 243         .owner          = THIS_MODULE,
 244         .name           = "westwood"
 245 };
 246
 247 static int __init tcp_westwood_register(void)
 248 {
 249         BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE);
 250         return tcp_register_congestion_control(&tcp_westwood);
 251 }
 252
 253 static void __exit tcp_westwood_unregister(void)
 254 {
 255         tcp_unregister_congestion_control(&tcp_westwood);
 256 }
 257
 258 module_init(tcp_westwood_register);
 259 module_exit(tcp_westwood_unregister);
 260
 261 MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera");
 262 MODULE_LICENSE("GPL");
 263 MODULE_DESCRIPTION("TCP Westwood+");