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Linux/net/ipv4/tcp_hybla.c

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  1 /*
  2  * TCP HYBLA
  3  *
  4  * TCP-HYBLA Congestion control algorithm, based on:
  5  *   C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement
  6  *   for Heterogeneous Networks",
  7  *   International Journal on satellite Communications,
  8  *                                     September 2004
  9  *    Daniele Lacamera
 10  *    root at danielinux.net
 11  */
 12 
 13 #include <linux/module.h>
 14 #include <net/tcp.h>
 15 
 16 /* Tcp Hybla structure. */
 17 struct hybla {
 18         bool  hybla_en;
 19         u32   snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
 20         u32   rho;            /* Rho parameter, integer part  */
 21         u32   rho2;           /* Rho * Rho, integer part */
 22         u32   rho_3ls;        /* Rho parameter, <<3 */
 23         u32   rho2_7ls;       /* Rho^2, <<7     */
 24         u32   minrtt_us;      /* Minimum smoothed round trip time value seen */
 25 };
 26 
 27 /* Hybla reference round trip time (default= 1/40 sec = 25 ms), in ms */
 28 static int rtt0 = 25;
 29 module_param(rtt0, int, 0644);
 30 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
 31 
 32 /* This is called to refresh values for hybla parameters */
 33 static inline void hybla_recalc_param (struct sock *sk)
 34 {
 35         struct hybla *ca = inet_csk_ca(sk);
 36 
 37         ca->rho_3ls = max_t(u32,
 38                             tcp_sk(sk)->srtt_us / (rtt0 * USEC_PER_MSEC),
 39                             8U);
 40         ca->rho = ca->rho_3ls >> 3;
 41         ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
 42         ca->rho2 = ca->rho2_7ls >> 7;
 43 }
 44 
 45 static void hybla_init(struct sock *sk)
 46 {
 47         struct tcp_sock *tp = tcp_sk(sk);
 48         struct hybla *ca = inet_csk_ca(sk);
 49 
 50         ca->rho = 0;
 51         ca->rho2 = 0;
 52         ca->rho_3ls = 0;
 53         ca->rho2_7ls = 0;
 54         ca->snd_cwnd_cents = 0;
 55         ca->hybla_en = true;
 56         tp->snd_cwnd = 2;
 57         tp->snd_cwnd_clamp = 65535;
 58 
 59         /* 1st Rho measurement based on initial srtt */
 60         hybla_recalc_param(sk);
 61 
 62         /* set minimum rtt as this is the 1st ever seen */
 63         ca->minrtt_us = tp->srtt_us;
 64         tp->snd_cwnd = ca->rho;
 65 }
 66 
 67 static void hybla_state(struct sock *sk, u8 ca_state)
 68 {
 69         struct hybla *ca = inet_csk_ca(sk);
 70 
 71         ca->hybla_en = (ca_state == TCP_CA_Open);
 72 }
 73 
 74 static inline u32 hybla_fraction(u32 odds)
 75 {
 76         static const u32 fractions[] = {
 77                 128, 139, 152, 165, 181, 197, 215, 234,
 78         };
 79 
 80         return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
 81 }
 82 
 83 /* TCP Hybla main routine.
 84  * This is the algorithm behavior:
 85  *     o Recalc Hybla parameters if min_rtt has changed
 86  *     o Give cwnd a new value based on the model proposed
 87  *     o remember increments <1
 88  */
 89 static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 90 {
 91         struct tcp_sock *tp = tcp_sk(sk);
 92         struct hybla *ca = inet_csk_ca(sk);
 93         u32 increment, odd, rho_fractions;
 94         int is_slowstart = 0;
 95 
 96         /*  Recalculate rho only if this srtt is the lowest */
 97         if (tp->srtt_us < ca->minrtt_us) {
 98                 hybla_recalc_param(sk);
 99                 ca->minrtt_us = tp->srtt_us;
100         }
101 
102         if (!tcp_is_cwnd_limited(sk))
103                 return;
104 
105         if (!ca->hybla_en) {
106                 tcp_reno_cong_avoid(sk, ack, acked);
107                 return;
108         }
109 
110         if (ca->rho == 0)
111                 hybla_recalc_param(sk);
112 
113         rho_fractions = ca->rho_3ls - (ca->rho << 3);
114 
115         if (tcp_in_slow_start(tp)) {
116                 /*
117                  * slow start
118                  *      INC = 2^RHO - 1
119                  * This is done by splitting the rho parameter
120                  * into 2 parts: an integer part and a fraction part.
121                  * Inrement<<7 is estimated by doing:
122                  *             [2^(int+fract)]<<7
123                  * that is equal to:
124                  *             (2^int)  *  [(2^fract) <<7]
125                  * 2^int is straightly computed as 1<<int,
126                  * while we will use hybla_slowstart_fraction_increment() to
127                  * calculate 2^fract in a <<7 value.
128                  */
129                 is_slowstart = 1;
130                 increment = ((1 << min(ca->rho, 16U)) *
131                         hybla_fraction(rho_fractions)) - 128;
132         } else {
133                 /*
134                  * congestion avoidance
135                  * INC = RHO^2 / W
136                  * as long as increment is estimated as (rho<<7)/window
137                  * it already is <<7 and we can easily count its fractions.
138                  */
139                 increment = ca->rho2_7ls / tp->snd_cwnd;
140                 if (increment < 128)
141                         tp->snd_cwnd_cnt++;
142         }
143 
144         odd = increment % 128;
145         tp->snd_cwnd += increment >> 7;
146         ca->snd_cwnd_cents += odd;
147 
148         /* check when fractions goes >=128 and increase cwnd by 1. */
149         while (ca->snd_cwnd_cents >= 128) {
150                 tp->snd_cwnd++;
151                 ca->snd_cwnd_cents -= 128;
152                 tp->snd_cwnd_cnt = 0;
153         }
154         /* check when cwnd has not been incremented for a while */
155         if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) {
156                 tp->snd_cwnd++;
157                 tp->snd_cwnd_cnt = 0;
158         }
159         /* clamp down slowstart cwnd to ssthresh value. */
160         if (is_slowstart)
161                 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
162 
163         tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
164 }
165 
166 static struct tcp_congestion_ops tcp_hybla __read_mostly = {
167         .init           = hybla_init,
168         .ssthresh       = tcp_reno_ssthresh,
169         .cong_avoid     = hybla_cong_avoid,
170         .set_state      = hybla_state,
171 
172         .owner          = THIS_MODULE,
173         .name           = "hybla"
174 };
175 
176 static int __init hybla_register(void)
177 {
178         BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
179         return tcp_register_congestion_control(&tcp_hybla);
180 }
181 
182 static void __exit hybla_unregister(void)
183 {
184         tcp_unregister_congestion_control(&tcp_hybla);
185 }
186 
187 module_init(hybla_register);
188 module_exit(hybla_unregister);
189 
190 MODULE_AUTHOR("Daniele Lacamera");
191 MODULE_LICENSE("GPL");
192 MODULE_DESCRIPTION("TCP Hybla");
193 

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