[TCP] BIC: spelling and whitespace
[linux-2.6.git] / net / ipv4 / tcp_bic.c
1 /*
2  * Binary Increase Congestion control for TCP
3  *
4  * This is from the implementation of BICTCP in
5  * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
6  *  "Binary Increase Congestion Control for Fast, Long Distance
7  *  Networks" in InfoComm 2004
8  * Available from:
9  *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
10  *
11  * Unless BIC is enabled and congestion window is large
12  * this behaves the same as the original Reno.
13  */
14
15 #include <linux/config.h>
16 #include <linux/mm.h>
17 #include <linux/module.h>
18 #include <net/tcp.h>
19
20
21 #define BICTCP_BETA_SCALE    1024       /* Scale factor beta calculation
22                                          * max_cwnd = snd_cwnd * beta
23                                          */
24 #define BICTCP_B                4        /*
25                                           * In binary search,
26                                           * go to point (max+min)/N
27                                           */
28
29 static int fast_convergence = 1;
30 static int max_increment = 16;
31 static int low_window = 14;
32 static int beta = 819;          /* = 819/1024 (BICTCP_BETA_SCALE) */
33 static int initial_ssthresh = 100;
34 static int smooth_part = 20;
35
36 module_param(fast_convergence, int, 0644);
37 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
38 module_param(max_increment, int, 0644);
39 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
40 module_param(low_window, int, 0644);
41 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
42 module_param(beta, int, 0644);
43 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
44 module_param(initial_ssthresh, int, 0644);
45 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
46 module_param(smooth_part, int, 0644);
47 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
48
49
50 /* BIC TCP Parameters */
51 struct bictcp {
52         u32     cnt;            /* increase cwnd by 1 after ACKs */
53         u32     last_max_cwnd;  /* last maximum snd_cwnd */
54         u32     loss_cwnd;      /* congestion window at last loss */
55         u32     last_cwnd;      /* the last snd_cwnd */
56         u32     last_time;      /* time when updated last_cwnd */
57         u32     epoch_start;    /* beginning of an epoch */
58 #define ACK_RATIO_SHIFT 4
59         u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
60 };
61
62 static inline void bictcp_reset(struct bictcp *ca)
63 {
64         ca->cnt = 0;
65         ca->last_max_cwnd = 0;
66         ca->loss_cwnd = 0;
67         ca->last_cwnd = 0;
68         ca->last_time = 0;
69         ca->epoch_start = 0;
70         ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
71 }
72
73 static void bictcp_init(struct sock *sk)
74 {
75         bictcp_reset(inet_csk_ca(sk));
76         if (initial_ssthresh)
77                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
78 }
79
80 /*
81  * Compute congestion window to use.
82  */
83 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
84 {
85         if (ca->last_cwnd == cwnd &&
86             (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
87                 return;
88
89         ca->last_cwnd = cwnd;
90         ca->last_time = tcp_time_stamp;
91
92         if (ca->epoch_start == 0) /* record the beginning of an epoch */
93                 ca->epoch_start = tcp_time_stamp;
94
95         /* start off normal */
96         if (cwnd <= low_window) {
97                 ca->cnt = cwnd;
98                 return;
99         }
100
101         /* binary increase */
102         if (cwnd < ca->last_max_cwnd) {
103                 __u32   dist = (ca->last_max_cwnd - cwnd)
104                         / BICTCP_B;
105
106                 if (dist > max_increment)
107                         /* linear increase */
108                         ca->cnt = cwnd / max_increment;
109                 else if (dist <= 1U)
110                         /* binary search increase */
111                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
112                 else
113                         /* binary search increase */
114                         ca->cnt = cwnd / dist;
115         } else {
116                 /* slow start AMD linear increase */
117                 if (cwnd < ca->last_max_cwnd + BICTCP_B)
118                         /* slow start */
119                         ca->cnt = (cwnd * smooth_part) / BICTCP_B;
120                 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
121                         /* slow start */
122                         ca->cnt = (cwnd * (BICTCP_B-1))
123                                 / (cwnd - ca->last_max_cwnd);
124                 else
125                         /* linear increase */
126                         ca->cnt = cwnd / max_increment;
127         }
128
129         /* if in slow start or link utilization is very low */
130         if (ca->loss_cwnd == 0) {
131                 if (ca->cnt > 20) /* increase cwnd 5% per RTT */
132                         ca->cnt = 20;
133         }
134
135         ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
136         if (ca->cnt == 0)                       /* cannot be zero */
137                 ca->cnt = 1;
138 }
139
140 static void bictcp_cong_avoid(struct sock *sk, u32 ack,
141                               u32 seq_rtt, u32 in_flight, int data_acked)
142 {
143         struct tcp_sock *tp = tcp_sk(sk);
144         struct bictcp *ca = inet_csk_ca(sk);
145
146         if (!tcp_is_cwnd_limited(sk, in_flight))
147                 return;
148
149         if (tp->snd_cwnd <= tp->snd_ssthresh)
150                 tcp_slow_start(tp);
151         else {
152                 bictcp_update(ca, tp->snd_cwnd);
153
154                 /* In dangerous area, increase slowly.
155                  * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
156                  */
157                 if (tp->snd_cwnd_cnt >= ca->cnt) {
158                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
159                                 tp->snd_cwnd++;
160                         tp->snd_cwnd_cnt = 0;
161                 } else
162                         tp->snd_cwnd_cnt++;
163         }
164
165 }
166
167 /*
168  *      behave like Reno until low_window is reached,
169  *      then increase congestion window slowly
170  */
171 static u32 bictcp_recalc_ssthresh(struct sock *sk)
172 {
173         const struct tcp_sock *tp = tcp_sk(sk);
174         struct bictcp *ca = inet_csk_ca(sk);
175
176         ca->epoch_start = 0;    /* end of epoch */
177
178         /* Wmax and fast convergence */
179         if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
180                 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
181                         / (2 * BICTCP_BETA_SCALE);
182         else
183                 ca->last_max_cwnd = tp->snd_cwnd;
184
185         ca->loss_cwnd = tp->snd_cwnd;
186
187
188         if (tp->snd_cwnd <= low_window)
189                 return max(tp->snd_cwnd >> 1U, 2U);
190         else
191                 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
192 }
193
194 static u32 bictcp_undo_cwnd(struct sock *sk)
195 {
196         const struct tcp_sock *tp = tcp_sk(sk);
197         const struct bictcp *ca = inet_csk_ca(sk);
198         return max(tp->snd_cwnd, ca->last_max_cwnd);
199 }
200
201 static u32 bictcp_min_cwnd(struct sock *sk)
202 {
203         const struct tcp_sock *tp = tcp_sk(sk);
204         return tp->snd_ssthresh;
205 }
206
207 static void bictcp_state(struct sock *sk, u8 new_state)
208 {
209         if (new_state == TCP_CA_Loss)
210                 bictcp_reset(inet_csk_ca(sk));
211 }
212
213 /* Track delayed acknowledgment ratio using sliding window
214  * ratio = (15*ratio + sample) / 16
215  */
216 static void bictcp_acked(struct sock *sk, u32 cnt)
217 {
218         const struct inet_connection_sock *icsk = inet_csk(sk);
219
220         if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
221                 struct bictcp *ca = inet_csk_ca(sk);
222                 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
223                 ca->delayed_ack += cnt;
224         }
225 }
226
227
228 static struct tcp_congestion_ops bictcp = {
229         .init           = bictcp_init,
230         .ssthresh       = bictcp_recalc_ssthresh,
231         .cong_avoid     = bictcp_cong_avoid,
232         .set_state      = bictcp_state,
233         .undo_cwnd      = bictcp_undo_cwnd,
234         .min_cwnd       = bictcp_min_cwnd,
235         .pkts_acked     = bictcp_acked,
236         .owner          = THIS_MODULE,
237         .name           = "bic",
238 };
239
240 static int __init bictcp_register(void)
241 {
242         BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
243         return tcp_register_congestion_control(&bictcp);
244 }
245
246 static void __exit bictcp_unregister(void)
247 {
248         tcp_unregister_congestion_control(&bictcp);
249 }
250
251 module_init(bictcp_register);
252 module_exit(bictcp_unregister);
253
254 MODULE_AUTHOR("Stephen Hemminger");
255 MODULE_LICENSE("GPL");
256 MODULE_DESCRIPTION("BIC TCP");