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Linux/net/ipv4/tcp_veno.c

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  1 /*
  2  * TCP Veno congestion control
  3  *
  4  * This is based on the congestion detection/avoidance scheme described in
  5  *    C. P. Fu, S. C. Liew.
  6  *    "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
  7  *    IEEE Journal on Selected Areas in Communication,
  8  *    Feb. 2003.
  9  *      See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
 10  */
 11 
 12 #include <linux/mm.h>
 13 #include <linux/module.h>
 14 #include <linux/skbuff.h>
 15 #include <linux/inet_diag.h>
 16 
 17 #include <net/tcp.h>
 18 
 19 /* Default values of the Veno variables, in fixed-point representation
 20  * with V_PARAM_SHIFT bits to the right of the binary point.
 21  */
 22 #define V_PARAM_SHIFT 1
 23 static const int beta = 3 << V_PARAM_SHIFT;
 24 
 25 /* Veno variables */
 26 struct veno {
 27         u8 doing_veno_now;      /* if true, do veno for this rtt */
 28         u16 cntrtt;             /* # of rtts measured within last rtt */
 29         u32 minrtt;             /* min of rtts measured within last rtt (in usec) */
 30         u32 basertt;            /* the min of all Veno rtt measurements seen (in usec) */
 31         u32 inc;                /* decide whether to increase cwnd */
 32         u32 diff;               /* calculate the diff rate */
 33 };
 34 
 35 /* There are several situations when we must "re-start" Veno:
 36  *
 37  *  o when a connection is established
 38  *  o after an RTO
 39  *  o after fast recovery
 40  *  o when we send a packet and there is no outstanding
 41  *    unacknowledged data (restarting an idle connection)
 42  *
 43  */
 44 static inline void veno_enable(struct sock *sk)
 45 {
 46         struct veno *veno = inet_csk_ca(sk);
 47 
 48         /* turn on Veno */
 49         veno->doing_veno_now = 1;
 50 
 51         veno->minrtt = 0x7fffffff;
 52 }
 53 
 54 static inline void veno_disable(struct sock *sk)
 55 {
 56         struct veno *veno = inet_csk_ca(sk);
 57 
 58         /* turn off Veno */
 59         veno->doing_veno_now = 0;
 60 }
 61 
 62 static void tcp_veno_init(struct sock *sk)
 63 {
 64         struct veno *veno = inet_csk_ca(sk);
 65 
 66         veno->basertt = 0x7fffffff;
 67         veno->inc = 1;
 68         veno_enable(sk);
 69 }
 70 
 71 /* Do rtt sampling needed for Veno. */
 72 static void tcp_veno_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
 73 {
 74         struct veno *veno = inet_csk_ca(sk);
 75         u32 vrtt;
 76 
 77         if (rtt_us < 0)
 78                 return;
 79 
 80         /* Never allow zero rtt or baseRTT */
 81         vrtt = rtt_us + 1;
 82 
 83         /* Filter to find propagation delay: */
 84         if (vrtt < veno->basertt)
 85                 veno->basertt = vrtt;
 86 
 87         /* Find the min rtt during the last rtt to find
 88          * the current prop. delay + queuing delay:
 89          */
 90         veno->minrtt = min(veno->minrtt, vrtt);
 91         veno->cntrtt++;
 92 }
 93 
 94 static void tcp_veno_state(struct sock *sk, u8 ca_state)
 95 {
 96         if (ca_state == TCP_CA_Open)
 97                 veno_enable(sk);
 98         else
 99                 veno_disable(sk);
100 }
101 
102 /*
103  * If the connection is idle and we are restarting,
104  * then we don't want to do any Veno calculations
105  * until we get fresh rtt samples.  So when we
106  * restart, we reset our Veno state to a clean
107  * state. After we get acks for this flight of
108  * packets, _then_ we can make Veno calculations
109  * again.
110  */
111 static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
112 {
113         if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
114                 tcp_veno_init(sk);
115 }
116 
117 static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
118 {
119         struct tcp_sock *tp = tcp_sk(sk);
120         struct veno *veno = inet_csk_ca(sk);
121 
122         if (!veno->doing_veno_now) {
123                 tcp_reno_cong_avoid(sk, ack, acked);
124                 return;
125         }
126 
127         /* limited by applications */
128         if (!tcp_is_cwnd_limited(sk))
129                 return;
130 
131         /* We do the Veno calculations only if we got enough rtt samples */
132         if (veno->cntrtt <= 2) {
133                 /* We don't have enough rtt samples to do the Veno
134                  * calculation, so we'll behave like Reno.
135                  */
136                 tcp_reno_cong_avoid(sk, ack, acked);
137         } else {
138                 u64 target_cwnd;
139                 u32 rtt;
140 
141                 /* We have enough rtt samples, so, using the Veno
142                  * algorithm, we determine the state of the network.
143                  */
144 
145                 rtt = veno->minrtt;
146 
147                 target_cwnd = (u64)tp->snd_cwnd * veno->basertt;
148                 target_cwnd <<= V_PARAM_SHIFT;
149                 do_div(target_cwnd, rtt);
150 
151                 veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
152 
153                 if (tp->snd_cwnd <= tp->snd_ssthresh) {
154                         /* Slow start.  */
155                         tcp_slow_start(tp, acked);
156                 } else {
157                         /* Congestion avoidance. */
158                         if (veno->diff < beta) {
159                                 /* In the "non-congestive state", increase cwnd
160                                  *  every rtt.
161                                  */
162                                 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1);
163                         } else {
164                                 /* In the "congestive state", increase cwnd
165                                  * every other rtt.
166                                  */
167                                 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
168                                         if (veno->inc &&
169                                             tp->snd_cwnd < tp->snd_cwnd_clamp) {
170                                                 tp->snd_cwnd++;
171                                                 veno->inc = 0;
172                                         } else
173                                                 veno->inc = 1;
174                                         tp->snd_cwnd_cnt = 0;
175                                 } else
176                                         tp->snd_cwnd_cnt++;
177                         }
178                 }
179                 if (tp->snd_cwnd < 2)
180                         tp->snd_cwnd = 2;
181                 else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
182                         tp->snd_cwnd = tp->snd_cwnd_clamp;
183         }
184         /* Wipe the slate clean for the next rtt. */
185         /* veno->cntrtt = 0; */
186         veno->minrtt = 0x7fffffff;
187 }
188 
189 /* Veno MD phase */
190 static u32 tcp_veno_ssthresh(struct sock *sk)
191 {
192         const struct tcp_sock *tp = tcp_sk(sk);
193         struct veno *veno = inet_csk_ca(sk);
194 
195         if (veno->diff < beta)
196                 /* in "non-congestive state", cut cwnd by 1/5 */
197                 return max(tp->snd_cwnd * 4 / 5, 2U);
198         else
199                 /* in "congestive state", cut cwnd by 1/2 */
200                 return max(tp->snd_cwnd >> 1U, 2U);
201 }
202 
203 static struct tcp_congestion_ops tcp_veno __read_mostly = {
204         .init           = tcp_veno_init,
205         .ssthresh       = tcp_veno_ssthresh,
206         .cong_avoid     = tcp_veno_cong_avoid,
207         .pkts_acked     = tcp_veno_pkts_acked,
208         .set_state      = tcp_veno_state,
209         .cwnd_event     = tcp_veno_cwnd_event,
210 
211         .owner          = THIS_MODULE,
212         .name           = "veno",
213 };
214 
215 static int __init tcp_veno_register(void)
216 {
217         BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
218         tcp_register_congestion_control(&tcp_veno);
219         return 0;
220 }
221 
222 static void __exit tcp_veno_unregister(void)
223 {
224         tcp_unregister_congestion_control(&tcp_veno);
225 }
226 
227 module_init(tcp_veno_register);
228 module_exit(tcp_veno_unregister);
229 
230 MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
231 MODULE_LICENSE("GPL");
232 MODULE_DESCRIPTION("TCP Veno");
233 

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