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Linux/net/ipv4/tcp_yeah.c

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  1 /*
  2  *
  3  *   YeAH TCP
  4  *
  5  * For further details look at:
  6  *    http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
  7  *
  8  */
  9 #include <linux/mm.h>
 10 #include <linux/module.h>
 11 #include <linux/skbuff.h>
 12 #include <linux/inet_diag.h>
 13 
 14 #include <net/tcp.h>
 15 
 16 #include "tcp_vegas.h"
 17 
 18 #define TCP_YEAH_ALPHA       80 //lin number of packets queued at the bottleneck
 19 #define TCP_YEAH_GAMMA        1 //lin fraction of queue to be removed per rtt
 20 #define TCP_YEAH_DELTA        3 //log minimum fraction of cwnd to be removed on loss
 21 #define TCP_YEAH_EPSILON      1 //log maximum fraction to be removed on early decongestion
 22 #define TCP_YEAH_PHY          8 //lin maximum delta from base
 23 #define TCP_YEAH_RHO         16 //lin minimum number of consecutive rtt to consider competition on loss
 24 #define TCP_YEAH_ZETA        50 //lin minimum number of state switchs to reset reno_count
 25 
 26 #define TCP_SCALABLE_AI_CNT      100U
 27 
 28 /* YeAH variables */
 29 struct yeah {
 30         struct vegas vegas;     /* must be first */
 31 
 32         /* YeAH */
 33         u32 lastQ;
 34         u32 doing_reno_now;
 35 
 36         u32 reno_count;
 37         u32 fast_count;
 38 
 39         u32 pkts_acked;
 40 };
 41 
 42 static void tcp_yeah_init(struct sock *sk)
 43 {
 44         struct tcp_sock *tp = tcp_sk(sk);
 45         struct yeah *yeah = inet_csk_ca(sk);
 46 
 47         tcp_vegas_init(sk);
 48 
 49         yeah->doing_reno_now = 0;
 50         yeah->lastQ = 0;
 51 
 52         yeah->reno_count = 2;
 53 
 54         /* Ensure the MD arithmetic works.  This is somewhat pedantic,
 55          * since I don't think we will see a cwnd this large. :) */
 56         tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
 57 
 58 }
 59 
 60 
 61 static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked, s32 rtt_us)
 62 {
 63         const struct inet_connection_sock *icsk = inet_csk(sk);
 64         struct yeah *yeah = inet_csk_ca(sk);
 65 
 66         if (icsk->icsk_ca_state == TCP_CA_Open)
 67                 yeah->pkts_acked = pkts_acked;
 68 
 69         tcp_vegas_pkts_acked(sk, pkts_acked, rtt_us);
 70 }
 71 
 72 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 73 {
 74         struct tcp_sock *tp = tcp_sk(sk);
 75         struct yeah *yeah = inet_csk_ca(sk);
 76 
 77         if (!tcp_is_cwnd_limited(sk, in_flight))
 78                 return;
 79 
 80         if (tp->snd_cwnd <= tp->snd_ssthresh)
 81                 tcp_slow_start(tp);
 82 
 83         else if (!yeah->doing_reno_now) {
 84                 /* Scalable */
 85 
 86                 tp->snd_cwnd_cnt += yeah->pkts_acked;
 87                 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
 88                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 89                                 tp->snd_cwnd++;
 90                         tp->snd_cwnd_cnt = 0;
 91                 }
 92 
 93                 yeah->pkts_acked = 1;
 94 
 95         } else {
 96                 /* Reno */
 97                 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
 98         }
 99 
100         /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
101          *
102          * These are so named because they represent the approximate values
103          * of snd_una and snd_nxt at the beginning of the current RTT. More
104          * precisely, they represent the amount of data sent during the RTT.
105          * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
106          * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
107          * bytes of data have been ACKed during the course of the RTT, giving
108          * an "actual" rate of:
109          *
110          *     (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
111          *
112          * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
113          * because delayed ACKs can cover more than one segment, so they
114          * don't line up yeahly with the boundaries of RTTs.
115          *
116          * Another unfortunate fact of life is that delayed ACKs delay the
117          * advance of the left edge of our send window, so that the number
118          * of bytes we send in an RTT is often less than our cwnd will allow.
119          * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
120          */
121 
122         if (after(ack, yeah->vegas.beg_snd_nxt)) {
123 
124                 /* We do the Vegas calculations only if we got enough RTT
125                  * samples that we can be reasonably sure that we got
126                  * at least one RTT sample that wasn't from a delayed ACK.
127                  * If we only had 2 samples total,
128                  * then that means we're getting only 1 ACK per RTT, which
129                  * means they're almost certainly delayed ACKs.
130                  * If  we have 3 samples, we should be OK.
131                  */
132 
133                 if (yeah->vegas.cntRTT > 2) {
134                         u32 rtt, queue;
135                         u64 bw;
136 
137                         /* We have enough RTT samples, so, using the Vegas
138                          * algorithm, we determine if we should increase or
139                          * decrease cwnd, and by how much.
140                          */
141 
142                         /* Pluck out the RTT we are using for the Vegas
143                          * calculations. This is the min RTT seen during the
144                          * last RTT. Taking the min filters out the effects
145                          * of delayed ACKs, at the cost of noticing congestion
146                          * a bit later.
147                          */
148                         rtt = yeah->vegas.minRTT;
149 
150                         /* Compute excess number of packets above bandwidth
151                          * Avoid doing full 64 bit divide.
152                          */
153                         bw = tp->snd_cwnd;
154                         bw *= rtt - yeah->vegas.baseRTT;
155                         do_div(bw, rtt);
156                         queue = bw;
157 
158                         if (queue > TCP_YEAH_ALPHA ||
159                             rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
160                                 if (queue > TCP_YEAH_ALPHA &&
161                                     tp->snd_cwnd > yeah->reno_count) {
162                                         u32 reduction = min(queue / TCP_YEAH_GAMMA ,
163                                                             tp->snd_cwnd >> TCP_YEAH_EPSILON);
164 
165                                         tp->snd_cwnd -= reduction;
166 
167                                         tp->snd_cwnd = max(tp->snd_cwnd,
168                                                            yeah->reno_count);
169 
170                                         tp->snd_ssthresh = tp->snd_cwnd;
171                                 }
172 
173                                 if (yeah->reno_count <= 2)
174                                         yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
175                                 else
176                                         yeah->reno_count++;
177 
178                                 yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
179                                                            0xffffffU);
180                         } else {
181                                 yeah->fast_count++;
182 
183                                 if (yeah->fast_count > TCP_YEAH_ZETA) {
184                                         yeah->reno_count = 2;
185                                         yeah->fast_count = 0;
186                                 }
187 
188                                 yeah->doing_reno_now = 0;
189                         }
190 
191                         yeah->lastQ = queue;
192 
193                 }
194 
195                 /* Save the extent of the current window so we can use this
196                  * at the end of the next RTT.
197                  */
198                 yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
199                 yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
200                 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
201 
202                 /* Wipe the slate clean for the next RTT. */
203                 yeah->vegas.cntRTT = 0;
204                 yeah->vegas.minRTT = 0x7fffffff;
205         }
206 }
207 
208 static u32 tcp_yeah_ssthresh(struct sock *sk) {
209         const struct tcp_sock *tp = tcp_sk(sk);
210         struct yeah *yeah = inet_csk_ca(sk);
211         u32 reduction;
212 
213         if (yeah->doing_reno_now < TCP_YEAH_RHO) {
214                 reduction = yeah->lastQ;
215 
216                 reduction = min( reduction, max(tp->snd_cwnd>>1, 2U) );
217 
218                 reduction = max( reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
219         } else
220                 reduction = max(tp->snd_cwnd>>1, 2U);
221 
222         yeah->fast_count = 0;
223         yeah->reno_count = max(yeah->reno_count>>1, 2U);
224 
225         return max_t(int, tp->snd_cwnd - reduction, 2);
226 }
227 
228 static struct tcp_congestion_ops tcp_yeah __read_mostly = {
229         .flags          = TCP_CONG_RTT_STAMP,
230         .init           = tcp_yeah_init,
231         .ssthresh       = tcp_yeah_ssthresh,
232         .cong_avoid     = tcp_yeah_cong_avoid,
233         .min_cwnd       = tcp_reno_min_cwnd,
234         .set_state      = tcp_vegas_state,
235         .cwnd_event     = tcp_vegas_cwnd_event,
236         .get_info       = tcp_vegas_get_info,
237         .pkts_acked     = tcp_yeah_pkts_acked,
238 
239         .owner          = THIS_MODULE,
240         .name           = "yeah",
241 };
242 
243 static int __init tcp_yeah_register(void)
244 {
245         BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
246         tcp_register_congestion_control(&tcp_yeah);
247         return 0;
248 }
249 
250 static void __exit tcp_yeah_unregister(void)
251 {
252         tcp_unregister_congestion_control(&tcp_yeah);
253 }
254 
255 module_init(tcp_yeah_register);
256 module_exit(tcp_yeah_unregister);
257 
258 MODULE_AUTHOR("Angelo P. Castellani");
259 MODULE_LICENSE("GPL");
260 MODULE_DESCRIPTION("YeAH TCP");
261 

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