1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 *
4 * YeAH TCP
5 *
6 * For further details look at:
7 * https://web.archive.org/web/20080316215752/http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
8 *
9 */
10 #include <linux/mm.h>
11 #include <linux/module.h>
12 #include <linux/skbuff.h>
13 #include <linux/inet_diag.h>
14
15 #include <net/tcp.h>
16
17 #include "tcp_vegas.h"
18
19 #define TCP_YEAH_ALPHA 80 /* number of packets queued at the bottleneck */
20 #define TCP_YEAH_GAMMA 1 /* fraction of queue to be removed per rtt */
21 #define TCP_YEAH_DELTA 3 /* log minimum fraction of cwnd to be removed on loss */
22 #define TCP_YEAH_EPSILON 1 /* log maximum fraction to be removed on early decongestion */
23 #define TCP_YEAH_PHY 8 /* maximum delta from base */
24 #define TCP_YEAH_RHO 16 /* minimum number of consecutive rtt to consider competition on loss */
25 #define TCP_YEAH_ZETA 50 /* minimum number of state switches to reset reno_count */
26
27 #define TCP_SCALABLE_AI_CNT 100U
28
29 /* YeAH variables */
30 struct yeah {
31 struct vegas vegas; /* must be first */
32
33 /* YeAH */
34 u32 lastQ;
35 u32 doing_reno_now;
36
37 u32 reno_count;
38 u32 fast_count;
39
40 u32 pkts_acked;
41 };
42
43 static void tcp_yeah_init(struct sock *sk)
44 {
45 struct tcp_sock *tp = tcp_sk(sk);
46 struct yeah *yeah = inet_csk_ca(sk);
47
48 tcp_vegas_init(sk);
49
50 yeah->doing_reno_now = 0;
51 yeah->lastQ = 0;
52
53 yeah->reno_count = 2;
54
55 /* Ensure the MD arithmetic works. This is somewhat pedantic,
56 * since I don't think we will see a cwnd this large. :) */
57 tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
58 }
59
60 static void tcp_yeah_pkts_acked(struct sock *sk,
61 const struct ack_sample *sample)
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 = sample->pkts_acked;
68
69 tcp_vegas_pkts_acked(sk, sample);
70 }
71
72 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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))
78 return;
79
80 if (tcp_in_slow_start(tp))
81 tcp_slow_start(tp, acked);
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, 1);
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 /* We do the Vegas calculations only if we got enough RTT
124 * samples that we can be reasonably sure that we got
125 * at least one RTT sample that wasn't from a delayed ACK.
126 * If we only had 2 samples total,
127 * then that means we're getting only 1 ACK per RTT, which
128 * means they're almost certainly delayed ACKs.
129 * If we have 3 samples, we should be OK.
130 */
131
132 if (yeah->vegas.cntRTT > 2) {
133 u32 rtt, queue;
134 u64 bw;
135
136 /* We have enough RTT samples, so, using the Vegas
137 * algorithm, we determine if we should increase or
138 * decrease cwnd, and by how much.
139 */
140
141 /* Pluck out the RTT we are using for the Vegas
142 * calculations. This is the min RTT seen during the
143 * last RTT. Taking the min filters out the effects
144 * of delayed ACKs, at the cost of noticing congestion
145 * a bit later.
146 */
147 rtt = yeah->vegas.minRTT;
148
149 /* Compute excess number of packets above bandwidth
150 * Avoid doing full 64 bit divide.
151 */
152 bw = tp->snd_cwnd;
153 bw *= rtt - yeah->vegas.baseRTT;
154 do_div(bw, rtt);
155 queue = bw;
156
157 if (queue > TCP_YEAH_ALPHA ||
158 rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
159 if (queue > TCP_YEAH_ALPHA &&
160 tp->snd_cwnd > yeah->reno_count) {
161 u32 reduction = min(queue / TCP_YEAH_GAMMA ,
162 tp->snd_cwnd >> TCP_YEAH_EPSILON);
163
164 tp->snd_cwnd -= reduction;
165
166 tp->snd_cwnd = max(tp->snd_cwnd,
167 yeah->reno_count);
168
169 tp->snd_ssthresh = tp->snd_cwnd;
170 }
171
172 if (yeah->reno_count <= 2)
173 yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
174 else
175 yeah->reno_count++;
176
177 yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
178 0xffffffU);
179 } else {
180 yeah->fast_count++;
181
182 if (yeah->fast_count > TCP_YEAH_ZETA) {
183 yeah->reno_count = 2;
184 yeah->fast_count = 0;
185 }
186
187 yeah->doing_reno_now = 0;
188 }
189
190 yeah->lastQ = queue;
191 }
192
193 /* Save the extent of the current window so we can use this
194 * at the end of the next RTT.
195 */
196 yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt;
197 yeah->vegas.beg_snd_nxt = tp->snd_nxt;
198 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
199
200 /* Wipe the slate clean for the next RTT. */
201 yeah->vegas.cntRTT = 0;
202 yeah->vegas.minRTT = 0x7fffffff;
203 }
204 }
205
206 static u32 tcp_yeah_ssthresh(struct sock *sk)
207 {
208 const struct tcp_sock *tp = tcp_sk(sk);
209 struct yeah *yeah = inet_csk_ca(sk);
210 u32 reduction;
211
212 if (yeah->doing_reno_now < TCP_YEAH_RHO) {
213 reduction = yeah->lastQ;
214
215 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
216
217 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
218 } else
219 reduction = max(tp->snd_cwnd>>1, 2U);
220
221 yeah->fast_count = 0;
222 yeah->reno_count = max(yeah->reno_count>>1, 2U);
223
224 return max_t(int, tp->snd_cwnd - reduction, 2);
225 }
226
227 static struct tcp_congestion_ops tcp_yeah __read_mostly = {
228 .init = tcp_yeah_init,
229 .ssthresh = tcp_yeah_ssthresh,
230 .undo_cwnd = tcp_reno_undo_cwnd,
231 .cong_avoid = tcp_yeah_cong_avoid,
232 .set_state = tcp_vegas_state,
233 .cwnd_event = tcp_vegas_cwnd_event,
234 .get_info = tcp_vegas_get_info,
235 .pkts_acked = tcp_yeah_pkts_acked,
236
237 .owner = THIS_MODULE,
238 .name = "yeah",
239 };
240
241 static int __init tcp_yeah_register(void)
242 {
243 BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
244 tcp_register_congestion_control(&tcp_yeah);
245 return 0;
246 }
247
248 static void __exit tcp_yeah_unregister(void)
249 {
250 tcp_unregister_congestion_control(&tcp_yeah);
251 }
252
253 module_init(tcp_yeah_register);
254 module_exit(tcp_yeah_unregister);
255
256 MODULE_AUTHOR("Angelo P. Castellani");
257 MODULE_LICENSE("GPL");
258 MODULE_DESCRIPTION("YeAH TCP");