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 | |
41 | static void tcp_yeah_init(struct sock *sk) |
42 | { |
43 | struct tcp_sock *tp = tcp_sk(sk); |
44 | struct yeah *yeah = inet_csk_ca(sk); |
45 | |
46 | tcp_vegas_init(sk); |
47 | |
48 | yeah->doing_reno_now = 0; |
49 | yeah->lastQ = 0; |
50 | |
51 | yeah->reno_count = 2; |
52 | |
53 | /* Ensure the MD arithmetic works. This is somewhat pedantic, |
54 | * since I don't think we will see a cwnd this large. :) */ |
55 | tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128); |
56 | } |
57 | |
58 | static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked) |
59 | { |
60 | struct tcp_sock *tp = tcp_sk(sk); |
61 | struct yeah *yeah = inet_csk_ca(sk); |
62 | |
63 | if (!tcp_is_cwnd_limited(sk)) |
64 | return; |
65 | |
66 | if (tcp_in_slow_start(tp)) { |
67 | acked = tcp_slow_start(tp, acked); |
68 | if (!acked) |
69 | goto do_vegas; |
70 | } |
71 | |
72 | if (!yeah->doing_reno_now) { |
73 | /* Scalable */ |
74 | tcp_cong_avoid_ai(tp, min(tcp_snd_cwnd(tp), TCP_SCALABLE_AI_CNT), |
75 | acked); |
76 | } else { |
77 | /* Reno */ |
78 | tcp_cong_avoid_ai(tp, w: tcp_snd_cwnd(tp), acked); |
79 | } |
80 | |
81 | /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt. |
82 | * |
83 | * These are so named because they represent the approximate values |
84 | * of snd_una and snd_nxt at the beginning of the current RTT. More |
85 | * precisely, they represent the amount of data sent during the RTT. |
86 | * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, |
87 | * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding |
88 | * bytes of data have been ACKed during the course of the RTT, giving |
89 | * an "actual" rate of: |
90 | * |
91 | * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration) |
92 | * |
93 | * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una, |
94 | * because delayed ACKs can cover more than one segment, so they |
95 | * don't line up yeahly with the boundaries of RTTs. |
96 | * |
97 | * Another unfortunate fact of life is that delayed ACKs delay the |
98 | * advance of the left edge of our send window, so that the number |
99 | * of bytes we send in an RTT is often less than our cwnd will allow. |
100 | * So we keep track of our cwnd separately, in v_beg_snd_cwnd. |
101 | */ |
102 | do_vegas: |
103 | if (after(ack, yeah->vegas.beg_snd_nxt)) { |
104 | /* We do the Vegas calculations only if we got enough RTT |
105 | * samples that we can be reasonably sure that we got |
106 | * at least one RTT sample that wasn't from a delayed ACK. |
107 | * If we only had 2 samples total, |
108 | * then that means we're getting only 1 ACK per RTT, which |
109 | * means they're almost certainly delayed ACKs. |
110 | * If we have 3 samples, we should be OK. |
111 | */ |
112 | |
113 | if (yeah->vegas.cntRTT > 2) { |
114 | u32 rtt, queue; |
115 | u64 bw; |
116 | |
117 | /* We have enough RTT samples, so, using the Vegas |
118 | * algorithm, we determine if we should increase or |
119 | * decrease cwnd, and by how much. |
120 | */ |
121 | |
122 | /* Pluck out the RTT we are using for the Vegas |
123 | * calculations. This is the min RTT seen during the |
124 | * last RTT. Taking the min filters out the effects |
125 | * of delayed ACKs, at the cost of noticing congestion |
126 | * a bit later. |
127 | */ |
128 | rtt = yeah->vegas.minRTT; |
129 | |
130 | /* Compute excess number of packets above bandwidth |
131 | * Avoid doing full 64 bit divide. |
132 | */ |
133 | bw = tcp_snd_cwnd(tp); |
134 | bw *= rtt - yeah->vegas.baseRTT; |
135 | do_div(bw, rtt); |
136 | queue = bw; |
137 | |
138 | if (queue > TCP_YEAH_ALPHA || |
139 | rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { |
140 | if (queue > TCP_YEAH_ALPHA && |
141 | tcp_snd_cwnd(tp) > yeah->reno_count) { |
142 | u32 reduction = min(queue / TCP_YEAH_GAMMA , |
143 | tcp_snd_cwnd(tp) >> TCP_YEAH_EPSILON); |
144 | |
145 | tcp_snd_cwnd_set(tp, val: tcp_snd_cwnd(tp) - reduction); |
146 | |
147 | tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp), |
148 | yeah->reno_count)); |
149 | |
150 | tp->snd_ssthresh = tcp_snd_cwnd(tp); |
151 | } |
152 | |
153 | if (yeah->reno_count <= 2) |
154 | yeah->reno_count = max(tcp_snd_cwnd(tp)>>1, 2U); |
155 | else |
156 | yeah->reno_count++; |
157 | |
158 | yeah->doing_reno_now = min(yeah->doing_reno_now + 1, |
159 | 0xffffffU); |
160 | } else { |
161 | yeah->fast_count++; |
162 | |
163 | if (yeah->fast_count > TCP_YEAH_ZETA) { |
164 | yeah->reno_count = 2; |
165 | yeah->fast_count = 0; |
166 | } |
167 | |
168 | yeah->doing_reno_now = 0; |
169 | } |
170 | |
171 | yeah->lastQ = queue; |
172 | } |
173 | |
174 | /* Save the extent of the current window so we can use this |
175 | * at the end of the next RTT. |
176 | */ |
177 | yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; |
178 | yeah->vegas.beg_snd_nxt = tp->snd_nxt; |
179 | yeah->vegas.beg_snd_cwnd = tcp_snd_cwnd(tp); |
180 | |
181 | /* Wipe the slate clean for the next RTT. */ |
182 | yeah->vegas.cntRTT = 0; |
183 | yeah->vegas.minRTT = 0x7fffffff; |
184 | } |
185 | } |
186 | |
187 | static u32 tcp_yeah_ssthresh(struct sock *sk) |
188 | { |
189 | const struct tcp_sock *tp = tcp_sk(sk); |
190 | struct yeah *yeah = inet_csk_ca(sk); |
191 | u32 reduction; |
192 | |
193 | if (yeah->doing_reno_now < TCP_YEAH_RHO) { |
194 | reduction = yeah->lastQ; |
195 | |
196 | reduction = min(reduction, max(tcp_snd_cwnd(tp)>>1, 2U)); |
197 | |
198 | reduction = max(reduction, tcp_snd_cwnd(tp) >> TCP_YEAH_DELTA); |
199 | } else |
200 | reduction = max(tcp_snd_cwnd(tp)>>1, 2U); |
201 | |
202 | yeah->fast_count = 0; |
203 | yeah->reno_count = max(yeah->reno_count>>1, 2U); |
204 | |
205 | return max_t(int, tcp_snd_cwnd(tp) - reduction, 2); |
206 | } |
207 | |
208 | static struct tcp_congestion_ops tcp_yeah __read_mostly = { |
209 | .init = tcp_yeah_init, |
210 | .ssthresh = tcp_yeah_ssthresh, |
211 | .undo_cwnd = tcp_reno_undo_cwnd, |
212 | .cong_avoid = tcp_yeah_cong_avoid, |
213 | .set_state = tcp_vegas_state, |
214 | .cwnd_event = tcp_vegas_cwnd_event, |
215 | .get_info = tcp_vegas_get_info, |
216 | .pkts_acked = tcp_vegas_pkts_acked, |
217 | |
218 | .owner = THIS_MODULE, |
219 | .name = "yeah" , |
220 | }; |
221 | |
222 | static int __init tcp_yeah_register(void) |
223 | { |
224 | BUILD_BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); |
225 | tcp_register_congestion_control(type: &tcp_yeah); |
226 | return 0; |
227 | } |
228 | |
229 | static void __exit tcp_yeah_unregister(void) |
230 | { |
231 | tcp_unregister_congestion_control(type: &tcp_yeah); |
232 | } |
233 | |
234 | module_init(tcp_yeah_register); |
235 | module_exit(tcp_yeah_unregister); |
236 | |
237 | MODULE_AUTHOR("Angelo P. Castellani" ); |
238 | MODULE_LICENSE("GPL" ); |
239 | MODULE_DESCRIPTION("YeAH TCP" ); |
240 | |