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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 */
30struct 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
41static 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
58static 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(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
75 acked);
76 } else {
77 /* Reno */
78 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 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 */
102do_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 = tp->snd_cwnd;
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 tp->snd_cwnd > yeah->reno_count) {
142 u32 reduction = min(queue / TCP_YEAH_GAMMA ,
143 tp->snd_cwnd >> TCP_YEAH_EPSILON);
144
145 tp->snd_cwnd -= reduction;
146
147 tp->snd_cwnd = max(tp->snd_cwnd,
148 yeah->reno_count);
149
150 tp->snd_ssthresh = tp->snd_cwnd;
151 }
152
153 if (yeah->reno_count <= 2)
154 yeah->reno_count = max(tp->snd_cwnd>>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 = tp->snd_cwnd;
180
181 /* Wipe the slate clean for the next RTT. */
182 yeah->vegas.cntRTT = 0;
183 yeah->vegas.minRTT = 0x7fffffff;
184 }
185}
186
187static 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(tp->snd_cwnd>>1, 2U));
197
198 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
199 } else
200 reduction = max(tp->snd_cwnd>>1, 2U);
201
202 yeah->fast_count = 0;
203 yeah->reno_count = max(yeah->reno_count>>1, 2U);
204
205 return max_t(int, tp->snd_cwnd - reduction, 2);
206}
207
208static 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
222static int __init tcp_yeah_register(void)
223{
224 BUILD_BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
225 tcp_register_congestion_control(&tcp_yeah);
226 return 0;
227}
228
229static void __exit tcp_yeah_unregister(void)
230{
231 tcp_unregister_congestion_control(&tcp_yeah);
232}
233
234module_init(tcp_yeah_register);
235module_exit(tcp_yeah_unregister);
236
237MODULE_AUTHOR("Angelo P. Castellani");
238MODULE_LICENSE("GPL");
239MODULE_DESCRIPTION("YeAH TCP");
1/*
2 *
3 * YeAH TCP
4 *
5 * For further details look at:
6 * https://web.archive.org/web/20080316215752/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 /* number of packets queued at the bottleneck */
19#define TCP_YEAH_GAMMA 1 /* 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 /* maximum delta from base */
23#define TCP_YEAH_RHO 16 /* minimum number of consecutive rtt to consider competition on loss */
24#define TCP_YEAH_ZETA 50 /* minimum number of state switches to reset reno_count */
25
26#define TCP_SCALABLE_AI_CNT 100U
27
28/* YeAH variables */
29struct 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
42static 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
59static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked, s32 rtt_us)
60{
61 const struct inet_connection_sock *icsk = inet_csk(sk);
62 struct yeah *yeah = inet_csk_ca(sk);
63
64 if (icsk->icsk_ca_state == TCP_CA_Open)
65 yeah->pkts_acked = pkts_acked;
66
67 tcp_vegas_pkts_acked(sk, pkts_acked, rtt_us);
68}
69
70static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked)
71{
72 struct tcp_sock *tp = tcp_sk(sk);
73 struct yeah *yeah = inet_csk_ca(sk);
74
75 if (!tcp_is_cwnd_limited(sk))
76 return;
77
78 if (tp->snd_cwnd <= tp->snd_ssthresh)
79 tcp_slow_start(tp, acked);
80
81 else if (!yeah->doing_reno_now) {
82 /* Scalable */
83
84 tp->snd_cwnd_cnt += yeah->pkts_acked;
85 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)) {
86 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
87 tp->snd_cwnd++;
88 tp->snd_cwnd_cnt = 0;
89 }
90
91 yeah->pkts_acked = 1;
92
93 } else {
94 /* Reno */
95 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1);
96 }
97
98 /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
99 *
100 * These are so named because they represent the approximate values
101 * of snd_una and snd_nxt at the beginning of the current RTT. More
102 * precisely, they represent the amount of data sent during the RTT.
103 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
104 * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
105 * bytes of data have been ACKed during the course of the RTT, giving
106 * an "actual" rate of:
107 *
108 * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
109 *
110 * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
111 * because delayed ACKs can cover more than one segment, so they
112 * don't line up yeahly with the boundaries of RTTs.
113 *
114 * Another unfortunate fact of life is that delayed ACKs delay the
115 * advance of the left edge of our send window, so that the number
116 * of bytes we send in an RTT is often less than our cwnd will allow.
117 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
118 */
119
120 if (after(ack, yeah->vegas.beg_snd_nxt)) {
121 /* We do the Vegas calculations only if we got enough RTT
122 * samples that we can be reasonably sure that we got
123 * at least one RTT sample that wasn't from a delayed ACK.
124 * If we only had 2 samples total,
125 * then that means we're getting only 1 ACK per RTT, which
126 * means they're almost certainly delayed ACKs.
127 * If we have 3 samples, we should be OK.
128 */
129
130 if (yeah->vegas.cntRTT > 2) {
131 u32 rtt, queue;
132 u64 bw;
133
134 /* We have enough RTT samples, so, using the Vegas
135 * algorithm, we determine if we should increase or
136 * decrease cwnd, and by how much.
137 */
138
139 /* Pluck out the RTT we are using for the Vegas
140 * calculations. This is the min RTT seen during the
141 * last RTT. Taking the min filters out the effects
142 * of delayed ACKs, at the cost of noticing congestion
143 * a bit later.
144 */
145 rtt = yeah->vegas.minRTT;
146
147 /* Compute excess number of packets above bandwidth
148 * Avoid doing full 64 bit divide.
149 */
150 bw = tp->snd_cwnd;
151 bw *= rtt - yeah->vegas.baseRTT;
152 do_div(bw, rtt);
153 queue = bw;
154
155 if (queue > TCP_YEAH_ALPHA ||
156 rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
157 if (queue > TCP_YEAH_ALPHA &&
158 tp->snd_cwnd > yeah->reno_count) {
159 u32 reduction = min(queue / TCP_YEAH_GAMMA ,
160 tp->snd_cwnd >> TCP_YEAH_EPSILON);
161
162 tp->snd_cwnd -= reduction;
163
164 tp->snd_cwnd = max(tp->snd_cwnd,
165 yeah->reno_count);
166
167 tp->snd_ssthresh = tp->snd_cwnd;
168 }
169
170 if (yeah->reno_count <= 2)
171 yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
172 else
173 yeah->reno_count++;
174
175 yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
176 0xffffffU);
177 } else {
178 yeah->fast_count++;
179
180 if (yeah->fast_count > TCP_YEAH_ZETA) {
181 yeah->reno_count = 2;
182 yeah->fast_count = 0;
183 }
184
185 yeah->doing_reno_now = 0;
186 }
187
188 yeah->lastQ = queue;
189 }
190
191 /* Save the extent of the current window so we can use this
192 * at the end of the next RTT.
193 */
194 yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt;
195 yeah->vegas.beg_snd_nxt = tp->snd_nxt;
196 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
197
198 /* Wipe the slate clean for the next RTT. */
199 yeah->vegas.cntRTT = 0;
200 yeah->vegas.minRTT = 0x7fffffff;
201 }
202}
203
204static u32 tcp_yeah_ssthresh(struct sock *sk)
205{
206 const struct tcp_sock *tp = tcp_sk(sk);
207 struct yeah *yeah = inet_csk_ca(sk);
208 u32 reduction;
209
210 if (yeah->doing_reno_now < TCP_YEAH_RHO) {
211 reduction = yeah->lastQ;
212
213 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
214
215 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
216 } else
217 reduction = max(tp->snd_cwnd>>1, 2U);
218
219 yeah->fast_count = 0;
220 yeah->reno_count = max(yeah->reno_count>>1, 2U);
221
222 return max_t(int, tp->snd_cwnd - reduction, 2);
223}
224
225static struct tcp_congestion_ops tcp_yeah __read_mostly = {
226 .init = tcp_yeah_init,
227 .ssthresh = tcp_yeah_ssthresh,
228 .cong_avoid = tcp_yeah_cong_avoid,
229 .set_state = tcp_vegas_state,
230 .cwnd_event = tcp_vegas_cwnd_event,
231 .get_info = tcp_vegas_get_info,
232 .pkts_acked = tcp_yeah_pkts_acked,
233
234 .owner = THIS_MODULE,
235 .name = "yeah",
236};
237
238static int __init tcp_yeah_register(void)
239{
240 BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
241 tcp_register_congestion_control(&tcp_yeah);
242 return 0;
243}
244
245static void __exit tcp_yeah_unregister(void)
246{
247 tcp_unregister_congestion_control(&tcp_yeah);
248}
249
250module_init(tcp_yeah_register);
251module_exit(tcp_yeah_unregister);
252
253MODULE_AUTHOR("Angelo P. Castellani");
254MODULE_LICENSE("GPL");
255MODULE_DESCRIPTION("YeAH TCP");