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,
60 const struct ack_sample *sample)
61{
62 const struct inet_connection_sock *icsk = inet_csk(sk);
63 struct yeah *yeah = inet_csk_ca(sk);
64
65 if (icsk->icsk_ca_state == TCP_CA_Open)
66 yeah->pkts_acked = sample->pkts_acked;
67
68 tcp_vegas_pkts_acked(sk, sample);
69}
70
71static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked)
72{
73 struct tcp_sock *tp = tcp_sk(sk);
74 struct yeah *yeah = inet_csk_ca(sk);
75
76 if (!tcp_is_cwnd_limited(sk))
77 return;
78
79 if (tcp_in_slow_start(tp))
80 tcp_slow_start(tp, acked);
81
82 else if (!yeah->doing_reno_now) {
83 /* Scalable */
84
85 tp->snd_cwnd_cnt += yeah->pkts_acked;
86 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)) {
87 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
88 tp->snd_cwnd++;
89 tp->snd_cwnd_cnt = 0;
90 }
91
92 yeah->pkts_acked = 1;
93
94 } else {
95 /* Reno */
96 tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1);
97 }
98
99 /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
100 *
101 * These are so named because they represent the approximate values
102 * of snd_una and snd_nxt at the beginning of the current RTT. More
103 * precisely, they represent the amount of data sent during the RTT.
104 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
105 * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
106 * bytes of data have been ACKed during the course of the RTT, giving
107 * an "actual" rate of:
108 *
109 * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
110 *
111 * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
112 * because delayed ACKs can cover more than one segment, so they
113 * don't line up yeahly with the boundaries of RTTs.
114 *
115 * Another unfortunate fact of life is that delayed ACKs delay the
116 * advance of the left edge of our send window, so that the number
117 * of bytes we send in an RTT is often less than our cwnd will allow.
118 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
119 */
120
121 if (after(ack, yeah->vegas.beg_snd_nxt)) {
122 /* We do the Vegas calculations only if we got enough RTT
123 * samples that we can be reasonably sure that we got
124 * at least one RTT sample that wasn't from a delayed ACK.
125 * If we only had 2 samples total,
126 * then that means we're getting only 1 ACK per RTT, which
127 * means they're almost certainly delayed ACKs.
128 * If we have 3 samples, we should be OK.
129 */
130
131 if (yeah->vegas.cntRTT > 2) {
132 u32 rtt, queue;
133 u64 bw;
134
135 /* We have enough RTT samples, so, using the Vegas
136 * algorithm, we determine if we should increase or
137 * decrease cwnd, and by how much.
138 */
139
140 /* Pluck out the RTT we are using for the Vegas
141 * calculations. This is the min RTT seen during the
142 * last RTT. Taking the min filters out the effects
143 * of delayed ACKs, at the cost of noticing congestion
144 * a bit later.
145 */
146 rtt = yeah->vegas.minRTT;
147
148 /* Compute excess number of packets above bandwidth
149 * Avoid doing full 64 bit divide.
150 */
151 bw = tp->snd_cwnd;
152 bw *= rtt - yeah->vegas.baseRTT;
153 do_div(bw, rtt);
154 queue = bw;
155
156 if (queue > TCP_YEAH_ALPHA ||
157 rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
158 if (queue > TCP_YEAH_ALPHA &&
159 tp->snd_cwnd > yeah->reno_count) {
160 u32 reduction = min(queue / TCP_YEAH_GAMMA ,
161 tp->snd_cwnd >> TCP_YEAH_EPSILON);
162
163 tp->snd_cwnd -= reduction;
164
165 tp->snd_cwnd = max(tp->snd_cwnd,
166 yeah->reno_count);
167
168 tp->snd_ssthresh = tp->snd_cwnd;
169 }
170
171 if (yeah->reno_count <= 2)
172 yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
173 else
174 yeah->reno_count++;
175
176 yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
177 0xffffffU);
178 } else {
179 yeah->fast_count++;
180
181 if (yeah->fast_count > TCP_YEAH_ZETA) {
182 yeah->reno_count = 2;
183 yeah->fast_count = 0;
184 }
185
186 yeah->doing_reno_now = 0;
187 }
188
189 yeah->lastQ = queue;
190 }
191
192 /* Save the extent of the current window so we can use this
193 * at the end of the next RTT.
194 */
195 yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt;
196 yeah->vegas.beg_snd_nxt = tp->snd_nxt;
197 yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
198
199 /* Wipe the slate clean for the next RTT. */
200 yeah->vegas.cntRTT = 0;
201 yeah->vegas.minRTT = 0x7fffffff;
202 }
203}
204
205static u32 tcp_yeah_ssthresh(struct sock *sk)
206{
207 const struct tcp_sock *tp = tcp_sk(sk);
208 struct yeah *yeah = inet_csk_ca(sk);
209 u32 reduction;
210
211 if (yeah->doing_reno_now < TCP_YEAH_RHO) {
212 reduction = yeah->lastQ;
213
214 reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
215
216 reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
217 } else
218 reduction = max(tp->snd_cwnd>>1, 2U);
219
220 yeah->fast_count = 0;
221 yeah->reno_count = max(yeah->reno_count>>1, 2U);
222
223 return max_t(int, tp->snd_cwnd - reduction, 2);
224}
225
226static struct tcp_congestion_ops tcp_yeah __read_mostly = {
227 .init = tcp_yeah_init,
228 .ssthresh = tcp_yeah_ssthresh,
229 .undo_cwnd = tcp_reno_undo_cwnd,
230 .cong_avoid = tcp_yeah_cong_avoid,
231 .set_state = tcp_vegas_state,
232 .cwnd_event = tcp_vegas_cwnd_event,
233 .get_info = tcp_vegas_get_info,
234 .pkts_acked = tcp_yeah_pkts_acked,
235
236 .owner = THIS_MODULE,
237 .name = "yeah",
238};
239
240static int __init tcp_yeah_register(void)
241{
242 BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
243 tcp_register_congestion_control(&tcp_yeah);
244 return 0;
245}
246
247static void __exit tcp_yeah_unregister(void)
248{
249 tcp_unregister_congestion_control(&tcp_yeah);
250}
251
252module_init(tcp_yeah_register);
253module_exit(tcp_yeah_unregister);
254
255MODULE_AUTHOR("Angelo P. Castellani");
256MODULE_LICENSE("GPL");
257MODULE_DESCRIPTION("YeAH TCP");
258