xref: /openbmc/linux/net/ipv4/tcp_yeah.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 minumum 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, ktime_t last)
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, last);
70 }
71 
72 static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack,
73 				u32 seq_rtt, u32 in_flight, int flag)
74 {
75 	struct tcp_sock *tp = tcp_sk(sk);
76 	struct yeah *yeah = inet_csk_ca(sk);
77 
78 	if (!tcp_is_cwnd_limited(sk, in_flight))
79 		return;
80 
81 	if (tp->snd_cwnd <= tp->snd_ssthresh)
82 		tcp_slow_start(tp);
83 
84 	else if (!yeah->doing_reno_now) {
85 		/* Scalable */
86 
87 		tp->snd_cwnd_cnt+=yeah->pkts_acked;
88 		if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
89 			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
90 				tp->snd_cwnd++;
91 			tp->snd_cwnd_cnt = 0;
92 		}
93 
94 		yeah->pkts_acked = 1;
95 
96 	} else {
97 		/* Reno */
98 
99 		if (tp->snd_cwnd_cnt < tp->snd_cwnd)
100 			tp->snd_cwnd_cnt++;
101 
102 		if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
103 			tp->snd_cwnd++;
104 			tp->snd_cwnd_cnt = 0;
105 		}
106 	}
107 
108 	/* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
109 	 *
110 	 * These are so named because they represent the approximate values
111 	 * of snd_una and snd_nxt at the beginning of the current RTT. More
112 	 * precisely, they represent the amount of data sent during the RTT.
113 	 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
114 	 * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
115 	 * bytes of data have been ACKed during the course of the RTT, giving
116 	 * an "actual" rate of:
117 	 *
118 	 *     (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
119 	 *
120 	 * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
121 	 * because delayed ACKs can cover more than one segment, so they
122 	 * don't line up yeahly with the boundaries of RTTs.
123 	 *
124 	 * Another unfortunate fact of life is that delayed ACKs delay the
125 	 * advance of the left edge of our send window, so that the number
126 	 * of bytes we send in an RTT is often less than our cwnd will allow.
127 	 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
128 	 */
129 
130 	if (after(ack, yeah->vegas.beg_snd_nxt)) {
131 
132 		/* We do the Vegas calculations only if we got enough RTT
133 		 * samples that we can be reasonably sure that we got
134 		 * at least one RTT sample that wasn't from a delayed ACK.
135 		 * If we only had 2 samples total,
136 		 * then that means we're getting only 1 ACK per RTT, which
137 		 * means they're almost certainly delayed ACKs.
138 		 * If  we have 3 samples, we should be OK.
139 		 */
140 
141 		if (yeah->vegas.cntRTT > 2) {
142 			u32 rtt, queue;
143 			u64 bw;
144 
145 			/* We have enough RTT samples, so, using the Vegas
146 			 * algorithm, we determine if we should increase or
147 			 * decrease cwnd, and by how much.
148 			 */
149 
150 			/* Pluck out the RTT we are using for the Vegas
151 			 * calculations. This is the min RTT seen during the
152 			 * last RTT. Taking the min filters out the effects
153 			 * of delayed ACKs, at the cost of noticing congestion
154 			 * a bit later.
155 			 */
156 			rtt = yeah->vegas.minRTT;
157 
158 			/* Compute excess number of packets above bandwidth
159 			 * Avoid doing full 64 bit divide.
160 			 */
161 			bw = tp->snd_cwnd;
162 			bw *= rtt - yeah->vegas.baseRTT;
163 			do_div(bw, rtt);
164 			queue = bw;
165 
166 			if (queue > TCP_YEAH_ALPHA ||
167 			    rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
168 				if (queue > TCP_YEAH_ALPHA
169 				    && tp->snd_cwnd > yeah->reno_count) {
170 					u32 reduction = min(queue / TCP_YEAH_GAMMA ,
171 							    tp->snd_cwnd >> TCP_YEAH_EPSILON);
172 
173 					tp->snd_cwnd -= reduction;
174 
175 					tp->snd_cwnd = max(tp->snd_cwnd,
176 							   yeah->reno_count);
177 
178 					tp->snd_ssthresh = tp->snd_cwnd;
179 				}
180 
181 				if (yeah->reno_count <= 2)
182 					yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
183 				else
184 					yeah->reno_count++;
185 
186 				yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
187 							   0xffffffU);
188 			} else {
189 				yeah->fast_count++;
190 
191 				if (yeah->fast_count > TCP_YEAH_ZETA) {
192 					yeah->reno_count = 2;
193 					yeah->fast_count = 0;
194 				}
195 
196 				yeah->doing_reno_now = 0;
197 			}
198 
199 			yeah->lastQ = queue;
200 
201 		}
202 
203 		/* Save the extent of the current window so we can use this
204 		 * at the end of the next RTT.
205 		 */
206 		yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
207 		yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
208 		yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
209 
210 		/* Wipe the slate clean for the next RTT. */
211 		yeah->vegas.cntRTT = 0;
212 		yeah->vegas.minRTT = 0x7fffffff;
213 	}
214 }
215 
216 static u32 tcp_yeah_ssthresh(struct sock *sk) {
217 	const struct tcp_sock *tp = tcp_sk(sk);
218 	struct yeah *yeah = inet_csk_ca(sk);
219 	u32 reduction;
220 
221 	if (yeah->doing_reno_now < TCP_YEAH_RHO) {
222 		reduction = yeah->lastQ;
223 
224 		reduction = min( reduction, max(tp->snd_cwnd>>1, 2U) );
225 
226 		reduction = max( reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
227 	} else
228 		reduction = max(tp->snd_cwnd>>1,2U);
229 
230 	yeah->fast_count = 0;
231 	yeah->reno_count = max(yeah->reno_count>>1, 2U);
232 
233 	return tp->snd_cwnd - reduction;
234 }
235 
236 static struct tcp_congestion_ops tcp_yeah = {
237 	.flags		= TCP_CONG_RTT_STAMP,
238 	.init		= tcp_yeah_init,
239 	.ssthresh	= tcp_yeah_ssthresh,
240 	.cong_avoid	= tcp_yeah_cong_avoid,
241 	.min_cwnd	= tcp_reno_min_cwnd,
242 	.set_state	= tcp_vegas_state,
243 	.cwnd_event	= tcp_vegas_cwnd_event,
244 	.get_info	= tcp_vegas_get_info,
245 	.pkts_acked	= tcp_yeah_pkts_acked,
246 
247 	.owner		= THIS_MODULE,
248 	.name		= "yeah",
249 };
250 
251 static int __init tcp_yeah_register(void)
252 {
253 	BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
254 	tcp_register_congestion_control(&tcp_yeah);
255 	return 0;
256 }
257 
258 static void __exit tcp_yeah_unregister(void)
259 {
260 	tcp_unregister_congestion_control(&tcp_yeah);
261 }
262 
263 module_init(tcp_yeah_register);
264 module_exit(tcp_yeah_unregister);
265 
266 MODULE_AUTHOR("Angelo P. Castellani");
267 MODULE_LICENSE("GPL");
268 MODULE_DESCRIPTION("YeAH TCP");
269