1/*
2 * TCP Veno congestion control
3 *
4 * This is based on the congestion detection/avoidance scheme described in
5 *    C. P. Fu, S. C. Liew.
6 *    "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
7 *    IEEE Journal on Selected Areas in Communication,
8 *    Feb. 2003.
9 * 	See http://www.ntu.edu.sg/home5/ZHOU0022/papers/CPFu03a.pdf
10 */
11
12#include <linux/mm.h>
13#include <linux/module.h>
14#include <linux/skbuff.h>
15#include <linux/inet_diag.h>
16
17#include <net/tcp.h>
18
19/* Default values of the Veno variables, in fixed-point representation
20 * with V_PARAM_SHIFT bits to the right of the binary point.
21 */
22#define V_PARAM_SHIFT 1
23static const int beta = 3 << V_PARAM_SHIFT;
24
25/* Veno variables */
26struct veno {
27	u8 doing_veno_now;	/* if true, do veno for this rtt */
28	u16 cntrtt;		/* # of rtts measured within last rtt */
29	u32 minrtt;		/* min of rtts measured within last rtt (in usec) */
30	u32 basertt;		/* the min of all Veno rtt measurements seen (in usec) */
31	u32 inc;		/* decide whether to increase cwnd */
32	u32 diff;		/* calculate the diff rate */
33};
34
35/* There are several situations when we must "re-start" Veno:
36 *
37 *  o when a connection is established
38 *  o after an RTO
39 *  o after fast recovery
40 *  o when we send a packet and there is no outstanding
41 *    unacknowledged data (restarting an idle connection)
42 *
43 */
44static inline void veno_enable(struct sock *sk)
45{
46	struct veno *veno = inet_csk_ca(sk);
47
48	/* turn on Veno */
49	veno->doing_veno_now = 1;
50
51	veno->minrtt = 0x7fffffff;
52}
53
54static inline void veno_disable(struct sock *sk)
55{
56	struct veno *veno = inet_csk_ca(sk);
57
58	/* turn off Veno */
59	veno->doing_veno_now = 0;
60}
61
62static void tcp_veno_init(struct sock *sk)
63{
64	struct veno *veno = inet_csk_ca(sk);
65
66	veno->basertt = 0x7fffffff;
67	veno->inc = 1;
68	veno_enable(sk);
69}
70
71/* Do rtt sampling needed for Veno. */
72static void tcp_veno_pkts_acked(struct sock *sk, u32 cnt, ktime_t last)
73{
74	struct veno *veno = inet_csk_ca(sk);
75	u32 vrtt;
76
77	if (ktime_equal(last, net_invalid_timestamp()))
78		return;
79
80	/* Never allow zero rtt or baseRTT */
81	vrtt = ktime_to_us(net_timedelta(last)) + 1;
82
83	/* Filter to find propagation delay: */
84	if (vrtt < veno->basertt)
85		veno->basertt = vrtt;
86
87	/* Find the min rtt during the last rtt to find
88	 * the current prop. delay + queuing delay:
89	 */
90	veno->minrtt = min(veno->minrtt, vrtt);
91	veno->cntrtt++;
92}
93
94static void tcp_veno_state(struct sock *sk, u8 ca_state)
95{
96	if (ca_state == TCP_CA_Open)
97		veno_enable(sk);
98	else
99		veno_disable(sk);
100}
101
102/*
103 * If the connection is idle and we are restarting,
104 * then we don't want to do any Veno calculations
105 * until we get fresh rtt samples.  So when we
106 * restart, we reset our Veno state to a clean
107 * state. After we get acks for this flight of
108 * packets, _then_ we can make Veno calculations
109 * again.
110 */
111static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
112{
113	if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
114		tcp_veno_init(sk);
115}
116
117static void tcp_veno_cong_avoid(struct sock *sk, u32 ack,
118				u32 seq_rtt, u32 in_flight, int flag)
119{
120	struct tcp_sock *tp = tcp_sk(sk);
121	struct veno *veno = inet_csk_ca(sk);
122
123	if (!veno->doing_veno_now)
124		return tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
125
126	/* limited by applications */
127	if (!tcp_is_cwnd_limited(sk, in_flight))
128		return;
129
130	/* We do the Veno calculations only if we got enough rtt samples */
131	if (veno->cntrtt <= 2) {
132		/* We don't have enough rtt samples to do the Veno
133		 * calculation, so we'll behave like Reno.
134		 */
135		tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
136	} else {
137		u32 rtt, target_cwnd;
138
139		/* We have enough rtt samples, so, using the Veno
140		 * algorithm, we determine the state of the network.
141		 */
142
143		rtt = veno->minrtt;
144
145		target_cwnd = ((tp->snd_cwnd * veno->basertt)
146			       << V_PARAM_SHIFT) / rtt;
147
148		veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
149
150		if (tp->snd_cwnd <= tp->snd_ssthresh) {
151			/* Slow start.  */
152			tcp_slow_start(tp);
153		} else {
154			/* Congestion avoidance. */
155			if (veno->diff < beta) {
156				/* In the "non-congestive state", increase cwnd
157				 *  every rtt.
158				 */
159				if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
160					if (tp->snd_cwnd < tp->snd_cwnd_clamp)
161						tp->snd_cwnd++;
162					tp->snd_cwnd_cnt = 0;
163				} else
164					tp->snd_cwnd_cnt++;
165			} else {
166				/* In the "congestive state", increase cwnd
167				 * every other rtt.
168				 */
169				if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
170					if (veno->inc
171					    && tp->snd_cwnd <
172					    tp->snd_cwnd_clamp) {
173						tp->snd_cwnd++;
174						veno->inc = 0;
175					} else
176						veno->inc = 1;
177					tp->snd_cwnd_cnt = 0;
178				} else
179					tp->snd_cwnd_cnt++;
180			}
181
182		}
183		if (tp->snd_cwnd < 2)
184			tp->snd_cwnd = 2;
185		else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
186			tp->snd_cwnd = tp->snd_cwnd_clamp;
187	}
188	/* Wipe the slate clean for the next rtt. */
189	/* veno->cntrtt = 0; */
190	veno->minrtt = 0x7fffffff;
191}
192
193/* Veno MD phase */
194static u32 tcp_veno_ssthresh(struct sock *sk)
195{
196	const struct tcp_sock *tp = tcp_sk(sk);
197	struct veno *veno = inet_csk_ca(sk);
198
199	if (veno->diff < beta)
200		/* in "non-congestive state", cut cwnd by 1/5 */
201		return max(tp->snd_cwnd * 4 / 5, 2U);
202	else
203		/* in "congestive state", cut cwnd by 1/2 */
204		return max(tp->snd_cwnd >> 1U, 2U);
205}
206
207static struct tcp_congestion_ops tcp_veno = {
208	.flags		= TCP_CONG_RTT_STAMP,
209	.init		= tcp_veno_init,
210	.ssthresh	= tcp_veno_ssthresh,
211	.cong_avoid	= tcp_veno_cong_avoid,
212	.pkts_acked	= tcp_veno_pkts_acked,
213	.set_state	= tcp_veno_state,
214	.cwnd_event	= tcp_veno_cwnd_event,
215
216	.owner		= THIS_MODULE,
217	.name		= "veno",
218};
219
220static int __init tcp_veno_register(void)
221{
222	BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
223	tcp_register_congestion_control(&tcp_veno);
224	return 0;
225}
226
227static void __exit tcp_veno_unregister(void)
228{
229	tcp_unregister_congestion_control(&tcp_veno);
230}
231
232module_init(tcp_veno_register);
233module_exit(tcp_veno_unregister);
234
235MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
236MODULE_LICENSE("GPL");
237MODULE_DESCRIPTION("TCP Veno");
238