1/*
2 * TCP Low Priority (TCP-LP)
3 *
4 * TCP Low Priority is a distributed algorithm whose goal is to utilize only
5 *   the excess network bandwidth as compared to the ``fair share`` of
6 *   bandwidth as targeted by TCP.
7 *
8 * As of 2.6.13, Linux supports pluggable congestion control algorithms.
9 * Due to the limitation of the API, we take the following changes from
10 * the original TCP-LP implementation:
11 *   o We use newReno in most core CA handling. Only add some checking
12 *     within cong_avoid.
13 *   o Error correcting in remote HZ, therefore remote HZ will be keeped
14 *     on checking and updating.
15 *   o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since
16 *     OWD have a similar meaning as RTT. Also correct the buggy formular.
17 *   o Handle reaction for Early Congestion Indication (ECI) within
18 *     pkts_acked, as mentioned within pseudo code.
19 *   o OWD is handled in relative format, where local time stamp will in
20 *     tcp_time_stamp format.
21 *
22 * Original Author:
23 *   Aleksandar Kuzmanovic <akuzma@northwestern.edu>
24 * Available from:
25 *   http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf
26 * Original implementation for 2.4.19:
27 *   http://www-ece.rice.edu/networks/TCP-LP/
28 *
29 * 2.6.x module Authors:
30 *   Wong Hoi Sing, Edison <hswong3i@gmail.com>
31 *   Hung Hing Lun, Mike <hlhung3i@gmail.com>
32 * SourceForge project page:
33 *   http://tcp-lp-mod.sourceforge.net/
34 */
35
36#include <linux/module.h>
37#include <net/tcp.h>
38
39/* resolution of owd */
40#define LP_RESOL       1000
41
42/**
43 * enum tcp_lp_state
44 * @LP_VALID_RHZ: is remote HZ valid?
45 * @LP_VALID_OWD: is OWD valid?
46 * @LP_WITHIN_THR: are we within threshold?
47 * @LP_WITHIN_INF: are we within inference?
48 *
49 * TCP-LP's state flags.
50 * We create this set of state flag mainly for debugging.
51 */
52enum tcp_lp_state {
53	LP_VALID_RHZ = (1 << 0),
54	LP_VALID_OWD = (1 << 1),
55	LP_WITHIN_THR = (1 << 3),
56	LP_WITHIN_INF = (1 << 4),
57};
58
59/**
60 * struct lp
61 * @flag: TCP-LP state flag
62 * @sowd: smoothed OWD << 3
63 * @owd_min: min OWD
64 * @owd_max: max OWD
65 * @owd_max_rsv: resrved max owd
66 * @remote_hz: estimated remote HZ
67 * @remote_ref_time: remote reference time
68 * @local_ref_time: local reference time
69 * @last_drop: time for last active drop
70 * @inference: current inference
71 *
72 * TCP-LP's private struct.
73 * We get the idea from original TCP-LP implementation where only left those we
74 * found are really useful.
75 */
76struct lp {
77	u32 flag;
78	u32 sowd;
79	u32 owd_min;
80	u32 owd_max;
81	u32 owd_max_rsv;
82	u32 remote_hz;
83	u32 remote_ref_time;
84	u32 local_ref_time;
85	u32 last_drop;
86	u32 inference;
87};
88
89/**
90 * tcp_lp_init
91 *
92 * Init all required variables.
93 * Clone the handling from Vegas module implementation.
94 */
95static void tcp_lp_init(struct sock *sk)
96{
97	struct lp *lp = inet_csk_ca(sk);
98
99	lp->flag = 0;
100	lp->sowd = 0;
101	lp->owd_min = 0xffffffff;
102	lp->owd_max = 0;
103	lp->owd_max_rsv = 0;
104	lp->remote_hz = 0;
105	lp->remote_ref_time = 0;
106	lp->local_ref_time = 0;
107	lp->last_drop = 0;
108	lp->inference = 0;
109}
110
111/**
112 * tcp_lp_cong_avoid
113 *
114 * Implementation of cong_avoid.
115 * Will only call newReno CA when away from inference.
116 * From TCP-LP's paper, this will be handled in additive increasement.
117 */
118static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
119{
120	struct lp *lp = inet_csk_ca(sk);
121
122	if (!(lp->flag & LP_WITHIN_INF))
123		tcp_reno_cong_avoid(sk, ack, acked);
124}
125
126/**
127 * tcp_lp_remote_hz_estimator
128 *
129 * Estimate remote HZ.
130 * We keep on updating the estimated value, where original TCP-LP
131 * implementation only guest it for once and use forever.
132 */
133static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
134{
135	struct tcp_sock *tp = tcp_sk(sk);
136	struct lp *lp = inet_csk_ca(sk);
137	s64 rhz = lp->remote_hz << 6;	/* remote HZ << 6 */
138	s64 m = 0;
139
140	/* not yet record reference time
141	 * go away!! record it before come back!! */
142	if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
143		goto out;
144
145	/* we can't calc remote HZ with no different!! */
146	if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||
147	    tp->rx_opt.rcv_tsecr == lp->local_ref_time)
148		goto out;
149
150	m = HZ * (tp->rx_opt.rcv_tsval -
151		  lp->remote_ref_time) / (tp->rx_opt.rcv_tsecr -
152					  lp->local_ref_time);
153	if (m < 0)
154		m = -m;
155
156	if (rhz > 0) {
157		m -= rhz >> 6;	/* m is now error in remote HZ est */
158		rhz += m;	/* 63/64 old + 1/64 new */
159	} else
160		rhz = m << 6;
161
162 out:
163	/* record time for successful remote HZ calc */
164	if ((rhz >> 6) > 0)
165		lp->flag |= LP_VALID_RHZ;
166	else
167		lp->flag &= ~LP_VALID_RHZ;
168
169	/* record reference time stamp */
170	lp->remote_ref_time = tp->rx_opt.rcv_tsval;
171	lp->local_ref_time = tp->rx_opt.rcv_tsecr;
172
173	return rhz >> 6;
174}
175
176/**
177 * tcp_lp_owd_calculator
178 *
179 * Calculate one way delay (in relative format).
180 * Original implement OWD as minus of remote time difference to local time
181 * difference directly. As this time difference just simply equal to RTT, when
182 * the network status is stable, remote RTT will equal to local RTT, and result
183 * OWD into zero.
184 * It seems to be a bug and so we fixed it.
185 */
186static u32 tcp_lp_owd_calculator(struct sock *sk)
187{
188	struct tcp_sock *tp = tcp_sk(sk);
189	struct lp *lp = inet_csk_ca(sk);
190	s64 owd = 0;
191
192	lp->remote_hz = tcp_lp_remote_hz_estimator(sk);
193
194	if (lp->flag & LP_VALID_RHZ) {
195		owd =
196		    tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
197		    tp->rx_opt.rcv_tsecr * (LP_RESOL / HZ);
198		if (owd < 0)
199			owd = -owd;
200	}
201
202	if (owd > 0)
203		lp->flag |= LP_VALID_OWD;
204	else
205		lp->flag &= ~LP_VALID_OWD;
206
207	return owd;
208}
209
210/**
211 * tcp_lp_rtt_sample
212 *
213 * Implementation or rtt_sample.
214 * Will take the following action,
215 *   1. calc OWD,
216 *   2. record the min/max OWD,
217 *   3. calc smoothed OWD (SOWD).
218 * Most ideas come from the original TCP-LP implementation.
219 */
220static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt)
221{
222	struct lp *lp = inet_csk_ca(sk);
223	s64 mowd = tcp_lp_owd_calculator(sk);
224
225	/* sorry that we don't have valid data */
226	if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))
227		return;
228
229	/* record the next min owd */
230	if (mowd < lp->owd_min)
231		lp->owd_min = mowd;
232
233	/* always forget the max of the max
234	 * we just set owd_max as one below it */
235	if (mowd > lp->owd_max) {
236		if (mowd > lp->owd_max_rsv) {
237			if (lp->owd_max_rsv == 0)
238				lp->owd_max = mowd;
239			else
240				lp->owd_max = lp->owd_max_rsv;
241			lp->owd_max_rsv = mowd;
242		} else
243			lp->owd_max = mowd;
244	}
245
246	/* calc for smoothed owd */
247	if (lp->sowd != 0) {
248		mowd -= lp->sowd >> 3;	/* m is now error in owd est */
249		lp->sowd += mowd;	/* owd = 7/8 owd + 1/8 new */
250	} else
251		lp->sowd = mowd << 3;	/* take the measured time be owd */
252}
253
254/**
255 * tcp_lp_pkts_acked
256 *
257 * Implementation of pkts_acked.
258 * Deal with active drop under Early Congestion Indication.
259 * Only drop to half and 1 will be handle, because we hope to use back
260 * newReno in increase case.
261 * We work it out by following the idea from TCP-LP's paper directly
262 */
263static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked, s32 rtt_us)
264{
265	struct tcp_sock *tp = tcp_sk(sk);
266	struct lp *lp = inet_csk_ca(sk);
267
268	if (rtt_us > 0)
269		tcp_lp_rtt_sample(sk, rtt_us);
270
271	/* calc inference */
272	if (tcp_time_stamp > tp->rx_opt.rcv_tsecr)
273		lp->inference = 3 * (tcp_time_stamp - tp->rx_opt.rcv_tsecr);
274
275	/* test if within inference */
276	if (lp->last_drop && (tcp_time_stamp - lp->last_drop < lp->inference))
277		lp->flag |= LP_WITHIN_INF;
278	else
279		lp->flag &= ~LP_WITHIN_INF;
280
281	/* test if within threshold */
282	if (lp->sowd >> 3 <
283	    lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)
284		lp->flag |= LP_WITHIN_THR;
285	else
286		lp->flag &= ~LP_WITHIN_THR;
287
288	pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,
289		 tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,
290		 lp->sowd >> 3);
291
292	if (lp->flag & LP_WITHIN_THR)
293		return;
294
295	/* FIXME: try to reset owd_min and owd_max here
296	 * so decrease the chance the min/max is no longer suitable
297	 * and will usually within threshold when whithin inference */
298	lp->owd_min = lp->sowd >> 3;
299	lp->owd_max = lp->sowd >> 2;
300	lp->owd_max_rsv = lp->sowd >> 2;
301
302	/* happened within inference
303	 * drop snd_cwnd into 1 */
304	if (lp->flag & LP_WITHIN_INF)
305		tp->snd_cwnd = 1U;
306
307	/* happened after inference
308	 * cut snd_cwnd into half */
309	else
310		tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);
311
312	/* record this drop time */
313	lp->last_drop = tcp_time_stamp;
314}
315
316static struct tcp_congestion_ops tcp_lp __read_mostly = {
317	.init = tcp_lp_init,
318	.ssthresh = tcp_reno_ssthresh,
319	.cong_avoid = tcp_lp_cong_avoid,
320	.pkts_acked = tcp_lp_pkts_acked,
321
322	.owner = THIS_MODULE,
323	.name = "lp"
324};
325
326static int __init tcp_lp_register(void)
327{
328	BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE);
329	return tcp_register_congestion_control(&tcp_lp);
330}
331
332static void __exit tcp_lp_unregister(void)
333{
334	tcp_unregister_congestion_control(&tcp_lp);
335}
336
337module_init(tcp_lp_register);
338module_exit(tcp_lp_unregister);
339
340MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
341MODULE_LICENSE("GPL");
342MODULE_DESCRIPTION("TCP Low Priority");
343