1 // SPDX-License-Identifier: GPL-2.0-only
3  * TCP Low Priority (TCP-LP)
11  * the original TCP-LP implementation:
16  *   o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since
20  *   o OWD is handled in relative format, where local time stamp will in
26  *   http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf
28  *   http://www-ece.rice.edu/networks/TCP-LP/
34  *   http://tcp-lp-mod.sourceforge.net/
50  * TCP-LP's state flags.
62  * @flag: TCP-LP state flag
64  * @owd_min: min OWD
68  * @remote_ref_time: remote reference time
69  * @local_ref_time: local reference time
70  * @last_drop: time for last active drop
73  * TCP-LP's private struct.
74  * We get the idea from original TCP-LP implementation where only left those we
100 	lp->flag = 0;  in tcp_lp_init()
101 	lp->sowd = 0;  in tcp_lp_init()
102 	lp->owd_min = 0xffffffff;  in tcp_lp_init()
103 	lp->owd_max = 0;  in tcp_lp_init()
104 	lp->owd_max_rsv = 0;  in tcp_lp_init()
105 	lp->remote_hz = 0;  in tcp_lp_init()
106 	lp->remote_ref_time = 0;  in tcp_lp_init()
107 	lp->local_ref_time = 0;  in tcp_lp_init()
108 	lp->last_drop = 0;  in tcp_lp_init()
109 	lp->inference = 0;  in tcp_lp_init()
117  * From TCP-LP's paper, this will be handled in additive increasement.
123 	if (!(lp->flag & LP_WITHIN_INF))  in tcp_lp_cong_avoid()
131  * We keep on updating the estimated value, where original TCP-LP
138 	s64 rhz = lp->remote_hz << 6;	/* remote HZ << 6 */  in tcp_lp_remote_hz_estimator()
141 	/* not yet record reference time  in tcp_lp_remote_hz_estimator()
143 	if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)  in tcp_lp_remote_hz_estimator()
147 	if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||  in tcp_lp_remote_hz_estimator()
148 	    tp->rx_opt.rcv_tsecr == lp->local_ref_time)  in tcp_lp_remote_hz_estimator()
152 	    (tp->rx_opt.rcv_tsval - lp->remote_ref_time) /  in tcp_lp_remote_hz_estimator()
153 	    (tp->rx_opt.rcv_tsecr - lp->local_ref_time);  in tcp_lp_remote_hz_estimator()
155 		m = -m;  in tcp_lp_remote_hz_estimator()
158 		m -= rhz >> 6;	/* m is now error in remote HZ est */  in tcp_lp_remote_hz_estimator()
164 	/* record time for successful remote HZ calc */  in tcp_lp_remote_hz_estimator()
166 		lp->flag |= LP_VALID_RHZ;  in tcp_lp_remote_hz_estimator()
168 		lp->flag &= ~LP_VALID_RHZ;  in tcp_lp_remote_hz_estimator()
170 	/* record reference time stamp */  in tcp_lp_remote_hz_estimator()
171 	lp->remote_ref_time = tp->rx_opt.rcv_tsval;  in tcp_lp_remote_hz_estimator()
172 	lp->local_ref_time = tp->rx_opt.rcv_tsecr;  in tcp_lp_remote_hz_estimator()
181  * Original implement OWD as minus of remote time difference to local time
182  * difference directly. As this time difference just simply equal to RTT, when
193 	lp->remote_hz = tcp_lp_remote_hz_estimator(sk);  in tcp_lp_owd_calculator()
195 	if (lp->flag & LP_VALID_RHZ) {  in tcp_lp_owd_calculator()
197 		    tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -  in tcp_lp_owd_calculator()
198 		    tp->rx_opt.rcv_tsecr * (LP_RESOL / TCP_TS_HZ);  in tcp_lp_owd_calculator()
200 			owd = -owd;  in tcp_lp_owd_calculator()
204 		lp->flag |= LP_VALID_OWD;  in tcp_lp_owd_calculator()
206 		lp->flag &= ~LP_VALID_OWD;  in tcp_lp_owd_calculator()
217  *   2. record the min/max OWD,
219  * Most ideas come from the original TCP-LP implementation.
227 	if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))  in tcp_lp_rtt_sample()
230 	/* record the next min owd */  in tcp_lp_rtt_sample()
231 	if (mowd < lp->owd_min)  in tcp_lp_rtt_sample()
232 		lp->owd_min = mowd;  in tcp_lp_rtt_sample()
236 	if (mowd > lp->owd_max) {  in tcp_lp_rtt_sample()
237 		if (mowd > lp->owd_max_rsv) {  in tcp_lp_rtt_sample()
238 			if (lp->owd_max_rsv == 0)  in tcp_lp_rtt_sample()
239 				lp->owd_max = mowd;  in tcp_lp_rtt_sample()
241 				lp->owd_max = lp->owd_max_rsv;  in tcp_lp_rtt_sample()
242 			lp->owd_max_rsv = mowd;  in tcp_lp_rtt_sample()
244 			lp->owd_max = mowd;  in tcp_lp_rtt_sample()
248 	if (lp->sowd != 0) {  in tcp_lp_rtt_sample()
249 		mowd -= lp->sowd >> 3;	/* m is now error in owd est */  in tcp_lp_rtt_sample()
250 		lp->sowd += mowd;	/* owd = 7/8 owd + 1/8 new */  in tcp_lp_rtt_sample()
252 		lp->sowd = mowd << 3;	/* take the measured time be owd */  in tcp_lp_rtt_sample()
262  * We work it out by following the idea from TCP-LP's paper directly
264 static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample)  in tcp_lp_pkts_acked()  argument
271 	if (sample->rtt_us > 0)  in tcp_lp_pkts_acked()
272 		tcp_lp_rtt_sample(sk, sample->rtt_us);  in tcp_lp_pkts_acked()
275 	delta = now - tp->rx_opt.rcv_tsecr;  in tcp_lp_pkts_acked()
277 		lp->inference = 3 * delta;  in tcp_lp_pkts_acked()
280 	if (lp->last_drop && (now - lp->last_drop < lp->inference))  in tcp_lp_pkts_acked()
281 		lp->flag |= LP_WITHIN_INF;  in tcp_lp_pkts_acked()
283 		lp->flag &= ~LP_WITHIN_INF;  in tcp_lp_pkts_acked()
286 	if (lp->sowd >> 3 <  in tcp_lp_pkts_acked()
287 	    lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)  in tcp_lp_pkts_acked()
288 		lp->flag |= LP_WITHIN_THR;  in tcp_lp_pkts_acked()
290 		lp->flag &= ~LP_WITHIN_THR;  in tcp_lp_pkts_acked()
292 	pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,  in tcp_lp_pkts_acked()
293 		 tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,  in tcp_lp_pkts_acked()
294 		 lp->sowd >> 3);  in tcp_lp_pkts_acked()
296 	if (lp->flag & LP_WITHIN_THR)  in tcp_lp_pkts_acked()
300 	 * so decrease the chance the min/max is no longer suitable  in tcp_lp_pkts_acked()
302 	lp->owd_min = lp->sowd >> 3;  in tcp_lp_pkts_acked()
303 	lp->owd_max = lp->sowd >> 2;  in tcp_lp_pkts_acked()
304 	lp->owd_max_rsv = lp->sowd >> 2;  in tcp_lp_pkts_acked()
308 	if (lp->flag & LP_WITHIN_INF)  in tcp_lp_pkts_acked()
309 		tp->snd_cwnd = 1U;  in tcp_lp_pkts_acked()
314 		tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);  in tcp_lp_pkts_acked()
316 	/* record this drop time */  in tcp_lp_pkts_acked()
317 	lp->last_drop = now;  in tcp_lp_pkts_acked()