1 // SPDX-License-Identifier: GPL-2.0-only
3  * CAIA Delay-Gradient (CDG) congestion control
7  *   delay gradients." In IFIP Networking, pages 328-341. Springer, 2011.
9  * Scavenger traffic (Less-than-Best-Effort) should disable coexistence
10  * heuristics using parameters use_shadow=0 and use_ineff=0.
22  *   o Add toggle for non-congestion loss tolerance.
26  *   o More accurate e^-x.
49 MODULE_PARM_DESC(backoff_beta, "backoff beta (0-1024)");
54 		 "(0: disabled, 1: ACK train, 2: delay threshold, 3: both)");
73 	CDG_UNKNOWN = 0,
98  * nexp_u32 - negative base-e exponential
101  * Returns exp(ux * -1e-6) * U32_MAX.
106 		/* exp(-x)*65536-1 for x = 0, 0.000256, 0.000512, ... */  in nexp_u32()
109 		61378, 57484, 50423, 38795, 22965, 8047,  987,   14,  in nexp_u32()
117 		return 0;  in nexp_u32()
120 	res = U32_MAX - (ux & 0xff) * (U32_MAX / 1000000);  in nexp_u32()
124 		u32 y = v[i & -(msb & 1)] + U32_C(1);  in nexp_u32()
145 	ca->delay_min = min_not_zero(ca->delay_min, ca->rtt.min);  in tcp_cdg_hystart_update()
146 	if (ca->delay_min == 0)  in tcp_cdg_hystart_update()
150 		u32 now_us = tp->tcp_mstamp;  in tcp_cdg_hystart_update()
152 		if (ca->last_ack == 0 || !tcp_is_cwnd_limited(sk)) {  in tcp_cdg_hystart_update()
153 			ca->last_ack = now_us;  in tcp_cdg_hystart_update()
154 			ca->round_start = now_us;  in tcp_cdg_hystart_update()
155 		} else if (before(now_us, ca->last_ack + 3000)) {  in tcp_cdg_hystart_update()
156 			u32 base_owd = max(ca->delay_min / 2U, 125U);  in tcp_cdg_hystart_update()
158 			ca->last_ack = now_us;  in tcp_cdg_hystart_update()
159 			if (after(now_us, ca->round_start + base_owd)) {  in tcp_cdg_hystart_update()
164 					      tp->snd_cwnd);  in tcp_cdg_hystart_update()
165 				tp->snd_ssthresh = tp->snd_cwnd;  in tcp_cdg_hystart_update()
172 		if (ca->sample_cnt < 8) {  in tcp_cdg_hystart_update()
173 			ca->sample_cnt++;  in tcp_cdg_hystart_update()
175 			s32 thresh = max(ca->delay_min + ca->delay_min / 8U,  in tcp_cdg_hystart_update()
178 			if (ca->rtt.min > thresh) {  in tcp_cdg_hystart_update()
183 					      tp->snd_cwnd);  in tcp_cdg_hystart_update()
184 				tp->snd_ssthresh = tp->snd_cwnd;  in tcp_cdg_hystart_update()
192 	s32 gmin = ca->rtt.min - ca->rtt_prev.min;  in tcp_cdg_grad()
193 	s32 gmax = ca->rtt.max - ca->rtt_prev.max;  in tcp_cdg_grad()
196 	if (ca->gradients) {  in tcp_cdg_grad()
197 		ca->gsum.min += gmin - ca->gradients[ca->tail].min;  in tcp_cdg_grad()
198 		ca->gsum.max += gmax - ca->gradients[ca->tail].max;  in tcp_cdg_grad()
199 		ca->gradients[ca->tail].min = gmin;  in tcp_cdg_grad()
200 		ca->gradients[ca->tail].max = gmax;  in tcp_cdg_grad()
201 		ca->tail = (ca->tail + 1) & (window - 1);  in tcp_cdg_grad()
202 		gmin = ca->gsum.min;  in tcp_cdg_grad()
203 		gmax = ca->gsum.max;  in tcp_cdg_grad()
208 	 * (rtt_latest - rtt_oldest) / window.  in tcp_cdg_grad()
212 	grad = gmin > 0 ? gmin : gmax;  in tcp_cdg_grad()
215 	if (!ca->gfilled) {  in tcp_cdg_grad()
216 		if (!ca->gradients && window > 1)  in tcp_cdg_grad()
218 		else if (ca->tail == 0)  in tcp_cdg_grad()
219 			ca->gfilled = true;  in tcp_cdg_grad()
221 			grad = (grad * window) / (int)ca->tail;  in tcp_cdg_grad()
225 	if (gmin <= -32 || gmax <= -32)  in tcp_cdg_grad()
226 		ca->backoff_cnt = 0;  in tcp_cdg_grad()
233 		if (gmin > 0 && gmax <= 0)  in tcp_cdg_grad()
234 			ca->state = CDG_FULL;  in tcp_cdg_grad()
235 		else if ((gmin > 0 && gmax > 0) || gmax < 0)  in tcp_cdg_grad()
236 			ca->state = CDG_NONFULL;  in tcp_cdg_grad()
250 		ca->backoff_cnt++;  in tcp_cdg_backoff()
251 		if (ca->backoff_cnt > use_ineff)  in tcp_cdg_backoff()
255 	ca->shadow_wnd = max(ca->shadow_wnd, tp->snd_cwnd);  in tcp_cdg_backoff()
256 	ca->state = CDG_BACKOFF;  in tcp_cdg_backoff()
272 	if (after(ack, ca->rtt_seq) && ca->rtt.v64) {  in tcp_cdg_cong_avoid()
273 		s32 grad = 0;  in tcp_cdg_cong_avoid()
275 		if (ca->rtt_prev.v64)  in tcp_cdg_cong_avoid()
277 		ca->rtt_seq = tp->snd_nxt;  in tcp_cdg_cong_avoid()
278 		ca->rtt_prev = ca->rtt;  in tcp_cdg_cong_avoid()
279 		ca->rtt.v64 = 0;  in tcp_cdg_cong_avoid()
280 		ca->last_ack = 0;  in tcp_cdg_cong_avoid()
281 		ca->sample_cnt = 0;  in tcp_cdg_cong_avoid()
283 		if (grad > 0 && tcp_cdg_backoff(sk, grad))  in tcp_cdg_cong_avoid()
288 		ca->shadow_wnd = min(ca->shadow_wnd, tp->snd_cwnd);  in tcp_cdg_cong_avoid()
292 	prior_snd_cwnd = tp->snd_cwnd;  in tcp_cdg_cong_avoid()
295 	incr = tp->snd_cwnd - prior_snd_cwnd;  in tcp_cdg_cong_avoid()
296 	ca->shadow_wnd = max(ca->shadow_wnd, ca->shadow_wnd + incr);  in tcp_cdg_cong_avoid()
304 	if (sample->rtt_us <= 0)  in tcp_cdg_acked()
311 	if (tp->sacked_out == 0) {  in tcp_cdg_acked()
312 		if (sample->pkts_acked == 1 && ca->delack) {  in tcp_cdg_acked()
314 			 * provenly lower than an existing non-zero minimum.  in tcp_cdg_acked()
316 			ca->rtt.min = min(ca->rtt.min, sample->rtt_us);  in tcp_cdg_acked()
317 			ca->delack--;  in tcp_cdg_acked()
319 		} else if (sample->pkts_acked > 1 && ca->delack < 5) {  in tcp_cdg_acked()
320 			ca->delack++;  in tcp_cdg_acked()
324 	ca->rtt.min = min_not_zero(ca->rtt.min, sample->rtt_us);  in tcp_cdg_acked()
325 	ca->rtt.max = max(ca->rtt.max, sample->rtt_us);  in tcp_cdg_acked()
333 	if (ca->state == CDG_BACKOFF)  in tcp_cdg_ssthresh()
334 		return max(2U, (tp->snd_cwnd * min(1024U, backoff_beta)) >> 10);  in tcp_cdg_ssthresh()
336 	if (ca->state == CDG_NONFULL && use_tolerance)  in tcp_cdg_ssthresh()
337 		return tp->snd_cwnd;  in tcp_cdg_ssthresh()
339 	ca->shadow_wnd = min(ca->shadow_wnd >> 1, tp->snd_cwnd);  in tcp_cdg_ssthresh()
341 		return max3(2U, ca->shadow_wnd, tp->snd_cwnd >> 1);  in tcp_cdg_ssthresh()
342 	return max(2U, tp->snd_cwnd >> 1);  in tcp_cdg_ssthresh()
353 		gradients = ca->gradients;  in tcp_cdg_cwnd_event()
355 			memset(gradients, 0, window * sizeof(gradients[0]));  in tcp_cdg_cwnd_event()
356 		memset(ca, 0, sizeof(*ca));  in tcp_cdg_cwnd_event()
358 		ca->gradients = gradients;  in tcp_cdg_cwnd_event()
359 		ca->rtt_seq = tp->snd_nxt;  in tcp_cdg_cwnd_event()
360 		ca->shadow_wnd = tp->snd_cwnd;  in tcp_cdg_cwnd_event()
363 		ca->state = CDG_UNKNOWN;  in tcp_cdg_cwnd_event()
364 		ca->rtt_seq = tp->snd_nxt;  in tcp_cdg_cwnd_event()
365 		ca->rtt_prev = ca->rtt;  in tcp_cdg_cwnd_event()
366 		ca->rtt.v64 = 0;  in tcp_cdg_cwnd_event()
380 		ca->gradients = kcalloc(window, sizeof(ca->gradients[0]),  in tcp_cdg_init()
382 	ca->rtt_seq = tp->snd_nxt;  in tcp_cdg_init()
383 	ca->shadow_wnd = tp->snd_cwnd;  in tcp_cdg_init()
390 	kfree(ca->gradients);  in tcp_cdg_release()
408 		return -ERANGE;  in tcp_cdg_register()
410 		return -EINVAL;  in tcp_cdg_register()
414 	return 0;  in tcp_cdg_register()