1#ifndef __NET_SCHED_CODEL_IMPL_H
2#define __NET_SCHED_CODEL_IMPL_H
3
4/*
5 * Codel - The Controlled-Delay Active Queue Management algorithm
6 *
7 *  Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
8 *  Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
9 *  Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
10 *  Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 *    notice, this list of conditions, and the following disclaimer,
17 *    without modification.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 *    notice, this list of conditions and the following disclaimer in the
20 *    documentation and/or other materials provided with the distribution.
21 * 3. The names of the authors may not be used to endorse or promote products
22 *    derived from this software without specific prior written permission.
23 *
24 * Alternatively, provided that this notice is retained in full, this
25 * software may be distributed under the terms of the GNU General
26 * Public License ("GPL") version 2, in which case the provisions of the
27 * GPL apply INSTEAD OF those given above.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
30 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
31 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
32 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
33 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
34 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
36 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
37 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
38 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
39 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
40 * DAMAGE.
41 *
42 */
43
44/* Controlling Queue Delay (CoDel) algorithm
45 * =========================================
46 * Source : Kathleen Nichols and Van Jacobson
47 * http://queue.acm.org/detail.cfm?id=2209336
48 *
49 * Implemented on linux by Dave Taht and Eric Dumazet
50 */
51
52#include <net/inet_ecn.h>
53
54static void codel_params_init(struct codel_params *params)
55{
56	params->interval = MS2TIME(100);
57	params->target = MS2TIME(5);
58	params->ce_threshold = CODEL_DISABLED_THRESHOLD;
59	params->ce_threshold_mask = 0;
60	params->ce_threshold_selector = 0;
61	params->ecn = false;
62}
63
64static void codel_vars_init(struct codel_vars *vars)
65{
66	memset(vars, 0, sizeof(*vars));
67}
68
69static void codel_stats_init(struct codel_stats *stats)
70{
71	stats->maxpacket = 0;
72}
73
74/*
75 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
76 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
77 *
78 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
79 */
80static void codel_Newton_step(struct codel_vars *vars)
81{
82	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
83	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
84	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
85
86	val >>= 2; /* avoid overflow in following multiply */
87	val = (val * invsqrt) >> (32 - 2 + 1);
88
89	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
90}
91
92/*
93 * CoDel control_law is t + interval/sqrt(count)
94 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
95 * both sqrt() and divide operation.
96 */
97static codel_time_t codel_control_law(codel_time_t t,
98				      codel_time_t interval,
99				      u32 rec_inv_sqrt)
100{
101	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
102}
103
104static bool codel_should_drop(const struct sk_buff *skb,
105			      void *ctx,
106			      struct codel_vars *vars,
107			      struct codel_params *params,
108			      struct codel_stats *stats,
109			      codel_skb_len_t skb_len_func,
110			      codel_skb_time_t skb_time_func,
111			      u32 *backlog,
112			      codel_time_t now)
113{
114	bool ok_to_drop;
115	u32 skb_len;
116
117	if (!skb) {
118		vars->first_above_time = 0;
119		return false;
120	}
121
122	skb_len = skb_len_func(skb);
123	vars->ldelay = now - skb_time_func(skb);
124
125	if (unlikely(skb_len > stats->maxpacket))
126		stats->maxpacket = skb_len;
127
128	if (codel_time_before(vars->ldelay, params->target) ||
129	    *backlog <= params->mtu) {
130		/* went below - stay below for at least interval */
131		vars->first_above_time = 0;
132		return false;
133	}
134	ok_to_drop = false;
135	if (vars->first_above_time == 0) {
136		/* just went above from below. If we stay above
137		 * for at least interval we'll say it's ok to drop
138		 */
139		vars->first_above_time = now + params->interval;
140	} else if (codel_time_after(now, vars->first_above_time)) {
141		ok_to_drop = true;
142	}
143	return ok_to_drop;
144}
145
146static struct sk_buff *codel_dequeue(void *ctx,
147				     u32 *backlog,
148				     struct codel_params *params,
149				     struct codel_vars *vars,
150				     struct codel_stats *stats,
151				     codel_skb_len_t skb_len_func,
152				     codel_skb_time_t skb_time_func,
153				     codel_skb_drop_t drop_func,
154				     codel_skb_dequeue_t dequeue_func)
155{
156	struct sk_buff *skb = dequeue_func(vars, ctx);
157	codel_time_t now;
158	bool drop;
159
160	if (!skb) {
161		vars->dropping = false;
162		return skb;
163	}
164	now = codel_get_time();
165	drop = codel_should_drop(skb, ctx, vars, params, stats,
166				 skb_len_func, skb_time_func, backlog, now);
167	if (vars->dropping) {
168		if (!drop) {
169			/* sojourn time below target - leave dropping state */
170			vars->dropping = false;
171		} else if (codel_time_after_eq(now, vars->drop_next)) {
172			/* It's time for the next drop. Drop the current
173			 * packet and dequeue the next. The dequeue might
174			 * take us out of dropping state.
175			 * If not, schedule the next drop.
176			 * A large backlog might result in drop rates so high
177			 * that the next drop should happen now,
178			 * hence the while loop.
179			 */
180			while (vars->dropping &&
181			       codel_time_after_eq(now, vars->drop_next)) {
182				vars->count++; /* dont care of possible wrap
183						* since there is no more divide
184						*/
185				codel_Newton_step(vars);
186				if (params->ecn && INET_ECN_set_ce(skb)) {
187					stats->ecn_mark++;
188					vars->drop_next =
189						codel_control_law(vars->drop_next,
190								  params->interval,
191								  vars->rec_inv_sqrt);
192					goto end;
193				}
194				stats->drop_len += skb_len_func(skb);
195				drop_func(skb, ctx);
196				stats->drop_count++;
197				skb = dequeue_func(vars, ctx);
198				if (!codel_should_drop(skb, ctx,
199						       vars, params, stats,
200						       skb_len_func,
201						       skb_time_func,
202						       backlog, now)) {
203					/* leave dropping state */
204					vars->dropping = false;
205				} else {
206					/* and schedule the next drop */
207					vars->drop_next =
208						codel_control_law(vars->drop_next,
209								  params->interval,
210								  vars->rec_inv_sqrt);
211				}
212			}
213		}
214	} else if (drop) {
215		u32 delta;
216
217		if (params->ecn && INET_ECN_set_ce(skb)) {
218			stats->ecn_mark++;
219		} else {
220			stats->drop_len += skb_len_func(skb);
221			drop_func(skb, ctx);
222			stats->drop_count++;
223
224			skb = dequeue_func(vars, ctx);
225			drop = codel_should_drop(skb, ctx, vars, params,
226						 stats, skb_len_func,
227						 skb_time_func, backlog, now);
228		}
229		vars->dropping = true;
230		/* if min went above target close to when we last went below it
231		 * assume that the drop rate that controlled the queue on the
232		 * last cycle is a good starting point to control it now.
233		 */
234		delta = vars->count - vars->lastcount;
235		if (delta > 1 &&
236		    codel_time_before(now - vars->drop_next,
237				      16 * params->interval)) {
238			vars->count = delta;
239			/* we dont care if rec_inv_sqrt approximation
240			 * is not very precise :
241			 * Next Newton steps will correct it quadratically.
242			 */
243			codel_Newton_step(vars);
244		} else {
245			vars->count = 1;
246			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
247		}
248		vars->lastcount = vars->count;
249		vars->drop_next = codel_control_law(now, params->interval,
250						    vars->rec_inv_sqrt);
251	}
252end:
253	if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
254		bool set_ce = true;
255
256		if (params->ce_threshold_mask) {
257			int dsfield = skb_get_dsfield(skb);
258
259			set_ce = (dsfield >= 0 &&
260				  (((u8)dsfield & params->ce_threshold_mask) ==
261				   params->ce_threshold_selector));
262		}
263		if (set_ce && INET_ECN_set_ce(skb))
264			stats->ce_mark++;
265	}
266	return skb;
267}
268
269#endif
270