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 
codel_params_init(struct codel_params * params)52 static void codel_params_init(struct codel_params *params)
53 {
54 	params->interval = MS2TIME(100);
55 	params->target = MS2TIME(5);
56 	params->ce_threshold = CODEL_DISABLED_THRESHOLD;
57 	params->ecn = false;
58 }
59 
codel_vars_init(struct codel_vars * vars)60 static void codel_vars_init(struct codel_vars *vars)
61 {
62 	memset(vars, 0, sizeof(*vars));
63 }
64 
codel_stats_init(struct codel_stats * stats)65 static void codel_stats_init(struct codel_stats *stats)
66 {
67 	stats->maxpacket = 0;
68 }
69 
70 /*
71  * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
72  * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
73  *
74  * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
75  */
codel_Newton_step(struct codel_vars * vars)76 static void codel_Newton_step(struct codel_vars *vars)
77 {
78 	u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
79 	u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
80 	u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
81 
82 	val >>= 2; /* avoid overflow in following multiply */
83 	val = (val * invsqrt) >> (32 - 2 + 1);
84 
85 	vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
86 }
87 
88 /*
89  * CoDel control_law is t + interval/sqrt(count)
90  * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
91  * both sqrt() and divide operation.
92  */
codel_control_law(codel_time_t t,codel_time_t interval,u32 rec_inv_sqrt)93 static codel_time_t codel_control_law(codel_time_t t,
94 				      codel_time_t interval,
95 				      u32 rec_inv_sqrt)
96 {
97 	return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
98 }
99 
codel_should_drop(const struct sk_buff * skb,void * ctx,struct codel_vars * vars,struct codel_params * params,struct codel_stats * stats,codel_skb_len_t skb_len_func,codel_skb_time_t skb_time_func,u32 * backlog,codel_time_t now)100 static bool codel_should_drop(const struct sk_buff *skb,
101 			      void *ctx,
102 			      struct codel_vars *vars,
103 			      struct codel_params *params,
104 			      struct codel_stats *stats,
105 			      codel_skb_len_t skb_len_func,
106 			      codel_skb_time_t skb_time_func,
107 			      u32 *backlog,
108 			      codel_time_t now)
109 {
110 	bool ok_to_drop;
111 	u32 skb_len;
112 
113 	if (!skb) {
114 		vars->first_above_time = 0;
115 		return false;
116 	}
117 
118 	skb_len = skb_len_func(skb);
119 	vars->ldelay = now - skb_time_func(skb);
120 
121 	if (unlikely(skb_len > stats->maxpacket))
122 		stats->maxpacket = skb_len;
123 
124 	if (codel_time_before(vars->ldelay, params->target) ||
125 	    *backlog <= params->mtu) {
126 		/* went below - stay below for at least interval */
127 		vars->first_above_time = 0;
128 		return false;
129 	}
130 	ok_to_drop = false;
131 	if (vars->first_above_time == 0) {
132 		/* just went above from below. If we stay above
133 		 * for at least interval we'll say it's ok to drop
134 		 */
135 		vars->first_above_time = now + params->interval;
136 	} else if (codel_time_after(now, vars->first_above_time)) {
137 		ok_to_drop = true;
138 	}
139 	return ok_to_drop;
140 }
141 
codel_dequeue(void * ctx,u32 * backlog,struct codel_params * params,struct codel_vars * vars,struct codel_stats * stats,codel_skb_len_t skb_len_func,codel_skb_time_t skb_time_func,codel_skb_drop_t drop_func,codel_skb_dequeue_t dequeue_func)142 static struct sk_buff *codel_dequeue(void *ctx,
143 				     u32 *backlog,
144 				     struct codel_params *params,
145 				     struct codel_vars *vars,
146 				     struct codel_stats *stats,
147 				     codel_skb_len_t skb_len_func,
148 				     codel_skb_time_t skb_time_func,
149 				     codel_skb_drop_t drop_func,
150 				     codel_skb_dequeue_t dequeue_func)
151 {
152 	struct sk_buff *skb = dequeue_func(vars, ctx);
153 	codel_time_t now;
154 	bool drop;
155 
156 	if (!skb) {
157 		vars->dropping = false;
158 		return skb;
159 	}
160 	now = codel_get_time();
161 	drop = codel_should_drop(skb, ctx, vars, params, stats,
162 				 skb_len_func, skb_time_func, backlog, now);
163 	if (vars->dropping) {
164 		if (!drop) {
165 			/* sojourn time below target - leave dropping state */
166 			vars->dropping = false;
167 		} else if (codel_time_after_eq(now, vars->drop_next)) {
168 			/* It's time for the next drop. Drop the current
169 			 * packet and dequeue the next. The dequeue might
170 			 * take us out of dropping state.
171 			 * If not, schedule the next drop.
172 			 * A large backlog might result in drop rates so high
173 			 * that the next drop should happen now,
174 			 * hence the while loop.
175 			 */
176 			while (vars->dropping &&
177 			       codel_time_after_eq(now, vars->drop_next)) {
178 				vars->count++; /* dont care of possible wrap
179 						* since there is no more divide
180 						*/
181 				codel_Newton_step(vars);
182 				if (params->ecn && INET_ECN_set_ce(skb)) {
183 					stats->ecn_mark++;
184 					vars->drop_next =
185 						codel_control_law(vars->drop_next,
186 								  params->interval,
187 								  vars->rec_inv_sqrt);
188 					goto end;
189 				}
190 				stats->drop_len += skb_len_func(skb);
191 				drop_func(skb, ctx);
192 				stats->drop_count++;
193 				skb = dequeue_func(vars, ctx);
194 				if (!codel_should_drop(skb, ctx,
195 						       vars, params, stats,
196 						       skb_len_func,
197 						       skb_time_func,
198 						       backlog, now)) {
199 					/* leave dropping state */
200 					vars->dropping = false;
201 				} else {
202 					/* and schedule the next drop */
203 					vars->drop_next =
204 						codel_control_law(vars->drop_next,
205 								  params->interval,
206 								  vars->rec_inv_sqrt);
207 				}
208 			}
209 		}
210 	} else if (drop) {
211 		u32 delta;
212 
213 		if (params->ecn && INET_ECN_set_ce(skb)) {
214 			stats->ecn_mark++;
215 		} else {
216 			stats->drop_len += skb_len_func(skb);
217 			drop_func(skb, ctx);
218 			stats->drop_count++;
219 
220 			skb = dequeue_func(vars, ctx);
221 			drop = codel_should_drop(skb, ctx, vars, params,
222 						 stats, skb_len_func,
223 						 skb_time_func, backlog, now);
224 		}
225 		vars->dropping = true;
226 		/* if min went above target close to when we last went below it
227 		 * assume that the drop rate that controlled the queue on the
228 		 * last cycle is a good starting point to control it now.
229 		 */
230 		delta = vars->count - vars->lastcount;
231 		if (delta > 1 &&
232 		    codel_time_before(now - vars->drop_next,
233 				      16 * params->interval)) {
234 			vars->count = delta;
235 			/* we dont care if rec_inv_sqrt approximation
236 			 * is not very precise :
237 			 * Next Newton steps will correct it quadratically.
238 			 */
239 			codel_Newton_step(vars);
240 		} else {
241 			vars->count = 1;
242 			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
243 		}
244 		vars->lastcount = vars->count;
245 		vars->drop_next = codel_control_law(now, params->interval,
246 						    vars->rec_inv_sqrt);
247 	}
248 end:
249 	if (skb && codel_time_after(vars->ldelay, params->ce_threshold) &&
250 	    INET_ECN_set_ce(skb))
251 		stats->ce_mark++;
252 	return skb;
253 }
254 
255 #endif
256