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  
codel_params_init(struct codel_params * params)54  static 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  
codel_vars_init(struct codel_vars * vars)64  static void codel_vars_init(struct codel_vars *vars)
65  {
66  	memset(vars, 0, sizeof(*vars));
67  }
68  
codel_stats_init(struct codel_stats * stats)69  static 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   */
codel_Newton_step(struct codel_vars * vars)80  static 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   */
codel_control_law(codel_time_t t,codel_time_t interval,u32 rec_inv_sqrt)97  static 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  
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)104  static 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  
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)146  static 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  	}
252  end:
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