codel_impl.h

  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->first_above_time = 0;
162		vars->dropping = false;
163		return skb;
164	}
165	now = codel_get_time();
166	drop = codel_should_drop(skb, ctx, vars, params, stats,
167				 skb_len_func, skb_time_func, backlog, now);
168	if (vars->dropping) {
169		if (!drop) {
170			/* sojourn time below target - leave dropping state */
171			vars->dropping = false;
172		} else if (codel_time_after_eq(now, vars->drop_next)) {
173			/* It's time for the next drop. Drop the current
174			 * packet and dequeue the next. The dequeue might
175			 * take us out of dropping state.
176			 * If not, schedule the next drop.
177			 * A large backlog might result in drop rates so high
178			 * that the next drop should happen now,
179			 * hence the while loop.
180			 */
181			while (vars->dropping &&
182			       codel_time_after_eq(now, vars->drop_next)) {
183				vars->count++; /* dont care of possible wrap
184						* since there is no more divide
185						*/
186				codel_Newton_step(vars);
187				if (params->ecn && INET_ECN_set_ce(skb)) {
188					stats->ecn_mark++;
189					vars->drop_next =
190						codel_control_law(vars->drop_next,
191								  params->interval,
192								  vars->rec_inv_sqrt);
193					goto end;
194				}
195				stats->drop_len += skb_len_func(skb);
196				drop_func(skb, ctx);
197				stats->drop_count++;
198				skb = dequeue_func(vars, ctx);
199				if (!codel_should_drop(skb, ctx,
200						       vars, params, stats,
201						       skb_len_func,
202						       skb_time_func,
203						       backlog, now)) {
204					/* leave dropping state */
205					vars->dropping = false;
206				} else {
207					/* and schedule the next drop */
208					vars->drop_next =
209						codel_control_law(vars->drop_next,
210								  params->interval,
211								  vars->rec_inv_sqrt);
212				}
213			}
214		}
215	} else if (drop) {
216		u32 delta;
217
218		if (params->ecn && INET_ECN_set_ce(skb)) {
219			stats->ecn_mark++;
220		} else {
221			stats->drop_len += skb_len_func(skb);
222			drop_func(skb, ctx);
223			stats->drop_count++;
224
225			skb = dequeue_func(vars, ctx);
226			drop = codel_should_drop(skb, ctx, vars, params,
227						 stats, skb_len_func,
228						 skb_time_func, backlog, now);
229		}
230		vars->dropping = true;
231		/* if min went above target close to when we last went below it
232		 * assume that the drop rate that controlled the queue on the
233		 * last cycle is a good starting point to control it now.
234		 */
235		delta = vars->count - vars->lastcount;
236		if (delta > 1 &&
237		    codel_time_before(now - vars->drop_next,
238				      16 * params->interval)) {
239			vars->count = delta;
240			/* we dont care if rec_inv_sqrt approximation
241			 * is not very precise :
242			 * Next Newton steps will correct it quadratically.
243			 */
244			codel_Newton_step(vars);
245		} else {
246			vars->count = 1;
247			vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
248		}
249		vars->lastcount = vars->count;
250		vars->drop_next = codel_control_law(now, params->interval,
251						    vars->rec_inv_sqrt);
252	}
253end:
254	if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
255		bool set_ce = true;
256
257		if (params->ce_threshold_mask) {
258			int dsfield = skb_get_dsfield(skb);
259
260			set_ce = (dsfield >= 0 &&
261				  (((u8)dsfield & params->ce_threshold_mask) ==
262				   params->ce_threshold_selector));
263		}
264		if (set_ce && INET_ECN_set_ce(skb))
265			stats->ce_mark++;
266	}
267	return skb;
268}
269
270#endif