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 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 60 static void codel_vars_init(struct codel_vars *vars) 61 { 62 memset(vars, 0, sizeof(*vars)); 63 } 64 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 */ 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 */ 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 } 99 100 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 } 141 142 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