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->ce_threshold_mask = 0; 58 params->ce_threshold_selector = 0; 59 params->ecn = false; 60 } 61 62 static void codel_vars_init(struct codel_vars *vars) 63 { 64 memset(vars, 0, sizeof(*vars)); 65 } 66 67 static void codel_stats_init(struct codel_stats *stats) 68 { 69 stats->maxpacket = 0; 70 } 71 72 /* 73 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots 74 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2) 75 * 76 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32 77 */ 78 static void codel_Newton_step(struct codel_vars *vars) 79 { 80 u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT; 81 u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32; 82 u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2); 83 84 val >>= 2; /* avoid overflow in following multiply */ 85 val = (val * invsqrt) >> (32 - 2 + 1); 86 87 vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT; 88 } 89 90 /* 91 * CoDel control_law is t + interval/sqrt(count) 92 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid 93 * both sqrt() and divide operation. 94 */ 95 static codel_time_t codel_control_law(codel_time_t t, 96 codel_time_t interval, 97 u32 rec_inv_sqrt) 98 { 99 return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT); 100 } 101 102 static bool codel_should_drop(const struct sk_buff *skb, 103 void *ctx, 104 struct codel_vars *vars, 105 struct codel_params *params, 106 struct codel_stats *stats, 107 codel_skb_len_t skb_len_func, 108 codel_skb_time_t skb_time_func, 109 u32 *backlog, 110 codel_time_t now) 111 { 112 bool ok_to_drop; 113 u32 skb_len; 114 115 if (!skb) { 116 vars->first_above_time = 0; 117 return false; 118 } 119 120 skb_len = skb_len_func(skb); 121 vars->ldelay = now - skb_time_func(skb); 122 123 if (unlikely(skb_len > stats->maxpacket)) 124 stats->maxpacket = skb_len; 125 126 if (codel_time_before(vars->ldelay, params->target) || 127 *backlog <= params->mtu) { 128 /* went below - stay below for at least interval */ 129 vars->first_above_time = 0; 130 return false; 131 } 132 ok_to_drop = false; 133 if (vars->first_above_time == 0) { 134 /* just went above from below. If we stay above 135 * for at least interval we'll say it's ok to drop 136 */ 137 vars->first_above_time = now + params->interval; 138 } else if (codel_time_after(now, vars->first_above_time)) { 139 ok_to_drop = true; 140 } 141 return ok_to_drop; 142 } 143 144 static struct sk_buff *codel_dequeue(void *ctx, 145 u32 *backlog, 146 struct codel_params *params, 147 struct codel_vars *vars, 148 struct codel_stats *stats, 149 codel_skb_len_t skb_len_func, 150 codel_skb_time_t skb_time_func, 151 codel_skb_drop_t drop_func, 152 codel_skb_dequeue_t dequeue_func) 153 { 154 struct sk_buff *skb = dequeue_func(vars, ctx); 155 codel_time_t now; 156 bool drop; 157 158 if (!skb) { 159 vars->dropping = false; 160 return skb; 161 } 162 now = codel_get_time(); 163 drop = codel_should_drop(skb, ctx, vars, params, stats, 164 skb_len_func, skb_time_func, backlog, now); 165 if (vars->dropping) { 166 if (!drop) { 167 /* sojourn time below target - leave dropping state */ 168 vars->dropping = false; 169 } else if (codel_time_after_eq(now, vars->drop_next)) { 170 /* It's time for the next drop. Drop the current 171 * packet and dequeue the next. The dequeue might 172 * take us out of dropping state. 173 * If not, schedule the next drop. 174 * A large backlog might result in drop rates so high 175 * that the next drop should happen now, 176 * hence the while loop. 177 */ 178 while (vars->dropping && 179 codel_time_after_eq(now, vars->drop_next)) { 180 vars->count++; /* dont care of possible wrap 181 * since there is no more divide 182 */ 183 codel_Newton_step(vars); 184 if (params->ecn && INET_ECN_set_ce(skb)) { 185 stats->ecn_mark++; 186 vars->drop_next = 187 codel_control_law(vars->drop_next, 188 params->interval, 189 vars->rec_inv_sqrt); 190 goto end; 191 } 192 stats->drop_len += skb_len_func(skb); 193 drop_func(skb, ctx); 194 stats->drop_count++; 195 skb = dequeue_func(vars, ctx); 196 if (!codel_should_drop(skb, ctx, 197 vars, params, stats, 198 skb_len_func, 199 skb_time_func, 200 backlog, now)) { 201 /* leave dropping state */ 202 vars->dropping = false; 203 } else { 204 /* and schedule the next drop */ 205 vars->drop_next = 206 codel_control_law(vars->drop_next, 207 params->interval, 208 vars->rec_inv_sqrt); 209 } 210 } 211 } 212 } else if (drop) { 213 u32 delta; 214 215 if (params->ecn && INET_ECN_set_ce(skb)) { 216 stats->ecn_mark++; 217 } else { 218 stats->drop_len += skb_len_func(skb); 219 drop_func(skb, ctx); 220 stats->drop_count++; 221 222 skb = dequeue_func(vars, ctx); 223 drop = codel_should_drop(skb, ctx, vars, params, 224 stats, skb_len_func, 225 skb_time_func, backlog, now); 226 } 227 vars->dropping = true; 228 /* if min went above target close to when we last went below it 229 * assume that the drop rate that controlled the queue on the 230 * last cycle is a good starting point to control it now. 231 */ 232 delta = vars->count - vars->lastcount; 233 if (delta > 1 && 234 codel_time_before(now - vars->drop_next, 235 16 * params->interval)) { 236 vars->count = delta; 237 /* we dont care if rec_inv_sqrt approximation 238 * is not very precise : 239 * Next Newton steps will correct it quadratically. 240 */ 241 codel_Newton_step(vars); 242 } else { 243 vars->count = 1; 244 vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT; 245 } 246 vars->lastcount = vars->count; 247 vars->drop_next = codel_control_law(now, params->interval, 248 vars->rec_inv_sqrt); 249 } 250 end: 251 if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) { 252 bool set_ce = true; 253 254 if (params->ce_threshold_mask) { 255 int dsfield = skb_get_dsfield(skb); 256 257 set_ce = (dsfield >= 0 && 258 (((u8)dsfield & params->ce_threshold_mask) == 259 params->ce_threshold_selector)); 260 } 261 if (set_ce && INET_ECN_set_ce(skb)) 262 stats->ce_mark++; 263 } 264 return skb; 265 } 266 267 #endif 268