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 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 64 static void codel_vars_init(struct codel_vars *vars) 65 { 66 memset(vars, 0, sizeof(*vars)); 67 } 68 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 */ 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 */ 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 } 103 104 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 } 145 146 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