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| 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 |
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