LXR linux/include/net/codel

   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
  52static 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
  60static void codel_vars_init(struct codel_vars *vars)
  61{
  62        memset(vars, 0, sizeof(*vars));
  63}
  64
  65static 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 */
  76static 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 */
  93static 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
 100static 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
 142static 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        }
 248end:
 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