include/net/codel_impl.h

   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