bsd/net/classq/classq_red.c

   1 /*
   2  * Copyright (c) 2007-2012 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 /*      $OpenBSD: altq_red.c,v 1.14 2007/09/13 20:40:02 chl Exp $       */
  30 /*      $KAME: altq_red.c,v 1.10 2002/04/03 05:38:51 kjc Exp $  */
  31
  32 /*
  33  * Copyright (C) 1997-2003
  34  *      Sony Computer Science Laboratories Inc.  All rights reserved.
  35  *
  36  * Redistribution and use in source and binary forms, with or without
  37  * modification, are permitted provided that the following conditions
  38  * are met:
  39  * 1. Redistributions of source code must retain the above copyright
  40  *    notice, this list of conditions and the following disclaimer.
  41  * 2. Redistributions in binary form must reproduce the above copyright
  42  *    notice, this list of conditions and the following disclaimer in the
  43  *    documentation and/or other materials provided with the distribution.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY SONY CSL AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL SONY CSL OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  *
  57  */
  58 /*
  59  * Copyright (c) 1990-1994 Regents of the University of California.
  60  * All rights reserved.
  61  *
  62  * Redistribution and use in source and binary forms, with or without
  63  * modification, are permitted provided that the following conditions
  64  * are met:
  65  * 1. Redistributions of source code must retain the above copyright
  66  *    notice, this list of conditions and the following disclaimer.
  67  * 2. Redistributions in binary form must reproduce the above copyright
  68  *    notice, this list of conditions and the following disclaimer in the
  69  *    documentation and/or other materials provided with the distribution.
  70  * 3. All advertising materials mentioning features or use of this software
  71  *    must display the following acknowledgement:
  72  *      This product includes software developed by the Computer Systems
  73  *      Engineering Group at Lawrence Berkeley Laboratory.
  74  * 4. Neither the name of the University nor of the Laboratory may be used
  75  *    to endorse or promote products derived from this software without
  76  *    specific prior written permission.
  77  *
  78  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  79  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  80  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  81  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  82  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  83  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  84  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  85  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  86  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  87  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  88  * SUCH DAMAGE.
  89  */
  90
  91 #include <sys/cdefs.h>
  92
  93 #if CLASSQ_RED
  94
  95 #include <sys/param.h>
  96 #include <sys/malloc.h>
  97 #include <sys/mbuf.h>
  98 #include <sys/socket.h>
  99 #include <sys/systm.h>
 100 #include <sys/syslog.h>
 101 #include <sys/errno.h>
 102 #include <sys/kauth.h>
 103 #include <dev/random/randomdev.h>
 104 #include <kern/zalloc.h>
 105
 106 #include <net/if.h>
 107
 108 #include <netinet/in.h>
 109 #include <netinet/in_systm.h>
 110 #include <netinet/ip.h>
 111 #if INET6
 112 #include <netinet/ip6.h>
 113 #endif
 114
 115 #include <net/classq/classq_red.h>
 116 #include <net/net_osdep.h>
 117
 118 /*
 119  * ALTQ/RED (Random Early Detection) implementation using 32-bit
 120  * fixed-point calculation.
 121  *
 122  * written by kjc using the ns code as a reference.
 123  * you can learn more about red and ns from Sally's home page at
 124  * http://www-nrg.ee.lbl.gov/floyd/
 125  *
 126  * most of the red parameter values are fixed in this implementation
 127  * to prevent fixed-point overflow/underflow.
 128  * if you change the parameters, watch out for overflow/underflow!
 129  *
 130  * the parameters used are recommended values by Sally.
 131  * the corresponding ns config looks:
 132  *      q_weight=0.00195
 133  *      minthresh=5 maxthresh=15 queue-size=60
 134  *      linterm=30
 135  *      dropmech=drop-tail
 136  *      bytes=false (can't be handled by 32-bit fixed-point)
 137  *      doubleq=false dqthresh=false
 138  *      wait=true
 139  */
 140 /*
 141  * alternative red parameters for a slow link.
 142  *
 143  * assume the queue length becomes from zero to L and keeps L, it takes
 144  * N packets for q_avg to reach 63% of L.
 145  * when q_weight is 0.002, N is about 500 packets.
 146  * for a slow link like dial-up, 500 packets takes more than 1 minute!
 147  * when q_weight is 0.008, N is about 127 packets.
 148  * when q_weight is 0.016, N is about 63 packets.
 149  * bursts of 50 packets are allowed for 0.002, bursts of 25 packets
 150  * are allowed for 0.016.
 151  * see Sally's paper for more details.
 152  */
 153 /* normal red parameters */
 154 #define W_WEIGHT        512     /* inverse of weight of EWMA (511/512) */
 155                                 /* q_weight = 0.00195 */
 156
 157 /* red parameters for a slow link */
 158 #define W_WEIGHT_1      128     /* inverse of weight of EWMA (127/128) */
 159                                 /* q_weight = 0.0078125 */
 160
 161 /* red parameters for a very slow link (e.g., dialup) */
 162 #define W_WEIGHT_2      64      /* inverse of weight of EWMA (63/64) */
 163                                 /* q_weight = 0.015625 */
 164
 165 /* fixed-point uses 12-bit decimal places */
 166 #define FP_SHIFT        12      /* fixed-point shift */
 167
 168 /* red parameters for drop probability */
 169 #define INV_P_MAX       10      /* inverse of max drop probability */
 170 #define TH_MIN          5       /* min threshold */
 171 #define TH_MAX          15      /* max threshold */
 172
 173 #define RED_LIMIT       60      /* default max queue lenght */
 174
 175 #define RED_ZONE_MAX    32              /* maximum elements in zone */
 176 #define RED_ZONE_NAME   "classq_red"    /* zone name */
 177
 178 static unsigned int red_size;           /* size of zone element */
 179 static struct zone *red_zone;           /* zone for red */
 180
 181 /*
 182  * our default policy for forced-drop is drop-tail.
 183  * (in altq-1.1.2 or earlier, the default was random-drop.
 184  * but it makes more sense to punish the cause of the surge.)
 185  * to switch to the random-drop policy, define "RED_RANDOM_DROP".
 186  */
 187
 188 /* default red parameter values */
 189 static int default_th_min = TH_MIN;
 190 static int default_th_max = TH_MAX;
 191 static int default_inv_pmax = INV_P_MAX;
 192
 193 static struct mbuf *red_getq_flow(struct red *, class_queue_t *,
 194     u_int32_t, boolean_t);
 195
 196 void
 197 red_init(void)
 198 {
 199         _CASSERT(REDF_ECN4 == CLASSQF_ECN4);
 200         _CASSERT(REDF_ECN6 == CLASSQF_ECN6);
 201
 202         red_size = sizeof (red_t);
 203         red_zone = zinit(red_size, RED_ZONE_MAX * red_size,
 204             0, RED_ZONE_NAME);
 205         if (red_zone == NULL) {
 206                 panic("%s: failed allocating %s", __func__, RED_ZONE_NAME);
 207                 /* NOTREACHED */
 208         }
 209         zone_change(red_zone, Z_EXPAND, TRUE);
 210         zone_change(red_zone, Z_CALLERACCT, TRUE);
 211 }
 212
 213 /*
 214  * red support routines
 215  */
 216 red_t *
 217 red_alloc(struct ifnet *ifp, int weight, int inv_pmax, int th_min,
 218     int th_max, int flags, int pkttime)
 219 {
 220         red_t   *rp;
 221         int      w, i;
 222         int      npkts_per_sec;
 223
 224         VERIFY(ifp != NULL);
 225
 226         rp = zalloc(red_zone);
 227         if (rp == NULL)
 228                 return (NULL);
 229
 230         bzero(rp, red_size);
 231         rp->red_avg = 0;
 232         rp->red_idle = 1;
 233
 234         if (weight == 0)
 235                 rp->red_weight = W_WEIGHT;
 236         else
 237                 rp->red_weight = weight;
 238         if (inv_pmax == 0)
 239                 rp->red_inv_pmax = default_inv_pmax;
 240         else
 241                 rp->red_inv_pmax = inv_pmax;
 242         if (th_min == 0)
 243                 rp->red_thmin = default_th_min;
 244         else
 245                 rp->red_thmin = th_min;
 246         if (th_max == 0)
 247                 rp->red_thmax = default_th_max;
 248         else
 249                 rp->red_thmax = th_max;
 250
 251         rp->red_ifp = ifp;
 252         rp->red_flags = (flags & REDF_USERFLAGS);
 253 #if !PF_ECN
 254         if (rp->red_flags & REDF_ECN) {
 255                 rp->red_flags &= ~REDF_ECN;
 256                 log(LOG_ERR, "%s: RED ECN not available; ignoring "
 257                     "REDF_ECN flag!\n", if_name(ifp));
 258         }
 259 #endif /* !PF_ECN */
 260
 261         if (pkttime == 0)
 262                 /* default packet time: 1000 bytes / 10Mbps * 8 * 1000000 */
 263                 rp->red_pkttime = 800;
 264         else
 265                 rp->red_pkttime = pkttime;
 266
 267         if (weight == 0) {
 268                 /* when the link is very slow, adjust red parameters */
 269                 npkts_per_sec = 1000000 / rp->red_pkttime;
 270                 if (npkts_per_sec < 50) {
 271                         /* up to about 400Kbps */
 272                         rp->red_weight = W_WEIGHT_2;
 273                 } else if (npkts_per_sec < 300) {
 274                         /* up to about 2.4Mbps */
 275                         rp->red_weight = W_WEIGHT_1;
 276                 }
 277         }
 278
 279         /* calculate wshift.  weight must be power of 2 */
 280         w = rp->red_weight;
 281         for (i = 0; w > 1; i++)
 282                 w = w >> 1;
 283         rp->red_wshift = i;
 284         w = 1 << rp->red_wshift;
 285         if (w != rp->red_weight) {
 286                 printf("invalid weight value %d for red! use %d\n",
 287                     rp->red_weight, w);
 288                 rp->red_weight = w;
 289         }
 290
 291         /*
 292          * thmin_s and thmax_s are scaled versions of th_min and th_max
 293          * to be compared with avg.
 294          */
 295         rp->red_thmin_s = rp->red_thmin << (rp->red_wshift + FP_SHIFT);
 296         rp->red_thmax_s = rp->red_thmax << (rp->red_wshift + FP_SHIFT);
 297
 298         /*
 299          * precompute probability denominator
 300          *  probd = (2 * (TH_MAX-TH_MIN) / pmax) in fixed-point
 301          */
 302         rp->red_probd = (2 * (rp->red_thmax - rp->red_thmin) *
 303             rp->red_inv_pmax) << FP_SHIFT;
 304
 305         /* allocate weight table */
 306         rp->red_wtab = wtab_alloc(rp->red_weight);
 307         if (rp->red_wtab == NULL) {
 308                 red_destroy(rp);
 309                 return (NULL);
 310         }
 311
 312         microuptime(&rp->red_last);
 313         return (rp);
 314 }
 315
 316 void
 317 red_destroy(red_t *rp)
 318 {
 319         if (rp->red_wtab != NULL) {
 320                 wtab_destroy(rp->red_wtab);
 321                 rp->red_wtab = NULL;
 322         }
 323         zfree(red_zone, rp);
 324 }
 325
 326 void
 327 red_getstats(red_t *rp, struct red_stats *sp)
 328 {
 329         sp->q_avg               = rp->red_avg >> rp->red_wshift;
 330         sp->drop_forced         = rp->red_stats.drop_forced;
 331         sp->drop_unforced       = rp->red_stats.drop_unforced;
 332         sp->marked_packets      = rp->red_stats.marked_packets;
 333 }
 334
 335 int
 336 red_addq(red_t *rp, class_queue_t *q, struct mbuf *m, struct pf_mtag *tag)
 337 {
 338 #if !PF_ECN
 339 #pragma unused(tag)
 340 #endif /* !PF_ECN */
 341         int avg, droptype;
 342         int n;
 343
 344         avg = rp->red_avg;
 345
 346         /*
 347          * if we were idle, we pretend that n packets arrived during
 348          * the idle period.
 349          */
 350         if (rp->red_idle) {
 351                 struct timeval now;
 352                 int t;
 353
 354                 rp->red_idle = 0;
 355                 microuptime(&now);
 356                 t = (now.tv_sec - rp->red_last.tv_sec);
 357                 if (t > 60) {
 358                         /*
 359                          * being idle for more than 1 minute, set avg to zero.
 360                          * this prevents t from overflow.
 361                          */
 362                         avg = 0;
 363                 } else {
 364                         t = t * 1000000 + (now.tv_usec - rp->red_last.tv_usec);
 365                         n = t / rp->red_pkttime - 1;
 366
 367                         /* the following line does (avg = (1 - Wq)^n * avg) */
 368                         if (n > 0)
 369                                 avg = (avg >> FP_SHIFT) *
 370                                     pow_w(rp->red_wtab, n);
 371                 }
 372         }
 373
 374         /* run estimator. (note: avg is scaled by WEIGHT in fixed-point) */
 375         avg += (qlen(q) << FP_SHIFT) - (avg >> rp->red_wshift);
 376         rp->red_avg = avg;              /* save the new value */
 377
 378         /*
 379          * red_count keeps a tally of arriving traffic that has not
 380          * been dropped.
 381          */
 382         rp->red_count++;
 383
 384         /* see if we drop early */
 385         droptype = DTYPE_NODROP;
 386         if (avg >= rp->red_thmin_s && qlen(q) > 1) {
 387                 if (avg >= rp->red_thmax_s) {
 388                         /* avg >= th_max: forced drop */
 389                         droptype = DTYPE_FORCED;
 390                 } else if (rp->red_old == 0) {
 391                         /* first exceeds th_min */
 392                         rp->red_count = 1;
 393                         rp->red_old = 1;
 394                 } else if (drop_early((avg - rp->red_thmin_s) >> rp->red_wshift,
 395                     rp->red_probd, rp->red_count)) {
 396                         /* mark or drop by red */
 397 #if PF_ECN
 398                         if ((rp->red_flags & REDF_ECN) &&
 399                             (tag->pftag_proto == IPPROTO_TCP) && /* only TCP */
 400                             mark_ecn(m, tag, rp->red_flags)) {
 401                                 /* successfully marked.  do not drop. */
 402                                 rp->red_count = 0;
 403                                 rp->red_stats.marked_packets++;
 404                         } else
 405 #endif /* PF_ECN */
 406                         {
 407                                 /* unforced drop by red */
 408                                 droptype = DTYPE_EARLY;
 409                         }
 410                 }
 411         } else {
 412                 /* avg < th_min */
 413                 rp->red_old = 0;
 414         }
 415
 416         /*
 417          * if the queue length hits the hard limit, it's a forced drop.
 418          */
 419         if (droptype == DTYPE_NODROP && qlen(q) >= qlimit(q))
 420                 droptype = DTYPE_FORCED;
 421
 422 #ifdef RED_RANDOM_DROP
 423         /* if successful or forced drop, enqueue this packet. */
 424         if (droptype != DTYPE_EARLY)
 425                 _addq(q, m);
 426 #else
 427         /* if successful, enqueue this packet. */
 428         if (droptype == DTYPE_NODROP)
 429                 _addq(q, m);
 430 #endif
 431         if (droptype != DTYPE_NODROP) {
 432                 if (droptype == DTYPE_EARLY) {
 433                         /* drop the incoming packet */
 434                         rp->red_stats.drop_unforced++;
 435                 } else {
 436                         /* forced drop, select a victim packet in the queue. */
 437 #ifdef RED_RANDOM_DROP
 438                         m = _getq_random(q);
 439 #endif
 440                         rp->red_stats.drop_forced++;
 441                 }
 442                 rp->red_count = 0;
 443                 IFCQ_CONVERT_LOCK(&rp->red_ifp->if_snd);
 444                 m_freem(m);
 445                 return (CLASSQEQ_DROPPED);
 446         }
 447         /* successfully queued */
 448         return (CLASSQEQ_SUCCESS);
 449 }
 450
 451 /*
 452  * early-drop probability is calculated as follows:
 453  *   prob = p_max * (avg - th_min) / (th_max - th_min)
 454  *   prob_a = prob / (2 - count*prob)
 455  *          = (avg-th_min) / (2*(th_max-th_min)*inv_p_max - count*(avg-th_min))
 456  * here prob_a increases as successive undrop count increases.
 457  * (prob_a starts from prob/2, becomes prob when (count == (1 / prob)),
 458  * becomes 1 when (count >= (2 / prob))).
 459  */
 460 int
 461 drop_early(int fp_len, int fp_probd, int count)
 462 {
 463         int     d;              /* denominator of drop-probability */
 464
 465         d = fp_probd - count * fp_len;
 466         if (d <= 0)
 467                 /* count exceeds the hard limit: drop or mark */
 468                 return (1);
 469
 470         /*
 471          * now the range of d is [1..600] in fixed-point. (when
 472          * th_max-th_min=10 and p_max=1/30)
 473          * drop probability = (avg - TH_MIN) / d
 474          */
 475
 476         if ((RandomULong() % d) < (unsigned)fp_len) {
 477                 /* drop or mark */
 478                 return (1);
 479         }
 480         /* no drop/mark */
 481         return (0);
 482 }
 483
 484 static struct mbuf *
 485 red_getq_flow(struct red *rp, class_queue_t *q, u_int32_t flow, boolean_t purge)
 486 {
 487 #pragma unused(purge)
 488         struct mbuf *m;
 489
 490         /* flow of 0 means head of queue */
 491         if ((m = ((flow == 0) ? _getq(q) : _getq_flow(q, flow))) == NULL) {
 492                 if (rp->red_idle == 0) {
 493                         rp->red_idle = 1;
 494                         microuptime(&rp->red_last);
 495                 }
 496                 return (NULL);
 497         }
 498
 499         rp->red_idle = 0;
 500         return (m);
 501 }
 502
 503 struct mbuf *
 504 red_getq(red_t *rp, class_queue_t *q)
 505 {
 506         return (red_getq_flow(rp, q, 0, FALSE));
 507 }
 508
 509 void
 510 red_purgeq(struct red *rp, class_queue_t *q, u_int32_t flow, u_int32_t *packets,
 511     u_int32_t *bytes)
 512 {
 513         u_int32_t cnt = 0, len = 0;
 514         struct mbuf *m;
 515
 516         IFCQ_CONVERT_LOCK(&rp->red_ifp->if_snd);
 517
 518         while ((m = red_getq_flow(rp, q, flow, TRUE)) != NULL) {
 519                 cnt++;
 520                 len += m_pktlen(m);
 521                 m_freem(m);
 522         }
 523
 524         if (packets != NULL)
 525                 *packets = cnt;
 526         if (bytes != NULL)
 527                 *bytes = len;
 528 }
 529
 530 void
 531 red_updateq(red_t *rp, cqev_t ev)
 532 {
 533 #pragma unused(rp, ev)
 534         /* nothing for now */
 535 }
 536
 537 int
 538 red_suspendq(red_t *rp, class_queue_t *q, boolean_t on)
 539 {
 540 #pragma unused(rp, q, on)
 541         return (ENOTSUP);
 542 }
 543
 544 /*
 545  * helper routine to calibrate avg during idle.
 546  * pow_w(wtab, n) returns (1 - Wq)^n in fixed-point
 547  * here Wq = 1/weight and the code assumes Wq is close to zero.
 548  *
 549  * w_tab[n] holds ((1 - Wq)^(2^n)) in fixed-point.
 550  */
 551 static struct wtab *wtab_list = NULL;   /* pointer to wtab list */
 552
 553 struct wtab *
 554 wtab_alloc(int weight)
 555 {
 556         struct wtab     *w;
 557         int              i;
 558
 559         for (w = wtab_list; w != NULL; w = w->w_next)
 560                 if (w->w_weight == weight) {
 561                         w->w_refcount++;
 562                         return (w);
 563                 }
 564
 565         w = _MALLOC(sizeof (struct wtab), M_DEVBUF, M_WAITOK|M_ZERO);
 566         if (w == NULL)
 567                 return (NULL);
 568
 569         w->w_weight = weight;
 570         w->w_refcount = 1;
 571         w->w_next = wtab_list;
 572         wtab_list = w;
 573
 574         /* initialize the weight table */
 575         w->w_tab[0] = ((weight - 1) << FP_SHIFT) / weight;
 576         for (i = 1; i < 32; i++) {
 577                 w->w_tab[i] = (w->w_tab[i-1] * w->w_tab[i-1]) >> FP_SHIFT;
 578                 if (w->w_tab[i] == 0 && w->w_param_max == 0)
 579                         w->w_param_max = 1 << i;
 580         }
 581
 582         return (w);
 583 }
 584
 585 void
 586 wtab_destroy(struct wtab *w)
 587 {
 588         struct wtab     *prev;
 589
 590         if (--w->w_refcount > 0)
 591                 return;
 592
 593         if (wtab_list == w)
 594                 wtab_list = w->w_next;
 595         else for (prev = wtab_list; prev->w_next != NULL; prev = prev->w_next)
 596                 if (prev->w_next == w) {
 597                         prev->w_next = w->w_next;
 598                         break;
 599                 }
 600
 601         _FREE(w, M_DEVBUF);
 602 }
 603
 604 int32_t
 605 pow_w(struct wtab *w, int n)
 606 {
 607         int     i, bit;
 608         int32_t val;
 609
 610         if (n >= w->w_param_max)
 611                 return (0);
 612
 613         val = 1 << FP_SHIFT;
 614         if (n <= 0)
 615                 return (val);
 616
 617         bit = 1;
 618         i = 0;
 619         while (n) {
 620                 if (n & bit) {
 621                         val = (val * w->w_tab[i]) >> FP_SHIFT;
 622                         n &= ~bit;
 623                 }
 624                 i++;
 625                 bit <<=  1;
 626         }
 627         return (val);
 628 }
 629
 630 #endif /* CLASSQ_RED */