FreeBSD/Linux Kernel Cross Reference
sys/netinet/cc/cc_cdg.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2009-2013
      *      Swinburne University of Technology, Melbourne, Australia
      * All rights reserved.
      *
      * This software was developed at the Centre for Advanced Internet
      * Architectures, Swinburne University of Technology, by David Hayes, made
     * possible in part by a gift from The Cisco University Research Program Fund,
     * a corporate advised fund of Silicon Valley Community Foundation. Development
     * and testing were further assisted by a grant from the FreeBSD Foundation.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*
     * CAIA Delay-Gradient (CDG) congestion control algorithm
     *
     * An implemention of the delay-gradient congestion control algorithm proposed
     * in the following paper:
     *
     * D. A. Hayes and G. Armitage, "Revisiting TCP Congestion Control using Delay
     * Gradients", in IFIP Networking, Valencia, Spain, 9-13 May 2011.
     *
     * Developed as part of the NewTCP research project at Swinburne University of
     * Technology's Centre for Advanced Internet Architectures, Melbourne,
     * Australia. More details are available at:
     *   http://caia.swin.edu.au/urp/newtcp/
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/hhook.h>
    #include <sys/kernel.h>
    #include <sys/khelp.h>
    #include <sys/limits.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/module.h>
    #include <sys/queue.h>
    #include <sys/socket.h>
    #include <sys/socketvar.h>
    #include <sys/sysctl.h>
    #include <sys/systm.h>
    
    #include <net/vnet.h>
    
    #include <net/route.h>
    #include <net/route/nhop.h>
    
    #include <netinet/in_pcb.h>
    #include <netinet/tcp.h>
    #include <netinet/tcp_seq.h>
    #include <netinet/tcp_timer.h>
    #include <netinet/tcp_var.h>
    #include <netinet/cc/cc.h>
    #include <netinet/cc/cc_module.h>
    
    #include <netinet/khelp/h_ertt.h>
    
    #include <vm/uma.h>
    
    #define CDG_VERSION "0.1"
    
    /* Private delay-gradient induced congestion control signal. */
    #define CC_CDG_DELAY 0x01000000
    
    /* NewReno window deflation factor on loss (as a percentage). */
    #define RENO_BETA 50
    
    /* Queue states. */
    #define CDG_Q_EMPTY     1
    #define CDG_Q_RISING    2
    #define CDG_Q_FALLING   3
    #define CDG_Q_FULL      4
    #define CDG_Q_UNKNOWN   9999
    
   /* Number of bit shifts used in probexp lookup table. */
   #define EXP_PREC 15
   
   /* Largest gradient represented in probexp lookup table. */
   #define MAXGRAD 5
   
   /*
    * Delay Precision Enhance - number of bit shifts used for qtrend related
    * integer arithmetic precision.
    */
   #define D_P_E 7
   
   struct qdiff_sample {
           long qdiff;
           STAILQ_ENTRY(qdiff_sample) qdiff_lnk;
   };
   
   struct cdg {
           long max_qtrend;
           long min_qtrend;
           STAILQ_HEAD(minrtts_head, qdiff_sample) qdiffmin_q;
           STAILQ_HEAD(maxrtts_head, qdiff_sample) qdiffmax_q;
           long window_incr;
           /* rttcount for window increase when in congestion avoidance */
           long rtt_count;
           /* maximum measured rtt within an rtt period */
           int maxrtt_in_rtt;
           /* maximum measured rtt within prev rtt period */
           int maxrtt_in_prevrtt;
           /* minimum measured rtt within an rtt period */
           int minrtt_in_rtt;
           /* minimum measured rtt within prev rtt period */
           int minrtt_in_prevrtt;
           /* consecutive congestion episode counter */
           uint32_t consec_cong_cnt;
           /* when tracking a new reno type loss window */
           uint32_t shadow_w;
           /* maximum number of samples in the moving average queue */
           int sample_q_size;
           /* number of samples in the moving average queue */
           int num_samples;
           /* estimate of the queue state of the path */
           int queue_state;
   };
   
   /*
    * Lookup table for:
    *   (1 - exp(-x)) << EXP_PREC, where x = [0,MAXGRAD] in 2^-7 increments
    *
    * Note: probexp[0] is set to 10 (not 0) as a safety for very low increase
    * gradients.
    */
   static const int probexp[641] = {
      10,255,508,759,1008,1255,1501,1744,1985,2225,2463,2698,2932,3165,3395,3624,
      3850,4075,4299,4520,4740,4958,5175,5389,5602,5814,6024,6232,6438,6643,6846,
      7048,7248,7447,7644,7839,8033,8226,8417,8606,8794,8981,9166,9350,9532,9713,
      9892,10070,10247,10422,10596,10769,10940,11110,11278,11445,11611,11776,11939,
      12101,12262,12422,12580,12737,12893,13048,13201,13354,13505,13655,13803,13951,
      14097,14243,14387,14530,14672,14813,14952,15091,15229,15365,15500,15635,15768,
      15900,16032,16162,16291,16419,16547,16673,16798,16922,17046,17168,17289,17410,
      17529,17648,17766,17882,17998,18113,18227,18340,18453,18564,18675,18784,18893,
      19001,19108,19215,19320,19425,19529,19632,19734,19835,19936,20036,20135,20233,
      20331,20427,20523,20619,20713,20807,20900,20993,21084,21175,21265,21355,21444,
      21532,21619,21706,21792,21878,21962,22046,22130,22213,22295,22376,22457,22537,
      22617,22696,22774,22852,22929,23006,23082,23157,23232,23306,23380,23453,23525,
      23597,23669,23739,23810,23879,23949,24017,24085,24153,24220,24286,24352,24418,
      24483,24547,24611,24675,24738,24800,24862,24924,24985,25045,25106,25165,25224,
      25283,25341,25399,25456,25513,25570,25626,25681,25737,25791,25846,25899,25953,
      26006,26059,26111,26163,26214,26265,26316,26366,26416,26465,26514,26563,26611,
      26659,26707,26754,26801,26847,26893,26939,26984,27029,27074,27118,27162,27206,
      27249,27292,27335,27377,27419,27460,27502,27543,27583,27624,27664,27703,27743,
      27782,27821,27859,27897,27935,27973,28010,28047,28084,28121,28157,28193,28228,
      28263,28299,28333,28368,28402,28436,28470,28503,28536,28569,28602,28634,28667,
      28699,28730,28762,28793,28824,28854,28885,28915,28945,28975,29004,29034,29063,
      29092,29120,29149,29177,29205,29232,29260,29287,29314,29341,29368,29394,29421,
      29447,29472,29498,29524,29549,29574,29599,29623,29648,29672,29696,29720,29744,
      29767,29791,29814,29837,29860,29882,29905,29927,29949,29971,29993,30014,30036,
      30057,30078,30099,30120,30141,30161,30181,30201,30221,30241,30261,30280,30300,
      30319,30338,30357,30376,30394,30413,30431,30449,30467,30485,30503,30521,30538,
      30555,30573,30590,30607,30624,30640,30657,30673,30690,30706,30722,30738,30753,
      30769,30785,30800,30815,30831,30846,30861,30876,30890,30905,30919,30934,30948,
      30962,30976,30990,31004,31018,31031,31045,31058,31072,31085,31098,31111,31124,
      31137,31149,31162,31174,31187,31199,31211,31223,31235,31247,31259,31271,31283,
      31294,31306,31317,31328,31339,31351,31362,31373,31383,31394,31405,31416,31426,
      31436,31447,31457,31467,31477,31487,31497,31507,31517,31527,31537,31546,31556,
      31565,31574,31584,31593,31602,31611,31620,31629,31638,31647,31655,31664,31673,
      31681,31690,31698,31706,31715,31723,31731,31739,31747,31755,31763,31771,31778,
      31786,31794,31801,31809,31816,31824,31831,31838,31846,31853,31860,31867,31874,
      31881,31888,31895,31902,31908,31915,31922,31928,31935,31941,31948,31954,31960,
      31967,31973,31979,31985,31991,31997,32003,32009,32015,32021,32027,32033,32038,
      32044,32050,32055,32061,32066,32072,32077,32083,32088,32093,32098,32104,32109,
      32114,32119,32124,32129,32134,32139,32144,32149,32154,32158,32163,32168,32173,
      32177,32182,32186,32191,32195,32200,32204,32209,32213,32217,32222,32226,32230,
      32234,32238,32242,32247,32251,32255,32259,32263,32267,32270,32274,32278,32282,
      32286,32290,32293,32297,32301,32304,32308,32311,32315,32318,32322,32325,32329,
      32332,32336,32339,32342,32346,32349,32352,32356,32359,32362,32365,32368,32371,
      32374,32377,32381,32384,32387,32389,32392,32395,32398,32401,32404,32407,32410,
      32412,32415,32418,32421,32423,32426,32429,32431,32434,32437,32439,32442,32444,
      32447,32449,32452,32454,32457,32459,32461,32464,32466,32469,32471,32473,32476,
      32478,32480,32482,32485,32487,32489,32491,32493,32495,32497,32500,32502,32504,
      32506,32508,32510,32512,32514,32516,32518,32520,32522,32524,32526,32527,32529,
      32531,32533,32535,32537,32538,32540,32542,32544,32545,32547};
   
   static uma_zone_t qdiffsample_zone;
   static int ertt_id;
   
   VNET_DEFINE_STATIC(uint32_t, cdg_alpha_inc);
   VNET_DEFINE_STATIC(uint32_t, cdg_beta_delay);
   VNET_DEFINE_STATIC(uint32_t, cdg_beta_loss);
   VNET_DEFINE_STATIC(uint32_t, cdg_smoothing_factor);
   VNET_DEFINE_STATIC(uint32_t, cdg_exp_backoff_scale);
   VNET_DEFINE_STATIC(uint32_t, cdg_consec_cong);
   VNET_DEFINE_STATIC(uint32_t, cdg_hold_backoff);
   #define V_cdg_alpha_inc         VNET(cdg_alpha_inc)
   #define V_cdg_beta_delay        VNET(cdg_beta_delay)
   #define V_cdg_beta_loss         VNET(cdg_beta_loss)
   #define V_cdg_smoothing_factor  VNET(cdg_smoothing_factor)
   #define V_cdg_exp_backoff_scale VNET(cdg_exp_backoff_scale)
   #define V_cdg_consec_cong       VNET(cdg_consec_cong)
   #define V_cdg_hold_backoff      VNET(cdg_hold_backoff)
   
   /* Function prototypes. */
   static int cdg_mod_init(void);
   static int cdg_mod_destroy(void);
   static void cdg_conn_init(struct cc_var *ccv);
   static int cdg_cb_init(struct cc_var *ccv, void *ptr);
   static void cdg_cb_destroy(struct cc_var *ccv);
   static void cdg_cong_signal(struct cc_var *ccv, uint32_t signal_type);
   static void cdg_ack_received(struct cc_var *ccv, uint16_t ack_type);
   static size_t cdg_data_sz(void);
   
   struct cc_algo cdg_cc_algo = {
           .name = "cdg",
           .mod_init = cdg_mod_init,
           .ack_received = cdg_ack_received,
           .cb_destroy = cdg_cb_destroy,
           .cb_init = cdg_cb_init,
           .conn_init = cdg_conn_init,
           .cong_signal = cdg_cong_signal,
           .mod_destroy = cdg_mod_destroy,
           .cc_data_sz = cdg_data_sz,
           .post_recovery = newreno_cc_post_recovery,
           .after_idle = newreno_cc_after_idle,
   };
   
   /* Vnet created and being initialised. */
   static void
   cdg_init_vnet(const void *unused __unused)
   {
   
           V_cdg_alpha_inc = 0;
           V_cdg_beta_delay = 70;
           V_cdg_beta_loss = 50;
           V_cdg_smoothing_factor = 8;
           V_cdg_exp_backoff_scale = 3;
           V_cdg_consec_cong = 5;
           V_cdg_hold_backoff = 5;
   }
   
   static int
   cdg_mod_init(void)
   {
           VNET_ITERATOR_DECL(v);
   
           ertt_id = khelp_get_id("ertt");
           if (ertt_id <= 0)
                   return (EINVAL);
   
           qdiffsample_zone = uma_zcreate("cdg_qdiffsample",
               sizeof(struct qdiff_sample), NULL, NULL, NULL, NULL, 0, 0);
   
           VNET_LIST_RLOCK();
           VNET_FOREACH(v) {
                   CURVNET_SET(v);
                   cdg_init_vnet(NULL);
                   CURVNET_RESTORE();
           }
           VNET_LIST_RUNLOCK();
           return (0);
   }
   
   static int
   cdg_mod_destroy(void)
   {
   
           uma_zdestroy(qdiffsample_zone);
           return (0);
   }
   
   static size_t
   cdg_data_sz(void)
   {
           return (sizeof(struct cdg));
   }
   
   static int
   cdg_cb_init(struct cc_var *ccv, void *ptr)
   {
           struct cdg *cdg_data;
   
           INP_WLOCK_ASSERT(tptoinpcb(ccv->ccvc.tcp));
           if (ptr == NULL) {
                   cdg_data = malloc(sizeof(struct cdg), M_CC_MEM, M_NOWAIT);
                   if (cdg_data == NULL)
                           return (ENOMEM);
           } else {
                   cdg_data = ptr;
           }
           cdg_data->shadow_w = 0;
           cdg_data->max_qtrend = 0;
           cdg_data->min_qtrend = 0;
           cdg_data->queue_state = CDG_Q_UNKNOWN;
           cdg_data->maxrtt_in_rtt = 0;
           cdg_data->maxrtt_in_prevrtt = 0;
           cdg_data->minrtt_in_rtt = INT_MAX;
           cdg_data->minrtt_in_prevrtt = 0;
           cdg_data->window_incr = 0;
           cdg_data->rtt_count = 0;
           cdg_data->consec_cong_cnt = 0;
           cdg_data->sample_q_size = V_cdg_smoothing_factor;
           cdg_data->num_samples = 0;
           STAILQ_INIT(&cdg_data->qdiffmin_q);
           STAILQ_INIT(&cdg_data->qdiffmax_q);
   
           ccv->cc_data = cdg_data;
   
           return (0);
   }
   
   static void
   cdg_conn_init(struct cc_var *ccv)
   {
           struct cdg *cdg_data = ccv->cc_data;
   
           /*
            * Initialise the shadow_cwnd in case we are competing with loss based
            * flows from the start
            */
           cdg_data->shadow_w = CCV(ccv, snd_cwnd);
   }
   
   static void
   cdg_cb_destroy(struct cc_var *ccv)
   {
           struct cdg *cdg_data;
           struct qdiff_sample *qds, *qds_n;
   
           cdg_data = ccv->cc_data;
   
           qds = STAILQ_FIRST(&cdg_data->qdiffmin_q);
           while (qds != NULL) {
                   qds_n = STAILQ_NEXT(qds, qdiff_lnk);
                   uma_zfree(qdiffsample_zone,qds);
                   qds = qds_n;
           }
   
           qds = STAILQ_FIRST(&cdg_data->qdiffmax_q);
           while (qds != NULL) {
                   qds_n = STAILQ_NEXT(qds, qdiff_lnk);
                   uma_zfree(qdiffsample_zone,qds);
                   qds = qds_n;
           }
   
           free(ccv->cc_data, M_CC_MEM);
   }
   
   static int
   cdg_beta_handler(SYSCTL_HANDLER_ARGS)
   {
           int error;
           uint32_t new;
   
           new = *(uint32_t *)arg1;
           error = sysctl_handle_int(oidp, &new, 0, req);
           if (error == 0 && req->newptr != NULL) {
                   if (new == 0 || new > 100)
                           error = EINVAL;
                   else
                           *(uint32_t *)arg1 = new;
           }
   
           return (error);
   }
   
   static int
   cdg_exp_backoff_scale_handler(SYSCTL_HANDLER_ARGS)
   {
           int error;
           uint32_t new;
   
           new = *(uint32_t *)arg1;
           error = sysctl_handle_int(oidp, &new, 0, req);
           if (error == 0 && req->newptr != NULL) {
                   if (new < 1)
                           error = EINVAL;
                   else
                           *(uint32_t *)arg1 = new;
           }
   
           return (error);
   }
   
   static inline uint32_t
   cdg_window_decrease(struct cc_var *ccv, unsigned long owin, unsigned int beta)
   {
   
           return ((ulmin(CCV(ccv, snd_wnd), owin) * beta) / 100);
   }
   
   /*
    * Window increase function
    * This window increase function is independent of the initial window size
    * to ensure small window flows are not discriminated against (i.e. fairness).
    * It increases at 1pkt/rtt like Reno for alpha_inc rtts, and then 2pkts/rtt for
    * the next alpha_inc rtts, etc.
    */
   static void
   cdg_window_increase(struct cc_var *ccv, int new_measurement)
   {
           struct cdg *cdg_data;
           int incr, s_w_incr;
   
           cdg_data = ccv->cc_data;
           incr = s_w_incr = 0;
   
           if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh)) {
                   /* Slow start. */
                   incr = CCV(ccv, t_maxseg);
                   s_w_incr = incr;
                   cdg_data->window_incr = cdg_data->rtt_count = 0;
           } else {
                   /* Congestion avoidance. */
                   if (new_measurement) {
                           s_w_incr = CCV(ccv, t_maxseg);
                           if (V_cdg_alpha_inc == 0) {
                                   incr = CCV(ccv, t_maxseg);
                           } else {
                                   if (++cdg_data->rtt_count >= V_cdg_alpha_inc) {
                                           cdg_data->window_incr++;
                                           cdg_data->rtt_count = 0;
                                   }
                                   incr = CCV(ccv, t_maxseg) *
                                       cdg_data->window_incr;
                           }
                   }
           }
   
           if (cdg_data->shadow_w > 0)
                   cdg_data->shadow_w = ulmin(cdg_data->shadow_w + s_w_incr,
                       TCP_MAXWIN << CCV(ccv, snd_scale));
   
           CCV(ccv, snd_cwnd) = ulmin(CCV(ccv, snd_cwnd) + incr,
               TCP_MAXWIN << CCV(ccv, snd_scale));
   }
   
   static void
   cdg_cong_signal(struct cc_var *ccv, uint32_t signal_type)
   {
           struct cdg *cdg_data = ccv->cc_data;
   
           switch(signal_type) {
           case CC_CDG_DELAY:
                   CCV(ccv, snd_ssthresh) = cdg_window_decrease(ccv,
                       CCV(ccv, snd_cwnd), V_cdg_beta_delay);
                   CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
                   CCV(ccv, snd_recover) = CCV(ccv, snd_max);
                   cdg_data->window_incr = cdg_data->rtt_count = 0;
                   ENTER_CONGRECOVERY(CCV(ccv, t_flags));
                   break;
           case CC_NDUPACK:
                   /*
                    * If already responding to congestion OR we have guessed no
                    * queue in the path is full.
                    */
                   if (IN_CONGRECOVERY(CCV(ccv, t_flags)) ||
                       cdg_data->queue_state < CDG_Q_FULL) {
                           CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
                           CCV(ccv, snd_recover) = CCV(ccv, snd_max);
                   } else {
                           /*
                            * Loss is likely to be congestion related. We have
                            * inferred a queue full state, so have shadow window
                            * react to loss as NewReno would.
                            */
                           if (cdg_data->shadow_w > 0)
                                   cdg_data->shadow_w = cdg_window_decrease(ccv,
                                       cdg_data->shadow_w, RENO_BETA);
   
                           CCV(ccv, snd_ssthresh) = max(cdg_data->shadow_w,
                               cdg_window_decrease(ccv, CCV(ccv, snd_cwnd),
                               V_cdg_beta_loss));
   
                           cdg_data->window_incr = cdg_data->rtt_count = 0;
                   }
                   ENTER_RECOVERY(CCV(ccv, t_flags));
                   break;
           default:
                   newreno_cc_cong_signal(ccv, signal_type);
                   break;
           }
   }
   
   /*
    * Using a negative exponential probabilistic backoff so that sources with
    * varying RTTs which share the same link will, on average, have the same
    * probability of backoff over time.
    *
    * Prob_backoff = 1 - exp(-qtrend / V_cdg_exp_backoff_scale), where
    * V_cdg_exp_backoff_scale is the average qtrend for the exponential backoff.
    */
   static inline int
   prob_backoff(long qtrend)
   {
           int backoff, idx, p;
   
           backoff = (qtrend > ((MAXGRAD * V_cdg_exp_backoff_scale) << D_P_E));
   
           if (!backoff) {
                   if (V_cdg_exp_backoff_scale > 1)
                           idx = (qtrend + V_cdg_exp_backoff_scale / 2) /
                               V_cdg_exp_backoff_scale;
                   else
                           idx = qtrend;
   
                   /* Backoff probability proportional to rate of queue growth. */
                   p = (INT_MAX / (1 << EXP_PREC)) * probexp[idx];
                   backoff = (random() < p);
           }
   
           return (backoff);
   }
   
   static inline void
   calc_moving_average(struct cdg *cdg_data, long qdiff_max, long qdiff_min)
   {
           struct qdiff_sample *qds;
   
           ++cdg_data->num_samples;
           if (cdg_data->num_samples > cdg_data->sample_q_size) {
                   /* Minimum RTT. */
                   qds = STAILQ_FIRST(&cdg_data->qdiffmin_q);
                   cdg_data->min_qtrend =  cdg_data->min_qtrend +
                       (qdiff_min - qds->qdiff) / cdg_data->sample_q_size;
                   STAILQ_REMOVE_HEAD(&cdg_data->qdiffmin_q, qdiff_lnk);
                   qds->qdiff = qdiff_min;
                   STAILQ_INSERT_TAIL(&cdg_data->qdiffmin_q, qds, qdiff_lnk);
   
                   /* Maximum RTT. */
                   qds = STAILQ_FIRST(&cdg_data->qdiffmax_q);
                   cdg_data->max_qtrend =  cdg_data->max_qtrend +
                       (qdiff_max - qds->qdiff) / cdg_data->sample_q_size;
                   STAILQ_REMOVE_HEAD(&cdg_data->qdiffmax_q, qdiff_lnk);
                   qds->qdiff = qdiff_max;
                   STAILQ_INSERT_TAIL(&cdg_data->qdiffmax_q, qds, qdiff_lnk);
                   --cdg_data->num_samples;
           } else {
                   qds = uma_zalloc(qdiffsample_zone, M_NOWAIT);
                   if (qds != NULL) {
                           cdg_data->min_qtrend = cdg_data->min_qtrend +
                               qdiff_min / cdg_data->sample_q_size;
                           qds->qdiff = qdiff_min;
                           STAILQ_INSERT_TAIL(&cdg_data->qdiffmin_q, qds,
                               qdiff_lnk);
                   }
   
                   qds = uma_zalloc(qdiffsample_zone, M_NOWAIT);
                   if (qds) {
                           cdg_data->max_qtrend = cdg_data->max_qtrend +
                               qdiff_max / cdg_data->sample_q_size;
                           qds->qdiff = qdiff_max;
                           STAILQ_INSERT_TAIL(&cdg_data->qdiffmax_q, qds,
                               qdiff_lnk);
                   }
           }
   }
   
   static void
   cdg_ack_received(struct cc_var *ccv, uint16_t ack_type)
   {
           struct cdg *cdg_data;
           struct ertt *e_t;
           long qdiff_max, qdiff_min;
           int congestion, new_measurement, slowstart;
   
           cdg_data = ccv->cc_data;
           e_t = (struct ertt *)khelp_get_osd(&CCV(ccv, t_osd), ertt_id);
           new_measurement = e_t->flags & ERTT_NEW_MEASUREMENT;
           congestion = 0;
           cdg_data->maxrtt_in_rtt = imax(e_t->rtt, cdg_data->maxrtt_in_rtt);
           cdg_data->minrtt_in_rtt = imin(e_t->rtt, cdg_data->minrtt_in_rtt);
   
           if (new_measurement) {
                   slowstart = (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh));
                   /*
                    * Update smoothed gradient measurements. Since we are only
                    * using one measurement per RTT, use max or min rtt_in_rtt.
                    * This is also less noisy than a sample RTT measurement. Max
                    * RTT measurements can have trouble due to OS issues.
                    */
                   if (cdg_data->maxrtt_in_prevrtt) {
                           qdiff_max = ((long)(cdg_data->maxrtt_in_rtt -
                               cdg_data->maxrtt_in_prevrtt) << D_P_E );
                           qdiff_min = ((long)(cdg_data->minrtt_in_rtt -
                               cdg_data->minrtt_in_prevrtt) << D_P_E );
   
                           if (cdg_data->sample_q_size == 0) {
                                   cdg_data->max_qtrend = qdiff_max;
                                   cdg_data->min_qtrend = qdiff_min;
                           } else
                                   calc_moving_average(cdg_data, qdiff_max, qdiff_min);
   
                           /* Probabilistic backoff with respect to gradient. */
                           if (slowstart && qdiff_min > 0)
                                   congestion = prob_backoff(qdiff_min);
                           else if (cdg_data->min_qtrend > 0)
                                   congestion = prob_backoff(cdg_data->min_qtrend);
                           else if (slowstart && qdiff_max > 0)
                                   congestion = prob_backoff(qdiff_max);
                           else if (cdg_data->max_qtrend > 0)
                                   congestion = prob_backoff(cdg_data->max_qtrend);
   
                           /* Update estimate of queue state. */
                           if (cdg_data->min_qtrend > 0 &&
                               cdg_data->max_qtrend <= 0) {
                                   cdg_data->queue_state = CDG_Q_FULL;
                           } else if (cdg_data->min_qtrend >= 0 &&
                               cdg_data->max_qtrend < 0) {
                                   cdg_data->queue_state = CDG_Q_EMPTY;
                                   cdg_data->shadow_w = 0;
                           } else if (cdg_data->min_qtrend > 0 &&
                               cdg_data->max_qtrend > 0) {
                                   cdg_data->queue_state = CDG_Q_RISING;
                           } else if (cdg_data->min_qtrend < 0 &&
                               cdg_data->max_qtrend < 0) {
                                   cdg_data->queue_state = CDG_Q_FALLING;
                           }
   
                           if (cdg_data->min_qtrend < 0 ||
                               cdg_data->max_qtrend < 0)
                                   cdg_data->consec_cong_cnt = 0;
                   }
   
                   cdg_data->minrtt_in_prevrtt = cdg_data->minrtt_in_rtt;
                   cdg_data->minrtt_in_rtt = INT_MAX;
                   cdg_data->maxrtt_in_prevrtt = cdg_data->maxrtt_in_rtt;
                   cdg_data->maxrtt_in_rtt = 0;
                   e_t->flags &= ~ERTT_NEW_MEASUREMENT;
           }
   
           if (congestion) {
                   cdg_data->consec_cong_cnt++;
                   if (!IN_RECOVERY(CCV(ccv, t_flags))) {
                           if (cdg_data->consec_cong_cnt <= V_cdg_consec_cong)
                                   cdg_cong_signal(ccv, CC_CDG_DELAY);
                           else
                                   /*
                                    * We have been backing off but the queue is not
                                    * falling. Assume we are competing with
                                    * loss-based flows and don't back off for the
                                    * next V_cdg_hold_backoff RTT periods.
                                    */
                                   if (cdg_data->consec_cong_cnt >=
                                       V_cdg_consec_cong + V_cdg_hold_backoff)
                                           cdg_data->consec_cong_cnt = 0;
   
                           /* Won't see effect until 2nd RTT. */
                           cdg_data->maxrtt_in_prevrtt = 0;
                           /*
                            * Resync shadow window in case we are competing with a
                            * loss based flow
                            */
                           cdg_data->shadow_w = ulmax(CCV(ccv, snd_cwnd),
                               cdg_data->shadow_w);
                   }
           } else if (ack_type == CC_ACK)
                   cdg_window_increase(ccv, new_measurement);
   }
   
   /* When a vnet is created and being initialised, init the per-stack CDG vars. */
   VNET_SYSINIT(cdg_init_vnet, SI_SUB_PROTO_BEGIN, SI_ORDER_FIRST,
       cdg_init_vnet, NULL);
   
   SYSCTL_DECL(_net_inet_tcp_cc_cdg);
   SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, cdg, CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
       "CAIA delay-gradient congestion control related settings");
   
   SYSCTL_STRING(_net_inet_tcp_cc_cdg, OID_AUTO, version,
       CTLFLAG_RD, CDG_VERSION, sizeof(CDG_VERSION) - 1,
       "Current algorithm/implementation version number");
   
   SYSCTL_UINT(_net_inet_tcp_cc_cdg, OID_AUTO, alpha_inc,
       CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(cdg_alpha_inc), 0,
       "Increment the window increase factor alpha by 1 MSS segment every "
       "alpha_inc RTTs during congestion avoidance mode.");
   
   SYSCTL_PROC(_net_inet_tcp_cc_cdg, OID_AUTO, beta_delay,
       CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
       &VNET_NAME(cdg_beta_delay), 70, &cdg_beta_handler, "IU",
       "Delay-based window decrease factor as a percentage "
       "(on delay-based backoff, w = w * beta_delay / 100)");
   
   SYSCTL_PROC(_net_inet_tcp_cc_cdg, OID_AUTO, beta_loss,
       CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
       &VNET_NAME(cdg_beta_loss), 50, &cdg_beta_handler, "IU",
       "Loss-based window decrease factor as a percentage "
       "(on loss-based backoff, w = w * beta_loss / 100)");
   
   SYSCTL_PROC(_net_inet_tcp_cc_cdg, OID_AUTO, exp_backoff_scale,
       CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
       &VNET_NAME(cdg_exp_backoff_scale), 2, &cdg_exp_backoff_scale_handler, "IU",
       "Scaling parameter for the probabilistic exponential backoff");
   
   SYSCTL_UINT(_net_inet_tcp_cc_cdg,  OID_AUTO, smoothing_factor,
       CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(cdg_smoothing_factor), 8,
       "Number of samples used for moving average smoothing (0 = no smoothing)");
   
   SYSCTL_UINT(_net_inet_tcp_cc_cdg, OID_AUTO, loss_compete_consec_cong,
       CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(cdg_consec_cong), 5,
       "Number of consecutive delay-gradient based congestion episodes which will "
       "trigger loss based CC compatibility");
   
   SYSCTL_UINT(_net_inet_tcp_cc_cdg, OID_AUTO, loss_compete_hold_backoff,
       CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(cdg_hold_backoff), 5,
       "Number of consecutive delay-gradient based congestion episodes to hold "
       "the window backoff for loss based CC compatibility");
   
   DECLARE_CC_MODULE(cdg, &cdg_cc_algo);
   MODULE_VERSION(cdg, 2);
   MODULE_DEPEND(cdg, ertt, 1, 1, 1);

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