cc_newreno.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
 *      The Regents of the University of California.
 * Copyright (c) 2007-2008,2010,2014
 *      Swinburne University of Technology, Melbourne, Australia.
 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
 * Copyright (c) 2010 The FreeBSD Foundation
 * All rights reserved.
 *
 * This software was developed at the Centre for Advanced Internet
 * Architectures, Swinburne University of Technology, by Lawrence Stewart, James
 * Healy and David Hayes, made possible in part by a grant from the Cisco
 * University Research Program Fund at Community Foundation Silicon Valley.
 *
 * Portions of this software were developed at the Centre for Advanced
 * Internet Architectures, Swinburne University of Technology, Melbourne,
 * Australia by David Hayes under sponsorship 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.
 */
 
/*
 * This software was first released in 2007 by James Healy and Lawrence Stewart
 * whilst working on the NewTCP research project at Swinburne University of
 * Technology's Centre for Advanced Internet Architectures, Melbourne,
 * Australia, which was made possible in part by a grant from the Cisco
 * University Research Program Fund at Community Foundation Silicon Valley.
 * More details are available at:
 *   http://caia.swin.edu.au/urp/newtcp/
 *
 * Dec 2014 garmitage@swin.edu.au
 * Borrowed code fragments from cc_cdg.c to add modifiable beta
 * via sysctls.
 *
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/socket.h>
#include <sys/lock.h>
#include <sys/mutex.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/in.h>
#include <netinet/in_pcb.h>
#include <netinet/tcp.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_log_buf.h>
#include <netinet/tcp_hpts.h>
#include <netinet/cc/cc.h>
#include <netinet/cc/cc_module.h>
#include <netinet/cc/cc_newreno.h>
 
static void     newreno_cb_destroy(struct cc_var *ccv);
static void     newreno_ack_received(struct cc_var *ccv, uint16_t type);
static void     newreno_after_idle(struct cc_var *ccv);
static void     newreno_cong_signal(struct cc_var *ccv, uint32_t type);
static int newreno_ctl_output(struct cc_var *ccv, struct sockopt *sopt, void *buf);
static void     newreno_newround(struct cc_var *ccv, uint32_t round_cnt);
static void     newreno_rttsample(struct cc_var *ccv, uint32_t usec_rtt, uint32_t rxtcnt, uint32_t fas);
static  int     newreno_cb_init(struct cc_var *ccv, void *);
static size_t   newreno_data_sz(void);
 
 
VNET_DECLARE(uint32_t, newreno_beta);
#define V_newreno_beta VNET(newreno_beta)
VNET_DEFINE(uint32_t, newreno_beta_ecn) = 80;
#define V_newreno_beta_ecn VNET(newreno_beta_ecn)
 
struct cc_algo newreno_cc_algo = {
        .name = "newreno",
        .cb_destroy = newreno_cb_destroy,
        .ack_received = newreno_ack_received,
        .after_idle = newreno_after_idle,
        .cong_signal = newreno_cong_signal,
        .post_recovery = newreno_cc_post_recovery,
        .ctl_output = newreno_ctl_output,
        .newround = newreno_newround,
        .rttsample = newreno_rttsample,
        .cb_init = newreno_cb_init,
        .cc_data_sz = newreno_data_sz,
};
 
static void
newreno_log_hystart_event(struct cc_var *ccv, struct newreno *nreno, uint8_t mod, uint32_t flex1)
{
        /*
         * Types of logs (mod value)
         * 1 - rtt_thresh in flex1, checking to see if RTT is to great.
         * 2 - rtt is too great, rtt_thresh in flex1.
         * 3 - CSS is active incr in flex1
         * 4 - A new round is beginning flex1 is round count
         * 5 - A new RTT measurement flex1 is the new measurement.
         * 6 - We enter CA ssthresh is also in flex1.
         * 7 - Socket option to change hystart executed opt.val in flex1.
         * 8 - Back out of CSS into SS, flex1 is the css_baseline_minrtt
         * 9 - We enter CA, via an ECN mark.
         * 10 - We enter CA, via a loss.
         * 11 - We have slipped out of SS into CA via cwnd growth.
         * 12 - After idle has re-enabled hystart++
         */
        struct tcpcb *tp;
 
        if (hystart_bblogs == 0)
                return;
        tp = ccv->ccvc.tcp;
        if (tp->t_logstate != TCP_LOG_STATE_OFF) {
                union tcp_log_stackspecific log;
                struct timeval tv;
 
                memset(&log, 0, sizeof(log));
                log.u_bbr.flex1 = flex1;
                log.u_bbr.flex2 = nreno->css_current_round_minrtt;
                log.u_bbr.flex3 = nreno->css_lastround_minrtt;
                log.u_bbr.flex4 = nreno->css_rttsample_count;
                log.u_bbr.flex5 = nreno->css_entered_at_round;
                log.u_bbr.flex6 = nreno->css_baseline_minrtt;
                /* We only need bottom 16 bits of flags */
                log.u_bbr.flex7 = nreno->newreno_flags & 0x0000ffff;
                log.u_bbr.flex8 = mod;
                log.u_bbr.epoch = nreno->css_current_round;
                log.u_bbr.timeStamp = tcp_get_usecs(&tv);
                log.u_bbr.lt_epoch = nreno->css_fas_at_css_entry;
                log.u_bbr.pkts_out = nreno->css_last_fas;
                log.u_bbr.delivered = nreno->css_lowrtt_fas;
                log.u_bbr.pkt_epoch = ccv->flags;
                TCP_LOG_EVENTP(tp, NULL,
                    &tp->t_inpcb->inp_socket->so_rcv,
                    &tp->t_inpcb->inp_socket->so_snd,
                    TCP_HYSTART, 0,
                    0, &log, false, &tv);
        }
}
 
static size_t
newreno_data_sz(void)
{
        return (sizeof(struct newreno));
}
 
static int
newreno_cb_init(struct cc_var *ccv, void *ptr)
{
        struct newreno *nreno;
 
        INP_WLOCK_ASSERT(ccv->ccvc.tcp->t_inpcb);
        if (ptr == NULL) {
                ccv->cc_data = malloc(sizeof(struct newreno), M_CC_MEM, M_NOWAIT);
                if (ccv->cc_data == NULL)
                        return (ENOMEM);
        } else
                ccv->cc_data = ptr;
        nreno = (struct newreno *)ccv->cc_data;
        /* NB: nreno is not zeroed, so initialise all fields. */
        nreno->beta = V_newreno_beta;
        nreno->beta_ecn = V_newreno_beta_ecn;
        /*
         * We set the enabled flag so that if
         * the socket option gets strobed and
         * we have not hit a loss
         */
        nreno->newreno_flags = CC_NEWRENO_HYSTART_ENABLED;
        /* At init set both to infinity */
        nreno->css_lastround_minrtt = 0xffffffff;
        nreno->css_current_round_minrtt = 0xffffffff;
        nreno->css_current_round = 0;
        nreno->css_baseline_minrtt = 0xffffffff;
        nreno->css_rttsample_count = 0;
        nreno->css_entered_at_round = 0;
        nreno->css_fas_at_css_entry = 0;
        nreno->css_lowrtt_fas = 0;
        nreno->css_last_fas = 0;
        return (0);
}
 
static void
newreno_cb_destroy(struct cc_var *ccv)
{
        free(ccv->cc_data, M_CC_MEM);
}
 
static void
newreno_ack_received(struct cc_var *ccv, uint16_t type)
{
        struct newreno *nreno;
 
        nreno = ccv->cc_data;
        if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
            (ccv->flags & CCF_CWND_LIMITED)) {
                u_int cw = CCV(ccv, snd_cwnd);
                u_int incr = CCV(ccv, t_maxseg);
 
                /*
                 * Regular in-order ACK, open the congestion window.
                 * Method depends on which congestion control state we're
                 * in (slow start or cong avoid) and if ABC (RFC 3465) is
                 * enabled.
                 *
                 * slow start: cwnd <= ssthresh
                 * cong avoid: cwnd > ssthresh
                 *
                 * slow start and ABC (RFC 3465):
                 *   Grow cwnd exponentially by the amount of data
                 *   ACKed capping the max increment per ACK to
                 *   (abc_l_var * maxseg) bytes.
                 *
                 * slow start without ABC (RFC 5681):
                 *   Grow cwnd exponentially by maxseg per ACK.
                 *
                 * cong avoid and ABC (RFC 3465):
                 *   Grow cwnd linearly by maxseg per RTT for each
                 *   cwnd worth of ACKed data.
                 *
                 * cong avoid without ABC (RFC 5681):
                 *   Grow cwnd linearly by approximately maxseg per RTT using
                 *   maxseg^2 / cwnd per ACK as the increment.
                 *   If cwnd > maxseg^2, fix the cwnd increment at 1 byte to
                 *   avoid capping cwnd.
                 */
                if (cw > CCV(ccv, snd_ssthresh)) {
                        if (nreno->newreno_flags & CC_NEWRENO_HYSTART_IN_CSS) {
                                /*
                                 * We have slipped into CA with
                                 * CSS active. Deactivate all.
                                 */
                                /* Turn off the CSS flag */
                                nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_IN_CSS;
                                /* Disable use of CSS in the future except long idle  */
                                nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_ENABLED;
                                newreno_log_hystart_event(ccv, nreno, 11, CCV(ccv, snd_ssthresh));
                        }
                        if (V_tcp_do_rfc3465) {
                                if (ccv->flags & CCF_ABC_SENTAWND)
                                        ccv->flags &= ~CCF_ABC_SENTAWND;
                                else
                                        incr = 0;
                        } else
                                incr = max((incr * incr / cw), 1);
                } else if (V_tcp_do_rfc3465) {
                        /*
                         * In slow-start with ABC enabled and no RTO in sight?
                         * (Must not use abc_l_var > 1 if slow starting after
                         * an RTO. On RTO, snd_nxt = snd_una, so the
                         * snd_nxt == snd_max check is sufficient to
                         * handle this).
                         *
                         * XXXLAS: Find a way to signal SS after RTO that
                         * doesn't rely on tcpcb vars.
                         */
                        uint16_t abc_val;
 
                        if (ccv->flags & CCF_USE_LOCAL_ABC)
                                abc_val = ccv->labc;
                        else
                                abc_val = V_tcp_abc_l_var;
                        if ((ccv->flags & CCF_HYSTART_ALLOWED) &&
                            (nreno->newreno_flags & CC_NEWRENO_HYSTART_ENABLED) &&
                            ((nreno->newreno_flags & CC_NEWRENO_HYSTART_IN_CSS) == 0)) {
                                /*
                                 * Hystart is allowed and still enabled and we are not yet
                                 * in CSS. Lets check to see if we can make a decision on
                                 * if we need to go into CSS.
                                 */
                                if ((nreno->css_rttsample_count >= hystart_n_rttsamples) &&
                                    (nreno->css_current_round_minrtt != 0xffffffff) &&
                                    (nreno->css_lastround_minrtt != 0xffffffff)) {
                                        uint32_t rtt_thresh;
 
                                        /* Clamp (minrtt_thresh, lastround/8, maxrtt_thresh) */
                                        rtt_thresh = (nreno->css_lastround_minrtt >> 3);
                                        if (rtt_thresh < hystart_minrtt_thresh)
                                                rtt_thresh = hystart_minrtt_thresh;
                                        if (rtt_thresh > hystart_maxrtt_thresh)
                                                rtt_thresh = hystart_maxrtt_thresh;
                                        newreno_log_hystart_event(ccv, nreno, 1, rtt_thresh);
                                        if (nreno->css_current_round_minrtt >= (nreno->css_lastround_minrtt + rtt_thresh)) {
                                                /* Enter CSS */
                                                nreno->newreno_flags |= CC_NEWRENO_HYSTART_IN_CSS;
                                                nreno->css_fas_at_css_entry = nreno->css_lowrtt_fas;
                                                /*
                                                 * The draft (v4) calls for us to set baseline to css_current_round_min
                                                 * but that can cause an oscillation. We probably shoudl be using
                                                 * css_lastround_minrtt, but the authors insist that will cause
                                                 * issues on exiting early. We will leave the draft version for now
                                                 * but I suspect this is incorrect.
                                                 */
                                                nreno->css_baseline_minrtt = nreno->css_current_round_minrtt;
                                                nreno->css_entered_at_round = nreno->css_current_round;
                                                newreno_log_hystart_event(ccv, nreno, 2, rtt_thresh);
                                        }
                                }
                        }
                        if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
                                incr = min(ccv->bytes_this_ack,
                                    ccv->nsegs * abc_val *
                                    CCV(ccv, t_maxseg));
                        else
                                incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
 
                        /* Only if Hystart is enabled will the flag get set */
                        if (nreno->newreno_flags & CC_NEWRENO_HYSTART_IN_CSS) {
                                incr /= hystart_css_growth_div;
                                newreno_log_hystart_event(ccv, nreno, 3, incr);
                        }
                }
                /* ABC is on by default, so incr equals 0 frequently. */
                if (incr > 0)
                        CCV(ccv, snd_cwnd) = min(cw + incr,
                            TCP_MAXWIN << CCV(ccv, snd_scale));
        }
}
 
static void
newreno_after_idle(struct cc_var *ccv)
{
        struct newreno *nreno;
 
        nreno = ccv->cc_data;
        newreno_cc_after_idle(ccv);
        if ((nreno->newreno_flags & CC_NEWRENO_HYSTART_ENABLED) == 0) {
                /*
                 * Re-enable hystart if we have been idle.
                 */
                nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_IN_CSS;
                nreno->newreno_flags |= CC_NEWRENO_HYSTART_ENABLED;
                newreno_log_hystart_event(ccv, nreno, 12, CCV(ccv, snd_ssthresh));
        }
}
 
/*
 * Perform any necessary tasks before we enter congestion recovery.
 */
static void
newreno_cong_signal(struct cc_var *ccv, uint32_t type)
{
        struct newreno *nreno;
        uint32_t beta, beta_ecn, cwin, factor;
        u_int mss;
 
        cwin = CCV(ccv, snd_cwnd);
        mss = tcp_fixed_maxseg(ccv->ccvc.tcp);
        nreno = ccv->cc_data;
        beta = (nreno == NULL) ? V_newreno_beta : nreno->beta;;
        beta_ecn = (nreno == NULL) ? V_newreno_beta_ecn : nreno->beta_ecn;
        /*
         * Note that we only change the backoff for ECN if the
         * global sysctl V_cc_do_abe is set <or> the stack itself
         * has set a flag in our newreno_flags (due to pacing) telling
         * us to use the lower valued back-off.
         */
        if ((type == CC_ECN) &&
            (V_cc_do_abe ||
            ((nreno != NULL) && (nreno->newreno_flags & CC_NEWRENO_BETA_ECN_ENABLED))))
                factor = beta_ecn;
        else
                factor = beta;
 
        /* Catch algos which mistakenly leak private signal types. */
        KASSERT((type & CC_SIGPRIVMASK) == 0,
            ("%s: congestion signal type 0x%08x is private\n", __func__, type));
 
        cwin = max(((uint64_t)cwin * (uint64_t)factor) / (100ULL * (uint64_t)mss),
            2) * mss;
 
        switch (type) {
        case CC_NDUPACK:
                if (nreno->newreno_flags & CC_NEWRENO_HYSTART_ENABLED) {
                        /* Make sure the flags are all off we had a loss */
                        nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_ENABLED;
                        nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_IN_CSS;
                        newreno_log_hystart_event(ccv, nreno, 10, CCV(ccv, snd_ssthresh));
                }
                if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
                        if (IN_CONGRECOVERY(CCV(ccv, t_flags) &&
                            V_cc_do_abe && V_cc_abe_frlossreduce)) {
                                CCV(ccv, snd_ssthresh) =
                                    ((uint64_t)CCV(ccv, snd_ssthresh) *
                                     (uint64_t)beta) / (uint64_t)beta_ecn;
                        }
                        if (!IN_CONGRECOVERY(CCV(ccv, t_flags)))
                                CCV(ccv, snd_ssthresh) = cwin;
                        ENTER_RECOVERY(CCV(ccv, t_flags));
                }
                break;
        case CC_ECN:
                if (nreno->newreno_flags & CC_NEWRENO_HYSTART_ENABLED) {
                        /* Make sure the flags are all off we had a loss */
                        nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_ENABLED;
                        nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_IN_CSS;
                        newreno_log_hystart_event(ccv, nreno, 9, CCV(ccv, snd_ssthresh));
                }
                if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
                        CCV(ccv, snd_ssthresh) = cwin;
                        CCV(ccv, snd_cwnd) = cwin;
                        ENTER_CONGRECOVERY(CCV(ccv, t_flags));
                }
                break;
        case CC_RTO:
                CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd),
                                                 CCV(ccv, snd_cwnd)) / 2 / mss,
                                             2) * mss;
                CCV(ccv, snd_cwnd) = mss;
                break;
        }
}
 
static int
newreno_ctl_output(struct cc_var *ccv, struct sockopt *sopt, void *buf)
{
        struct newreno *nreno;
        struct cc_newreno_opts *opt;
 
        if (sopt->sopt_valsize != sizeof(struct cc_newreno_opts))
                return (EMSGSIZE);
 
        if (CC_ALGO(ccv->ccvc.tcp) != &newreno_cc_algo)
                return (ENOPROTOOPT);
 
        nreno = (struct newreno *)ccv->cc_data;
        opt = buf;
        switch (sopt->sopt_dir) {
        case SOPT_SET:
                switch (opt->name) {
                case CC_NEWRENO_BETA:
                        nreno->beta = opt->val;
                        break;
                case CC_NEWRENO_BETA_ECN:
                        if ((!V_cc_do_abe) && ((nreno->newreno_flags & CC_NEWRENO_BETA_ECN) == 0))
                                return (EACCES);
                        nreno->beta_ecn = opt->val;
                        nreno->newreno_flags |= CC_NEWRENO_BETA_ECN_ENABLED;
                        break;
                default:
                        return (ENOPROTOOPT);
                }
                break;
        case SOPT_GET:
                switch (opt->name) {
                case CC_NEWRENO_BETA:
                        opt->val = (nreno == NULL) ?
                            V_newreno_beta : nreno->beta;
                        break;
                case CC_NEWRENO_BETA_ECN:
                        opt->val = (nreno == NULL) ?
                            V_newreno_beta_ecn : nreno->beta_ecn;
                        break;
                default:
                        return (ENOPROTOOPT);
                }
                break;
        default:
                return (EINVAL);
        }
 
        return (0);
}
 
static int
newreno_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 (arg1 == &VNET_NAME(newreno_beta_ecn) && !V_cc_do_abe)
                        error = EACCES;
                else if (new == 0 || new > 100)
                        error = EINVAL;
                else
                        *(uint32_t *)arg1 = new;
        }
 
        return (error);
}
 
static void
newreno_newround(struct cc_var *ccv, uint32_t round_cnt)
{
        struct newreno *nreno;
 
        nreno = (struct newreno *)ccv->cc_data;
        /* We have entered a new round */
        nreno->css_lastround_minrtt = nreno->css_current_round_minrtt;
        nreno->css_current_round_minrtt = 0xffffffff;
        nreno->css_rttsample_count = 0;
        nreno->css_current_round = round_cnt;
        if ((nreno->newreno_flags & CC_NEWRENO_HYSTART_IN_CSS) &&
            ((round_cnt - nreno->css_entered_at_round) >= hystart_css_rounds)) {
                /* Enter CA */
                if (ccv->flags & CCF_HYSTART_CAN_SH_CWND) {
                        /*
                         * We engage more than snd_ssthresh, engage
                         * the brakes!! Though we will stay in SS to
                         * creep back up again, so lets leave CSS active
                         * and give us hystart_css_rounds more rounds.
                         */
                        if (ccv->flags & CCF_HYSTART_CONS_SSTH) {
                                CCV(ccv, snd_ssthresh) = ((nreno->css_lowrtt_fas + nreno->css_fas_at_css_entry) / 2);
                        } else {
                                CCV(ccv, snd_ssthresh) = nreno->css_lowrtt_fas;
                        }
                        CCV(ccv, snd_cwnd) = nreno->css_fas_at_css_entry;
                        nreno->css_entered_at_round = round_cnt;
                } else {
                        CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
                        /* Turn off the CSS flag */
                        nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_IN_CSS;
                        /* Disable use of CSS in the future except long idle  */
                        nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_ENABLED;
                }
                newreno_log_hystart_event(ccv, nreno, 6, CCV(ccv, snd_ssthresh));
        }
        if (nreno->newreno_flags & CC_NEWRENO_HYSTART_ENABLED)
                newreno_log_hystart_event(ccv, nreno, 4, round_cnt);
}
 
static void
newreno_rttsample(struct cc_var *ccv, uint32_t usec_rtt, uint32_t rxtcnt, uint32_t fas)
{
        struct newreno *nreno;
 
        nreno = (struct newreno *)ccv->cc_data;
        if (rxtcnt > 1) {
                /*
                 * Only look at RTT's that are non-ambiguous.
                 */
                return;
        }
        nreno->css_rttsample_count++;
        nreno->css_last_fas = fas;
        if (nreno->css_current_round_minrtt > usec_rtt) {
                nreno->css_current_round_minrtt = usec_rtt;
                nreno->css_lowrtt_fas = nreno->css_last_fas;
        }
        if ((nreno->css_rttsample_count >= hystart_n_rttsamples) &&
            (nreno->css_current_round_minrtt != 0xffffffff) &&
            (nreno->css_lastround_minrtt != 0xffffffff)) {
                /*
                 * We were in CSS and the RTT is now less, we
                 * entered CSS erroneously.
                 */
                nreno->newreno_flags &= ~CC_NEWRENO_HYSTART_IN_CSS;
                newreno_log_hystart_event(ccv, nreno, 8, nreno->css_baseline_minrtt);
                nreno->css_baseline_minrtt = 0xffffffff;
        }
        if (nreno->newreno_flags & CC_NEWRENO_HYSTART_ENABLED)
                newreno_log_hystart_event(ccv, nreno, 5, usec_rtt);
}
 
SYSCTL_DECL(_net_inet_tcp_cc_newreno);
SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, newreno,
    CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
    "New Reno related settings");
 
SYSCTL_PROC(_net_inet_tcp_cc_newreno, OID_AUTO, beta,
    CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    &VNET_NAME(newreno_beta), 3, &newreno_beta_handler, "IU",
    "New Reno beta, specified as number between 1 and 100");
 
SYSCTL_PROC(_net_inet_tcp_cc_newreno, OID_AUTO, beta_ecn,
    CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    &VNET_NAME(newreno_beta_ecn), 3, &newreno_beta_handler, "IU",
    "New Reno beta ecn, specified as number between 1 and 100");
 
DECLARE_CC_MODULE(newreno, &newreno_cc_algo);
MODULE_VERSION(newreno, 2);