xnu-2782.10.72.tar.gz

[apple/xnu.git] / bsd / netinet / tcp_newreno.c

/*
 * Copyright (c) 2010-2014 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
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 * This file contains Original Code and/or Modifications of Original Code
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 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
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/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
 * $FreeBSD: src/sys/netinet/tcp_input.c,v 1.107.2.16 2001/08/22 00:59:12 silby Exp $
 */
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/protosw.h>
#include <sys/socketvar.h>

#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>

#if INET6
#include <netinet/ip6.h>
#endif
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#include <netinet/tcp_cc.h>
#include <libkern/OSAtomic.h>

int tcp_newreno_init(struct tcpcb *tp);
int tcp_newreno_cleanup(struct tcpcb *tp);
void tcp_newreno_cwnd_init_or_reset(struct tcpcb *tp);
void tcp_newreno_congestion_avd(struct tcpcb *tp, struct tcphdr *th);
void tcp_newreno_ack_rcvd(struct tcpcb *tp, struct tcphdr *th);
void tcp_newreno_pre_fr(struct tcpcb *tp);
void tcp_newreno_post_fr(struct tcpcb *tp, struct tcphdr *th);
void tcp_newreno_after_idle(struct tcpcb *tp);
void tcp_newreno_after_timeout(struct tcpcb *tp);
int tcp_newreno_delay_ack(struct tcpcb *tp, struct tcphdr *th);
void tcp_newreno_switch_cc(struct tcpcb *tp, uint16_t old_index);

struct tcp_cc_algo tcp_cc_newreno = {
        .name = "newreno",
        .init = tcp_newreno_init,
        .cleanup = tcp_newreno_cleanup,
        .cwnd_init = tcp_newreno_cwnd_init_or_reset,
        .congestion_avd = tcp_newreno_congestion_avd,
        .ack_rcvd = tcp_newreno_ack_rcvd,
        .pre_fr = tcp_newreno_pre_fr,
        .post_fr = tcp_newreno_post_fr,
        .after_idle = tcp_newreno_cwnd_init_or_reset,
        .after_timeout = tcp_newreno_after_timeout,
        .delay_ack = tcp_newreno_delay_ack,
        .switch_to = tcp_newreno_switch_cc
};

int tcp_newreno_init(struct tcpcb *tp) {
#pragma unused(tp)
        OSIncrementAtomic((volatile SInt32 *)&tcp_cc_newreno.num_sockets);
        return 0;
}

int tcp_newreno_cleanup(struct tcpcb *tp) {
#pragma unused(tp)
        OSDecrementAtomic((volatile SInt32 *)&tcp_cc_newreno.num_sockets);
        return 0;
}

/* Initialize the congestion window for a connection or
 * handles connections that have been idle for
 * some time. In this state, no acks are
 * expected to clock out any data we send --
 * slow start to get ack "clock" running again.
 *
 * Set the slow-start flight size depending on whether
 * this is a local network or not.
 */
void
tcp_newreno_cwnd_init_or_reset(struct tcpcb *tp) {
        tcp_cc_cwnd_init_or_reset(tp);

        /* If stretch ack was auto disabled, re-evaluate the situation */
        tcp_cc_after_idle_stretchack(tp);
}


/* Function to handle an in-sequence ack during congestion avoidance phase.
 * This will get called from header prediction code.
 */
void
tcp_newreno_congestion_avd(struct tcpcb *tp, struct tcphdr *th) {
        uint32_t acked = 0;
        acked = BYTES_ACKED(th, tp);
        /*
         * Grow the congestion window, if the
         * connection is cwnd bound.
         */
        if (tp->snd_cwnd < tp->snd_wnd) {
                tp->t_bytes_acked += acked;
                if (tp->t_bytes_acked > tp->snd_cwnd) {
                        tp->t_bytes_acked -= tp->snd_cwnd;
                        tp->snd_cwnd += tp->t_maxseg;
                }
        }
}
/* Function to process an ack.
 */
void
tcp_newreno_ack_rcvd(struct tcpcb *tp, struct tcphdr *th) {
        /*
         * RFC 3465 - Appropriate Byte Counting.
         *
         * If the window is currently less than ssthresh,
         * open the window by the number of bytes ACKed by
         * the last ACK, however clamp the window increase
         * to an upper limit "L".
         *
         * In congestion avoidance phase, open the window by
         * one segment each time "bytes_acked" grows to be
         * greater than or equal to the congestion window.
         */

        register u_int cw = tp->snd_cwnd;
        register u_int incr = tp->t_maxseg;
        int acked = 0;

        acked = BYTES_ACKED(th, tp);
        if (tcp_do_rfc3465) {

                if (cw >= tp->snd_ssthresh) {
                        tp->t_bytes_acked += acked;
                        if (tp->t_bytes_acked >= cw) {
                                /* Time to increase the window. */
                                tp->t_bytes_acked -= cw;
                        } else {
                                /* No need to increase yet. */
                                incr = 0;
                        }
                } else {
                        /*
                         * If the user explicitly enables RFC3465
                         * use 2*SMSS for the "L" param.  Otherwise
                         * use the more conservative 1*SMSS.
                         *
                         * (See RFC 3465 2.3 Choosing the Limit)
                         */
                        uint32_t abc_lim;
                        abc_lim = (tcp_do_rfc3465_lim2 &&
                                tp->snd_nxt == tp->snd_max) ? incr * 2 
                                : incr;

                        incr = lmin(acked, abc_lim);
                }
        } else {
                /*
                 * If the window gives us less than ssthresh packets
                 * in flight, open exponentially (segsz per packet).
                 * Otherwise open linearly: segsz per window
                 * (segsz^2 / cwnd per packet).
                 */

                if (cw >= tp->snd_ssthresh)
                        incr = max((incr * incr / cw), 1);
        }
        tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
}

void
tcp_newreno_pre_fr(struct tcpcb *tp) {

        uint32_t win;

        win = min(tp->snd_wnd, tp->snd_cwnd) / 
                2 / tp->t_maxseg;
        if ( win < 2 )
                win = 2;
        tp->snd_ssthresh = win * tp->t_maxseg; 
        tcp_cc_resize_sndbuf(tp);

}

void
tcp_newreno_post_fr(struct tcpcb *tp, struct tcphdr *th) {
        int32_t ss;

        ss = tp->snd_max - th->th_ack;

        /*
         * Complete ack.  Inflate the congestion window to
         * ssthresh and exit fast recovery.
         *
         * Window inflation should have left us with approx.
         * snd_ssthresh outstanding data.  But in case we
         * would be inclined to send a burst, better to do
         * it via the slow start mechanism.
         *
         * If the flight size is zero, then make congestion 
         * window to be worth at least 2 segments to avoid 
         * delayed acknowledgement (draft-ietf-tcpm-rfc3782-bis-05).
         */
        if (ss < (int32_t)tp->snd_ssthresh)
                tp->snd_cwnd = max(ss, tp->t_maxseg) + tp->t_maxseg;
        else
                tp->snd_cwnd = tp->snd_ssthresh;
        tp->t_bytes_acked = 0;
}

/* Function to change the congestion window when the retransmit 
 * timer fires.
 */
void
tcp_newreno_after_timeout(struct tcpcb *tp) {
        /*
         * Close the congestion window down to one segment
         * (we'll open it by one segment for each ack we get).
         * Since we probably have a window's worth of unacked
         * data accumulated, this "slow start" keeps us from
         * dumping all that data as back-to-back packets (which
         * might overwhelm an intermediate gateway).
         *
         * There are two phases to the opening: Initially we
         * open by one mss on each ack.  This makes the window
         * size increase exponentially with time.  If the
         * window is larger than the path can handle, this
         * exponential growth results in dropped packet(s)
         * almost immediately.  To get more time between
         * drops but still "push" the network to take advantage
         * of improving conditions, we switch from exponential
         * to linear window opening at some threshhold size.
         * For a threshhold, we use half the current window
         * size, truncated to a multiple of the mss.
         *
         * (the minimum cwnd that will give us exponential
         * growth is 2 mss.  We don't allow the threshhold
         * to go below this.)
         */
        if (tp->t_state >=  TCPS_ESTABLISHED) {
                u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
                if (win < 2)
                        win = 2;
                tp->snd_ssthresh = win * tp->t_maxseg;

                tp->snd_cwnd = tp->t_maxseg;
                tcp_cc_resize_sndbuf(tp);
        }
}

/*
 * Indicate whether this ack should be delayed.
 * We can delay the ack if:
 *  - delayed acks are enabled and set to 1, same as when value is set to 2. 
 *    We kept this for binary compatibility.
 *  - delayed acks are enabled and set to 2, will "ack every other packet"
 *      - if our last ack wasn't a 0-sized window.
 *      - if the peer hasn't sent us a TH_PUSH data packet (this solves 3649245). 
 *              If TH_PUSH is set, take this as a clue that we need to ACK 
 *              with no delay. This helps higher level protocols who won't send
 *              us more data even if the window is open because their 
 *              last "segment" hasn't been ACKed
 *  - delayed acks are enabled and set to 3,  will do "streaming detection" 
 *    (see the comment in tcp_input.c) and
 *      - if we receive more than "maxseg_unacked" full packets in the last 100ms
 *      - if the connection is not in slow-start or idle or loss/recovery states
 *      - if those criteria aren't met, it will ack every other packet.
 */

int
tcp_newreno_delay_ack(struct tcpcb *tp, struct tcphdr *th) {
        return (tcp_cc_delay_ack(tp, th));
}

/* Switch to newreno from a different CC. If the connection is in
 * congestion avoidance state, it can continue to use the current
 * congestion window because it is going to be conservative. But
 * if the connection is in slow-start, we will halve the congestion
 * window and let newreno work from there. 
 */
void
tcp_newreno_switch_cc(struct tcpcb *tp, uint16_t old_index) {
#pragma unused(old_index)

        uint32_t cwnd = min(tp->snd_wnd, tp->snd_cwnd);
        if (tp->snd_cwnd >= tp->snd_ssthresh) {
                cwnd = cwnd / tp->t_maxseg;
        } else { 
                cwnd = cwnd / 2 / tp->t_maxseg;
        }
        tp->snd_cwnd = max(TCP_CC_CWND_INIT_BYTES, cwnd * tp->t_maxseg);

        /* Start counting bytes for RFC 3465 again */
        tp->t_bytes_acked = 0;

        OSIncrementAtomic((volatile SInt32 *)&tcp_cc_newreno.num_sockets);
}