tcp_veno.c

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/*
 * TCP Veno congestion control
 *
 * This is based on the congestion detection/avoidance scheme described in
 *    C. P. Fu, S. C. Liew.
 *    "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
 *    IEEE Journal on Selected Areas in Communication,
 *    Feb. 2003.
 *  See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>

#include <net/tcp.h>

/* Default values of the Veno variables, in fixed-point representation
 * with V_PARAM_SHIFT bits to the right of the binary point.
 */
#define V_PARAM_SHIFT 1
static const int beta = 3 << V_PARAM_SHIFT;

/* Veno variables */
struct veno {
    u8 doing_veno_now;  /* if true, do veno for this rtt */
    u16 cntrtt;     /* # of rtts measured within last rtt */
    u32 minrtt;     /* min of rtts measured within last rtt (in usec) */
    u32 basertt;        /* the min of all Veno rtt measurements seen (in usec) */
    u32 inc;        /* decide whether to increase cwnd */
    u32 diff;       /* calculate the diff rate */
};

/* There are several situations when we must "re-start" Veno:
 *
 *  o when a connection is established
 *  o after an RTO
 *  o after fast recovery
 *  o when we send a packet and there is no outstanding
 *    unacknowledged data (restarting an idle connection)
 *
 */
static inline void veno_enable(struct sock *sk)
{
    struct veno *veno = inet_csk_ca(sk);

    /* turn on Veno */
    veno->doing_veno_now = 1;

    veno->minrtt = 0x7fffffff;
}

static inline void veno_disable(struct sock *sk)
{
    struct veno *veno = inet_csk_ca(sk);

    /* turn off Veno */
    veno->doing_veno_now = 0;
}

static void tcp_veno_init(struct sock *sk)
{
    struct veno *veno = inet_csk_ca(sk);

    veno->basertt = 0x7fffffff;
    veno->inc = 1;
    veno_enable(sk);
}

/* Do rtt sampling needed for Veno. */
static void tcp_veno_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
{
    struct veno *veno = inet_csk_ca(sk);
    u32 vrtt;

    if (rtt_us < 0)
        return;

    /* Never allow zero rtt or baseRTT */
    vrtt = rtt_us + 1;

    /* Filter to find propagation delay: */
    if (vrtt < veno->basertt)
        veno->basertt = vrtt;

    /* Find the min rtt during the last rtt to find
     * the current prop. delay + queuing delay:
     */
    veno->minrtt = min(veno->minrtt, vrtt);
    veno->cntrtt++;
}

static void tcp_veno_state(struct sock *sk, u8 ca_state)
{
    if (ca_state == TCP_CA_Open)
        veno_enable(sk);
    else
        veno_disable(sk);
}

/*
 * If the connection is idle and we are restarting,
 * then we don't want to do any Veno calculations
 * until we get fresh rtt samples.  So when we
 * restart, we reset our Veno state to a clean
 * state. After we get acks for this flight of
 * packets, _then_ we can make Veno calculations
 * again.
 */
static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
{
    if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
        tcp_veno_init(sk);
}

static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
{
    struct tcp_sock *tp = tcp_sk(sk);
    struct veno *veno = inet_csk_ca(sk);

    if (!veno->doing_veno_now) {
        tcp_reno_cong_avoid(sk, ack, in_flight);
        return;
    }

    /* limited by applications */
    if (!tcp_is_cwnd_limited(sk, in_flight))
        return;

    /* We do the Veno calculations only if we got enough rtt samples */
    if (veno->cntrtt <= 2) {
        /* We don't have enough rtt samples to do the Veno
         * calculation, so we'll behave like Reno.
         */
        tcp_reno_cong_avoid(sk, ack, in_flight);
    } else {
        u64 target_cwnd;
        u32 rtt;

        /* We have enough rtt samples, so, using the Veno
         * algorithm, we determine the state of the network.
         */

        rtt = veno->minrtt;

        target_cwnd = (tp->snd_cwnd * veno->basertt);
        target_cwnd <<= V_PARAM_SHIFT;
        do_div(target_cwnd, rtt);

        veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;

        if (tp->snd_cwnd <= tp->snd_ssthresh) {
            /* Slow start.  */
            tcp_slow_start(tp);
        } else {
            /* Congestion avoidance. */
            if (veno->diff < beta) {
                /* In the "non-congestive state", increase cwnd
                 *  every rtt.
                 */
                tcp_cong_avoid_ai(tp, tp->snd_cwnd);
            } else {
                /* In the "congestive state", increase cwnd
                 * every other rtt.
                 */
                if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
                    if (veno->inc &&
                        tp->snd_cwnd < tp->snd_cwnd_clamp) {
                        tp->snd_cwnd++;
                        veno->inc = 0;
                    } else
                        veno->inc = 1;
                    tp->snd_cwnd_cnt = 0;
                } else
                    tp->snd_cwnd_cnt++;
            }

        }
        if (tp->snd_cwnd < 2)
            tp->snd_cwnd = 2;
        else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
            tp->snd_cwnd = tp->snd_cwnd_clamp;
    }
    /* Wipe the slate clean for the next rtt. */
    /* veno->cntrtt = 0; */
    veno->minrtt = 0x7fffffff;
}

/* Veno MD phase */
static u32 tcp_veno_ssthresh(struct sock *sk)
{
    const struct tcp_sock *tp = tcp_sk(sk);
    struct veno *veno = inet_csk_ca(sk);

    if (veno->diff < beta)
        /* in "non-congestive state", cut cwnd by 1/5 */
        return max(tp->snd_cwnd * 4 / 5, 2U);
    else
        /* in "congestive state", cut cwnd by 1/2 */
        return max(tp->snd_cwnd >> 1U, 2U);
}

static struct tcp_congestion_ops tcp_veno __read_mostly = {
    .flags      = TCP_CONG_RTT_STAMP,
    .init       = tcp_veno_init,
    .ssthresh   = tcp_veno_ssthresh,
    .cong_avoid = tcp_veno_cong_avoid,
    .pkts_acked = tcp_veno_pkts_acked,
    .set_state  = tcp_veno_state,
    .cwnd_event = tcp_veno_cwnd_event,

    .owner      = THIS_MODULE,
    .name       = "veno",
};

static int __init tcp_veno_register(void)
{
    BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
    tcp_register_congestion_control(&tcp_veno);
    return 0;
}

static void __exit tcp_veno_unregister(void)
{
    tcp_unregister_congestion_control(&tcp_veno);
}

module_init(tcp_veno_register);
module_exit(tcp_veno_unregister);

MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Veno");