tcp_yeah.c

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/*
 *
 *   YeAH TCP
 *
 * For further details look at:
 *    http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
 *
 */
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>

#include <net/tcp.h>

#include "tcp_vegas.h"

#define TCP_YEAH_ALPHA       80 //lin number of packets queued at the bottleneck
#define TCP_YEAH_GAMMA        1 //lin fraction of queue to be removed per rtt
#define TCP_YEAH_DELTA        3 //log minimum fraction of cwnd to be removed on loss
#define TCP_YEAH_EPSILON      1 //log maximum fraction to be removed on early decongestion
#define TCP_YEAH_PHY          8 //lin maximum delta from base
#define TCP_YEAH_RHO         16 //lin minimum number of consecutive rtt to consider competition on loss
#define TCP_YEAH_ZETA        50 //lin minimum number of state switchs to reset reno_count

#define TCP_SCALABLE_AI_CNT  100U

/* YeAH variables */
struct yeah {
    struct vegas vegas; /* must be first */

    /* YeAH */
    u32 lastQ;
    u32 doing_reno_now;

    u32 reno_count;
    u32 fast_count;

    u32 pkts_acked;
};

static void tcp_yeah_init(struct sock *sk)
{
    struct tcp_sock *tp = tcp_sk(sk);
    struct yeah *yeah = inet_csk_ca(sk);

    tcp_vegas_init(sk);

    yeah->doing_reno_now = 0;
    yeah->lastQ = 0;

    yeah->reno_count = 2;

    /* Ensure the MD arithmetic works.  This is somewhat pedantic,
     * since I don't think we will see a cwnd this large. :) */
    tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);

}


static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked, s32 rtt_us)
{
    const struct inet_connection_sock *icsk = inet_csk(sk);
    struct yeah *yeah = inet_csk_ca(sk);

    if (icsk->icsk_ca_state == TCP_CA_Open)
        yeah->pkts_acked = pkts_acked;

    tcp_vegas_pkts_acked(sk, pkts_acked, rtt_us);
}

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

    if (!tcp_is_cwnd_limited(sk, in_flight))
        return;

    if (tp->snd_cwnd <= tp->snd_ssthresh)
        tcp_slow_start(tp);

    else if (!yeah->doing_reno_now) {
        /* Scalable */

        tp->snd_cwnd_cnt += yeah->pkts_acked;
        if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
            if (tp->snd_cwnd < tp->snd_cwnd_clamp)
                tp->snd_cwnd++;
            tp->snd_cwnd_cnt = 0;
        }

        yeah->pkts_acked = 1;

    } else {
        /* Reno */
        tcp_cong_avoid_ai(tp, tp->snd_cwnd);
    }

    /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
     *
     * These are so named because they represent the approximate values
     * of snd_una and snd_nxt at the beginning of the current RTT. More
     * precisely, they represent the amount of data sent during the RTT.
     * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
     * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding
     * bytes of data have been ACKed during the course of the RTT, giving
     * an "actual" rate of:
     *
     *     (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration)
     *
     * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una,
     * because delayed ACKs can cover more than one segment, so they
     * don't line up yeahly with the boundaries of RTTs.
     *
     * Another unfortunate fact of life is that delayed ACKs delay the
     * advance of the left edge of our send window, so that the number
     * of bytes we send in an RTT is often less than our cwnd will allow.
     * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
     */

    if (after(ack, yeah->vegas.beg_snd_nxt)) {

        /* We do the Vegas calculations only if we got enough RTT
         * samples that we can be reasonably sure that we got
         * at least one RTT sample that wasn't from a delayed ACK.
         * If we only had 2 samples total,
         * then that means we're getting only 1 ACK per RTT, which
         * means they're almost certainly delayed ACKs.
         * If  we have 3 samples, we should be OK.
         */

        if (yeah->vegas.cntRTT > 2) {
            u32 rtt, queue;
            u64 bw;

            /* We have enough RTT samples, so, using the Vegas
             * algorithm, we determine if we should increase or
             * decrease cwnd, and by how much.
             */

            /* Pluck out the RTT we are using for the Vegas
             * calculations. This is the min RTT seen during the
             * last RTT. Taking the min filters out the effects
             * of delayed ACKs, at the cost of noticing congestion
             * a bit later.
             */
            rtt = yeah->vegas.minRTT;

            /* Compute excess number of packets above bandwidth
             * Avoid doing full 64 bit divide.
             */
            bw = tp->snd_cwnd;
            bw *= rtt - yeah->vegas.baseRTT;
            do_div(bw, rtt);
            queue = bw;

            if (queue > TCP_YEAH_ALPHA ||
                rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
                if (queue > TCP_YEAH_ALPHA &&
                    tp->snd_cwnd > yeah->reno_count) {
                    u32 reduction = min(queue / TCP_YEAH_GAMMA ,
                                tp->snd_cwnd >> TCP_YEAH_EPSILON);

                    tp->snd_cwnd -= reduction;

                    tp->snd_cwnd = max(tp->snd_cwnd,
                               yeah->reno_count);

                    tp->snd_ssthresh = tp->snd_cwnd;
                }

                if (yeah->reno_count <= 2)
                    yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
                else
                    yeah->reno_count++;

                yeah->doing_reno_now = min(yeah->doing_reno_now + 1,
                               0xffffffU);
            } else {
                yeah->fast_count++;

                if (yeah->fast_count > TCP_YEAH_ZETA) {
                    yeah->reno_count = 2;
                    yeah->fast_count = 0;
                }

                yeah->doing_reno_now = 0;
            }

            yeah->lastQ = queue;

        }

        /* Save the extent of the current window so we can use this
         * at the end of the next RTT.
         */
        yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
        yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
        yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;

        /* Wipe the slate clean for the next RTT. */
        yeah->vegas.cntRTT = 0;
        yeah->vegas.minRTT = 0x7fffffff;
    }
}

static u32 tcp_yeah_ssthresh(struct sock *sk) {
    const struct tcp_sock *tp = tcp_sk(sk);
    struct yeah *yeah = inet_csk_ca(sk);
    u32 reduction;

    if (yeah->doing_reno_now < TCP_YEAH_RHO) {
        reduction = yeah->lastQ;

        reduction = min( reduction, max(tp->snd_cwnd>>1, 2U) );

        reduction = max( reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
    } else
        reduction = max(tp->snd_cwnd>>1, 2U);

    yeah->fast_count = 0;
    yeah->reno_count = max(yeah->reno_count>>1, 2U);

    return tp->snd_cwnd - reduction;
}

static struct tcp_congestion_ops tcp_yeah __read_mostly = {
    .flags      = TCP_CONG_RTT_STAMP,
    .init       = tcp_yeah_init,
    .ssthresh   = tcp_yeah_ssthresh,
    .cong_avoid = tcp_yeah_cong_avoid,
    .min_cwnd   = tcp_reno_min_cwnd,
    .set_state  = tcp_vegas_state,
    .cwnd_event = tcp_vegas_cwnd_event,
    .get_info   = tcp_vegas_get_info,
    .pkts_acked = tcp_yeah_pkts_acked,

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

static int __init tcp_yeah_register(void)
{
    BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
    tcp_register_congestion_control(&tcp_yeah);
    return 0;
}

static void __exit tcp_yeah_unregister(void)
{
    tcp_unregister_congestion_control(&tcp_yeah);
}

module_init(tcp_yeah_register);
module_exit(tcp_yeah_unregister);

MODULE_AUTHOR("Angelo P. Castellani");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("YeAH TCP");