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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 minumum 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, int flag)

{

        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 */

                if (tp->snd_cwnd_cnt < tp->snd_cwnd)

                        tp->snd_cwnd_cnt++;

                if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {

                        tp->snd_cwnd++;

                        tp->snd_cwnd_cnt = 0;

                }

        }

        /* 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 = {

        .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");