Subversion Repositories test_project

/*

 * TCP Vegas congestion control

 *

 * This is based on the congestion detection/avoidance scheme described in

 *    Lawrence S. Brakmo and Larry L. Peterson.

 *    "TCP Vegas: End to end congestion avoidance on a global internet."

 *    IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,

 *    October 1995. Available from:

 *      ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps

 *

 * See http://www.cs.arizona.edu/xkernel/ for their implementation.

 * The main aspects that distinguish this implementation from the

 * Arizona Vegas implementation are:

 *   o We do not change the loss detection or recovery mechanisms of

 *     Linux in any way. Linux already recovers from losses quite well,

 *     using fine-grained timers, NewReno, and FACK.

 *   o To avoid the performance penalty imposed by increasing cwnd

 *     only every-other RTT during slow start, we increase during

 *     every RTT during slow start, just like Reno.

 *   o Largely to allow continuous cwnd growth during slow start,

 *     we use the rate at which ACKs come back as the "actual"

 *     rate, rather than the rate at which data is sent.

 *   o To speed convergence to the right rate, we set the cwnd

 *     to achieve the right ("actual") rate when we exit slow start.

 *   o To filter out the noise caused by delayed ACKs, we use the

 *     minimum RTT sample observed during the last RTT to calculate

 *     the actual rate.

 *   o When the sender re-starts from idle, it waits until it has

 *     received ACKs for an entire flight of new data before making

 *     a cwnd adjustment decision. The original Vegas implementation

 *     assumed senders never went idle.

 */

#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"

/* Default values of the Vegas variables, in fixed-point representation

 * with V_PARAM_SHIFT bits to the right of the binary point.

 */

#define V_PARAM_SHIFT 1

static int alpha = 2<<V_PARAM_SHIFT;

static int beta  = 4<<V_PARAM_SHIFT;

static int gamma = 1<<V_PARAM_SHIFT;

module_param(alpha, int, 0644);

MODULE_PARM_DESC(alpha, "lower bound of packets in network (scale by 2)");

module_param(beta, int, 0644);

MODULE_PARM_DESC(beta, "upper bound of packets in network (scale by 2)");

module_param(gamma, int, 0644);

MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)");

/* There are several situations when we must "re-start" Vegas:

 *

 *  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)

 *

 * In these circumstances we cannot do a Vegas calculation at the

 * end of the first RTT, because any calculation we do is using

 * stale info -- both the saved cwnd and congestion feedback are

 * stale.

 *

 * Instead we must wait until the completion of an RTT during

 * which we actually receive ACKs.

 */

static void vegas_enable(struct sock *sk)

{

        const struct tcp_sock *tp = tcp_sk(sk);

        struct vegas *vegas = inet_csk_ca(sk);

        /* Begin taking Vegas samples next time we send something. */

        vegas->doing_vegas_now = 1;

        /* Set the beginning of the next send window. */

        vegas->beg_snd_nxt = tp->snd_nxt;

        vegas->cntRTT = 0;

        vegas->minRTT = 0x7fffffff;

}

/* Stop taking Vegas samples for now. */

static inline void vegas_disable(struct sock *sk)

{

        struct vegas *vegas = inet_csk_ca(sk);

        vegas->doing_vegas_now = 0;

}

void tcp_vegas_init(struct sock *sk)

{

        struct vegas *vegas = inet_csk_ca(sk);

        vegas->baseRTT = 0x7fffffff;

        vegas_enable(sk);

}

EXPORT_SYMBOL_GPL(tcp_vegas_init);

/* Do RTT sampling needed for Vegas.

 * Basically we:

 *   o min-filter RTT samples from within an RTT to get the current

 *     propagation delay + queuing delay (we are min-filtering to try to

 *     avoid the effects of delayed ACKs)

 *   o min-filter RTT samples from a much longer window (forever for now)

 *     to find the propagation delay (baseRTT)

 */

void tcp_vegas_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)

{

        struct vegas *vegas = 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 < vegas->baseRTT)

                vegas->baseRTT = vrtt;

        /* Find the min RTT during the last RTT to find

         * the current prop. delay + queuing delay:

         */

        vegas->minRTT = min(vegas->minRTT, vrtt);

        vegas->cntRTT++;

}

EXPORT_SYMBOL_GPL(tcp_vegas_pkts_acked);

void tcp_vegas_state(struct sock *sk, u8 ca_state)

{

        if (ca_state == TCP_CA_Open)

                vegas_enable(sk);

        else

                vegas_disable(sk);

}

EXPORT_SYMBOL_GPL(tcp_vegas_state);

/*

 * If the connection is idle and we are restarting,

 * then we don't want to do any Vegas calculations

 * until we get fresh RTT samples.  So when we

 * restart, we reset our Vegas state to a clean

 * slate. After we get acks for this flight of

 * packets, _then_ we can make Vegas calculations

 * again.

 */

void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event)

{

        if (event == CA_EVENT_CWND_RESTART ||

            event == CA_EVENT_TX_START)

                tcp_vegas_init(sk);

}

EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event);

static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,

                                 u32 in_flight, int flag)

{

        struct tcp_sock *tp = tcp_sk(sk);

        struct vegas *vegas = inet_csk_ca(sk);

        if (!vegas->doing_vegas_now)

                return tcp_reno_cong_avoid(sk, ack, in_flight, flag);

        /* The key players are v_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_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_beg_snd_una) / (rtt duration)

         *

         * Unfortunately, v_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 nicely 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, vegas->beg_snd_nxt)) {

                /* Do the Vegas once-per-RTT cwnd adjustment. */

                u32 old_wnd, old_snd_cwnd;

                /* Here old_wnd is essentially the window of data that was

                 * sent during the previous RTT, and has all

                 * been acknowledged in the course of the RTT that ended

                 * with the ACK we just received. Likewise, old_snd_cwnd

                 * is the cwnd during the previous RTT.

                 */

                old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /

                        tp->mss_cache;

                old_snd_cwnd = vegas->beg_snd_cwnd;

                /* Save the extent of the current window so we can use this

                 * at the end of the next RTT.

                 */

                vegas->beg_snd_una  = vegas->beg_snd_nxt;

                vegas->beg_snd_nxt  = tp->snd_nxt;

                vegas->beg_snd_cwnd = tp->snd_cwnd;

                /* 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 (vegas->cntRTT <= 2) {

                        /* We don't have enough RTT samples to do the Vegas

                         * calculation, so we'll behave like Reno.

                         */

                        tcp_reno_cong_avoid(sk, ack, in_flight, flag);

                } else {

                        u32 rtt, target_cwnd, diff;

                        /* 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 = vegas->minRTT;

                        /* Calculate the cwnd we should have, if we weren't

                         * going too fast.

                         *

                         * This is:

                         *     (actual rate in segments) * baseRTT

                         * We keep it as a fixed point number with

                         * V_PARAM_SHIFT bits to the right of the binary point.

                         */

                        target_cwnd = ((old_wnd * vegas->baseRTT)

                                       << V_PARAM_SHIFT) / rtt;

                        /* Calculate the difference between the window we had,

                         * and the window we would like to have. This quantity

                         * is the "Diff" from the Arizona Vegas papers.

                         *

                         * Again, this is a fixed point number with

                         * V_PARAM_SHIFT bits to the right of the binary

                         * point.

                         */

                        diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;

                        if (diff > gamma && tp->snd_ssthresh > 2 ) {

                                /* Going too fast. Time to slow down

                                 * and switch to congestion avoidance.

                                 */

                                tp->snd_ssthresh = 2;

                                /* Set cwnd to match the actual rate

                                 * exactly:

                                 *   cwnd = (actual rate) * baseRTT

                                 * Then we add 1 because the integer

                                 * truncation robs us of full link

                                 * utilization.

                                 */

                                tp->snd_cwnd = min(tp->snd_cwnd,

                                                   (target_cwnd >>

                                                    V_PARAM_SHIFT)+1);

                        } else if (tp->snd_cwnd <= tp->snd_ssthresh) {

                                /* Slow start.  */

                                tcp_slow_start(tp);

                        } else {

                                /* Congestion avoidance. */

                                u32 next_snd_cwnd;

                                /* Figure out where we would like cwnd

                                 * to be.

                                 */

                                if (diff > beta) {

                                        /* The old window was too fast, so

                                         * we slow down.

                                         */

                                        next_snd_cwnd = old_snd_cwnd - 1;

                                } else if (diff < alpha) {

                                        /* We don't have enough extra packets

                                         * in the network, so speed up.

                                         */

                                        next_snd_cwnd = old_snd_cwnd + 1;

                                } else {

                                        /* Sending just as fast as we

                                         * should be.

                                         */

                                        next_snd_cwnd = old_snd_cwnd;

                                }

                                /* Adjust cwnd upward or downward, toward the

                                 * desired value.

                                 */

                                if (next_snd_cwnd > tp->snd_cwnd)

                                        tp->snd_cwnd++;

                                else if (next_snd_cwnd < tp->snd_cwnd)

                                        tp->snd_cwnd--;

                        }

                        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. */

                vegas->cntRTT = 0;

                vegas->minRTT = 0x7fffffff;

        }

        /* Use normal slow start */

        else if (tp->snd_cwnd <= tp->snd_ssthresh)

                tcp_slow_start(tp);

}

/* Extract info for Tcp socket info provided via netlink. */

void tcp_vegas_get_info(struct sock *sk, u32 ext, struct sk_buff *skb)

{

        const struct vegas *ca = inet_csk_ca(sk);

        if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {

                struct tcpvegas_info info = {

                        .tcpv_enabled = ca->doing_vegas_now,

                        .tcpv_rttcnt = ca->cntRTT,

                        .tcpv_rtt = ca->baseRTT,

                        .tcpv_minrtt = ca->minRTT,

                };

                nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);

        }

}

EXPORT_SYMBOL_GPL(tcp_vegas_get_info);

static struct tcp_congestion_ops tcp_vegas = {

        .flags          = TCP_CONG_RTT_STAMP,

        .init           = tcp_vegas_init,

        .ssthresh       = tcp_reno_ssthresh,

        .cong_avoid     = tcp_vegas_cong_avoid,

        .min_cwnd       = tcp_reno_min_cwnd,

        .pkts_acked     = tcp_vegas_pkts_acked,

        .set_state      = tcp_vegas_state,

        .cwnd_event     = tcp_vegas_cwnd_event,

        .get_info       = tcp_vegas_get_info,

        .owner          = THIS_MODULE,

        .name           = "vegas",

};

static int __init tcp_vegas_register(void)

{

        BUILD_BUG_ON(sizeof(struct vegas) > ICSK_CA_PRIV_SIZE);

        tcp_register_congestion_control(&tcp_vegas);

        return 0;

}

static void __exit tcp_vegas_unregister(void)

{

        tcp_unregister_congestion_control(&tcp_vegas);

}

module_init(tcp_vegas_register);

module_exit(tcp_vegas_unregister);

MODULE_AUTHOR("Stephen Hemminger");

MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("TCP Vegas");