Commit a7868ea6 authored by Baruch Even's avatar Baruch Even Committed by David S. Miller
Browse files

[TCP]: Add H-TCP congestion control module. 



H-TCP is a congestion control algorithm developed at the Hamilton Institute, by
Douglas Leith and Robert Shorten. It is extending the standard Reno algorithm
with mode switching is thus a relatively simple modification.

H-TCP is defined in a layered manner as it is still a research platform. The
basic form includes the modification of beta according to the ratio of maxRTT
to min RTT and the alpha=2*factor*(1-beta) relation, where factor is dependant
on the time since last congestion.

The other layers improve convergence by adding appropriate factors to alpha.

The following patch implements the H-TCP algorithm in it's basic form.

Signed-Off-By: default avatarBaruch Even <baruch@ev-en.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b87d8561

net/ipv4/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -467,6 +467,18 @@ config TCP_CONG_WESTWOOD 
	TCP Westwood+ significantly increases fairness wrt TCP Reno in

	wired networks and throughput over wireless links.



config TCP_CONG_HTCP

        tristate "H-TCP"

	depends on INET

        default m

	---help---

	H-TCP is a send-side only modifications of the TCP Reno

	protocol stack that optimizes the performance of TCP

	congestion control for high speed network links. It uses a

	modeswitch to change the alpha and beta parameters of TCP Reno

	based on network conditions and in a way so as to be fair with

	other Reno and H-TCP flows.



config TCP_CONG_HSTCP

	tristate "High Speed TCP"

	depends on INET && EXPERIMENTAL
@@ -499,6 +511,7 @@ config TCP_CONG_VEGAS 
	window. TCP Vegas should provide less packet loss, but it is

	not as aggressive as TCP Reno.





endmenu



source "net/ipv4/ipvs/Kconfig"

net/ipv4/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -35,6 +35,7 @@ obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o 
obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o

obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o

obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o

obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o

obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o



obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \

net/ipv4/tcp_htcp.c

0 → 100644
+289 −0
Original line number Diff line number Diff line 
/*

 * H-TCP congestion control. The algorithm is detailed in:

 * R.N.Shorten, D.J.Leith:

 *   "H-TCP: TCP for high-speed and long-distance networks"

 *   Proc. PFLDnet, Argonne, 2004.

 * http://www.hamilton.ie/net/htcp3.pdf

 */



#include <linux/config.h>

#include <linux/mm.h>

#include <linux/module.h>

#include <net/tcp.h>



#define ALPHA_BASE	(1<<7)  /* 1.0 with shift << 7 */

#define BETA_MIN	(1<<6)  /* 0.5 with shift << 7 */

#define BETA_MAX	102	/* 0.8 with shift << 7 */



static int use_rtt_scaling = 1;

module_param(use_rtt_scaling, int, 0644);

MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");



static int use_bandwidth_switch = 1;

module_param(use_bandwidth_switch, int, 0644);

MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");



struct htcp {

	u16	alpha;		/* Fixed point arith, << 7 */

	u8	beta;           /* Fixed point arith, << 7 */

	u8	modeswitch;     /* Delay modeswitch until we had at least one congestion event */

	u8	ccount;		/* Number of RTTs since last congestion event */

	u8	undo_ccount;

	u16	packetcount;

	u32	minRTT;

	u32	maxRTT;

	u32	snd_cwnd_cnt2;



	u32	undo_maxRTT;

	u32	undo_old_maxB;



	/* Bandwidth estimation */

	u32	minB;

	u32	maxB;

	u32	old_maxB;

	u32	Bi;

	u32	lasttime;

};



static inline void htcp_reset(struct htcp *ca)

{

	ca->undo_ccount = ca->ccount;

	ca->undo_maxRTT = ca->maxRTT;

	ca->undo_old_maxB = ca->old_maxB;



	ca->ccount = 0;

	ca->snd_cwnd_cnt2 = 0;

}



static u32 htcp_cwnd_undo(struct tcp_sock *tp)

{

	struct htcp *ca = tcp_ca(tp);

	ca->ccount = ca->undo_ccount;

	ca->maxRTT = ca->undo_maxRTT;

	ca->old_maxB = ca->undo_old_maxB;

	return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);

}



static inline void measure_rtt(struct tcp_sock *tp)

{

	struct htcp *ca = tcp_ca(tp);

	u32 srtt = tp->srtt>>3;



	/* keep track of minimum RTT seen so far, minRTT is zero at first */

	if (ca->minRTT > srtt || !ca->minRTT)

		ca->minRTT = srtt;



	/* max RTT */

	if (tp->ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && ca->ccount > 3) {

		if (ca->maxRTT < ca->minRTT)

			ca->maxRTT = ca->minRTT;

		if (ca->maxRTT < srtt && srtt <= ca->maxRTT+HZ/50)

			ca->maxRTT = srtt;

	}

}



static void measure_achieved_throughput(struct tcp_sock *tp, u32 pkts_acked)

{

	struct htcp *ca = tcp_ca(tp);

	u32 now = tcp_time_stamp;



	/* achieved throughput calculations */

	if (tp->ca_state != TCP_CA_Open && tp->ca_state != TCP_CA_Disorder) {

		ca->packetcount = 0;

		ca->lasttime = now;

		return;

	}



	ca->packetcount += pkts_acked;



	if (ca->packetcount >= tp->snd_cwnd - (ca->alpha>>7? : 1)

			&& now - ca->lasttime >= ca->minRTT

			&& ca->minRTT > 0) {

		__u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);

		if (ca->ccount <= 3) {

			/* just after backoff */

			ca->minB = ca->maxB = ca->Bi = cur_Bi;

		} else {

			ca->Bi = (3*ca->Bi + cur_Bi)/4;

			if (ca->Bi > ca->maxB)

				ca->maxB = ca->Bi;

			if (ca->minB > ca->maxB)

				ca->minB = ca->maxB;

		}

		ca->packetcount = 0;

		ca->lasttime = now;

	}

}



static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)

{

	if (use_bandwidth_switch) {

		u32 maxB = ca->maxB;

		u32 old_maxB = ca->old_maxB;

		ca->old_maxB = ca->maxB;



		if (!between(5*maxB, 4*old_maxB, 6*old_maxB)) {

			ca->beta = BETA_MIN;

			ca->modeswitch = 0;

			return;

		}

	}



	if (ca->modeswitch && minRTT > max(HZ/100, 1) && maxRTT) {

		ca->beta = (minRTT<<7)/maxRTT;

		if (ca->beta < BETA_MIN)

			ca->beta = BETA_MIN;

		else if (ca->beta > BETA_MAX)

			ca->beta = BETA_MAX;

	} else {

		ca->beta = BETA_MIN;

		ca->modeswitch = 1;

	}

}



static inline void htcp_alpha_update(struct htcp *ca)

{

	u32 minRTT = ca->minRTT;

	u32 factor = 1;

	u32 diff = ca->ccount * minRTT; /* time since last backoff */



	if (diff > HZ) {

		diff -= HZ;

		factor = 1+ ( 10*diff + ((diff/2)*(diff/2)/HZ) )/HZ;

	}



	if (use_rtt_scaling && minRTT) {

		u32 scale = (HZ<<3)/(10*minRTT);

		scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to interval [0.5,10]<<3 */

		factor = (factor<<3)/scale;

		if (!factor)

			factor = 1;

	}



	ca->alpha = 2*factor*((1<<7)-ca->beta);

	if (!ca->alpha)

		ca->alpha = ALPHA_BASE;

}



/* After we have the rtt data to calculate beta, we'd still prefer to wait one

 * rtt before we adjust our beta to ensure we are working from a consistent

 * data.

 *

 * This function should be called when we hit a congestion event since only at

 * that point do we really have a real sense of maxRTT (the queues en route

 * were getting just too full now).

 */

static void htcp_param_update(struct tcp_sock *tp)

{

	struct htcp *ca = tcp_ca(tp);

	u32 minRTT = ca->minRTT;

	u32 maxRTT = ca->maxRTT;



	htcp_beta_update(ca, minRTT, maxRTT);

	htcp_alpha_update(ca);



	/* add slowly fading memory for maxRTT to accommodate routing changes etc */

	if (minRTT > 0 && maxRTT > minRTT)

		ca->maxRTT = minRTT + ((maxRTT-minRTT)*95)/100;

}



static u32 htcp_recalc_ssthresh(struct tcp_sock *tp)

{

	struct htcp *ca = tcp_ca(tp);

	htcp_param_update(tp);

	return max((tp->snd_cwnd * ca->beta) >> 7, 2U);

}



static void htcp_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,

			    u32 in_flight, int data_acked)

{

	struct htcp *ca = tcp_ca(tp);



	if (in_flight < tp->snd_cwnd)

		return;



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

                /* In "safe" area, increase. */

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

			tp->snd_cwnd++;

	} else {

		measure_rtt(tp);



		/* keep track of number of round-trip times since last backoff event */

		if (ca->snd_cwnd_cnt2++ > tp->snd_cwnd) {

			ca->ccount++;

			ca->snd_cwnd_cnt2 = 0;

			htcp_alpha_update(ca);

		}



                /* In dangerous area, increase slowly.

		 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd

		 */

		if ((tp->snd_cwnd_cnt++ * ca->alpha)>>7 >= tp->snd_cwnd) {

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

				tp->snd_cwnd++;

			tp->snd_cwnd_cnt = 0;

			ca->ccount++;

		}

	}

}



/* Lower bound on congestion window. */

static u32 htcp_min_cwnd(struct tcp_sock *tp)

{

	return tp->snd_ssthresh;

}





static void htcp_init(struct tcp_sock *tp)

{

	struct htcp *ca = tcp_ca(tp);



	memset(ca, 0, sizeof(struct htcp));

	ca->alpha = ALPHA_BASE;

	ca->beta = BETA_MIN;

}



static void htcp_state(struct tcp_sock *tp, u8 new_state)

{

	switch (new_state) {

	case TCP_CA_CWR:

	case TCP_CA_Recovery:

	case TCP_CA_Loss:

		htcp_reset(tcp_ca(tp));

		break;

	}

}



static struct tcp_congestion_ops htcp = {

	.init		= htcp_init,

	.ssthresh	= htcp_recalc_ssthresh,

	.min_cwnd	= htcp_min_cwnd,

	.cong_avoid	= htcp_cong_avoid,

	.set_state	= htcp_state,

	.undo_cwnd	= htcp_cwnd_undo,

	.pkts_acked	= measure_achieved_throughput,

	.owner		= THIS_MODULE,

	.name		= "htcp",

};



static int __init htcp_register(void)

{

	BUG_ON(sizeof(struct htcp) > TCP_CA_PRIV_SIZE);

	BUILD_BUG_ON(BETA_MIN >= BETA_MAX);

	if (!use_bandwidth_switch)

		htcp.pkts_acked = NULL;

	return tcp_register_congestion_control(&htcp);

}



static void __exit htcp_unregister(void)

{

	tcp_unregister_congestion_control(&htcp);

}



module_init(htcp_register);

module_exit(htcp_unregister);



MODULE_AUTHOR("Baruch Even");

MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("H-TCP");

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