xref: /freebsd/sys/netinet/cc/cc_dctcp.c (revision 855acb84ca45f5aa1df94d1f2dd4b5e3e4c58c0e)

/*-
 * Copyright (c) 2007-2008
 *	Swinburne University of Technology, Melbourne, Australia
 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
 * Copyright (c) 2014 Midori Kato <katoon@sfc.wide.ad.jp>
 * Copyright (c) 2014 The FreeBSD Foundation
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * An implementation of the DCTCP algorithm for FreeBSD, based on
 * "Data Center TCP (DCTCP)" by M. Alizadeh, A. Greenberg, D. A. Maltz,
 * J. Padhye, P. Patel, B. Prabhakar, S. Sengupta, and M. Sridharan.,
 * in ACM Conference on SIGCOMM 2010, New York, USA,
 * Originally released as the contribution of Microsoft Research project.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/systm.h>

#include <net/vnet.h>

#include <netinet/tcp.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>
#include <netinet/cc/cc.h>
#include <netinet/cc/cc_module.h>

#define MAX_ALPHA_VALUE 1024
VNET_DEFINE_STATIC(uint32_t, dctcp_alpha) = 0;
#define V_dctcp_alpha	    VNET(dctcp_alpha)
VNET_DEFINE_STATIC(uint32_t, dctcp_shift_g) = 4;
#define	V_dctcp_shift_g	    VNET(dctcp_shift_g)
VNET_DEFINE_STATIC(uint32_t, dctcp_slowstart) = 0;
#define	V_dctcp_slowstart   VNET(dctcp_slowstart)

struct dctcp {
	int     bytes_ecn;	/* # of marked bytes during a RTT */
	int     bytes_total;	/* # of acked bytes during a RTT */
	int     alpha;		/* the fraction of marked bytes */
	int     ce_prev;	/* CE state of the last segment */
	int     save_sndnxt;	/* end sequence number of the current window */
	int	ece_curr;	/* ECE flag in this segment */
	int	ece_prev;	/* ECE flag in the last segment */
	uint32_t    num_cong_events; /* # of congestion events */
};

static MALLOC_DEFINE(M_dctcp, "dctcp data",
    "Per connection data required for the dctcp algorithm");

static void	dctcp_ack_received(struct cc_var *ccv, uint16_t type);
static void	dctcp_after_idle(struct cc_var *ccv);
static void	dctcp_cb_destroy(struct cc_var *ccv);
static int	dctcp_cb_init(struct cc_var *ccv);
static void	dctcp_cong_signal(struct cc_var *ccv, uint32_t type);
static void	dctcp_conn_init(struct cc_var *ccv);
static void	dctcp_post_recovery(struct cc_var *ccv);
static void	dctcp_ecnpkt_handler(struct cc_var *ccv);
static void	dctcp_update_alpha(struct cc_var *ccv);

struct cc_algo dctcp_cc_algo = {
	.name = "dctcp",
	.ack_received = dctcp_ack_received,
	.cb_destroy = dctcp_cb_destroy,
	.cb_init = dctcp_cb_init,
	.cong_signal = dctcp_cong_signal,
	.conn_init = dctcp_conn_init,
	.post_recovery = dctcp_post_recovery,
	.ecnpkt_handler = dctcp_ecnpkt_handler,
	.after_idle = dctcp_after_idle,
};

static void
dctcp_ack_received(struct cc_var *ccv, uint16_t type)
{
	struct dctcp *dctcp_data;
	int bytes_acked = 0;

	dctcp_data = ccv->cc_data;

	if (CCV(ccv, t_flags) & TF_ECN_PERMIT) {
		/*
		 * DCTCP doesn't treat receipt of ECN marked packet as a
		 * congestion event. Thus, DCTCP always executes the ACK
		 * processing out of congestion recovery.
		 */
		if (IN_CONGRECOVERY(CCV(ccv, t_flags))) {
			EXIT_CONGRECOVERY(CCV(ccv, t_flags));
			newreno_cc_algo.ack_received(ccv, type);
			ENTER_CONGRECOVERY(CCV(ccv, t_flags));
		} else
			newreno_cc_algo.ack_received(ccv, type);

		if (type == CC_DUPACK)
			bytes_acked = CCV(ccv, t_maxseg);

		if (type == CC_ACK)
			bytes_acked = ccv->bytes_this_ack;

		/* Update total bytes. */
		dctcp_data->bytes_total += bytes_acked;

		/* Update total marked bytes. */
		if (dctcp_data->ece_curr) {
			if (!dctcp_data->ece_prev
			    && bytes_acked > CCV(ccv, t_maxseg)) {
				dctcp_data->bytes_ecn +=
				    (bytes_acked - CCV(ccv, t_maxseg));
			} else
				dctcp_data->bytes_ecn += bytes_acked;
			dctcp_data->ece_prev = 1;
		} else {
			if (dctcp_data->ece_prev
			    && bytes_acked > CCV(ccv, t_maxseg))
				dctcp_data->bytes_ecn += CCV(ccv, t_maxseg);
			dctcp_data->ece_prev = 0;
		}
		dctcp_data->ece_curr = 0;

		/*
		 * Update the fraction of marked bytes at the end of
		 * current window size.
		 */
		if ((IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
		    SEQ_GEQ(ccv->curack, CCV(ccv, snd_recover))) ||
		    (!IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
		    SEQ_GT(ccv->curack, dctcp_data->save_sndnxt)))
			dctcp_update_alpha(ccv);
	} else
		newreno_cc_algo.ack_received(ccv, type);
}

static void
dctcp_after_idle(struct cc_var *ccv)
{
	struct dctcp *dctcp_data;

	dctcp_data = ccv->cc_data;

	/* Initialize internal parameters after idle time */
	dctcp_data->bytes_ecn = 0;
	dctcp_data->bytes_total = 0;
	dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
	dctcp_data->alpha = V_dctcp_alpha;
	dctcp_data->ece_curr = 0;
	dctcp_data->ece_prev = 0;
	dctcp_data->num_cong_events = 0;

	dctcp_cc_algo.after_idle = newreno_cc_algo.after_idle;
}

static void
dctcp_cb_destroy(struct cc_var *ccv)
{
	free(ccv->cc_data, M_dctcp);
}

static int
dctcp_cb_init(struct cc_var *ccv)
{
	struct dctcp *dctcp_data;

	dctcp_data = malloc(sizeof(struct dctcp), M_dctcp, M_NOWAIT|M_ZERO);

	if (dctcp_data == NULL)
		return (ENOMEM);

	/* Initialize some key variables with sensible defaults. */
	dctcp_data->bytes_ecn = 0;
	dctcp_data->bytes_total = 0;
	/*
	 * When alpha is set to 0 in the beginning, DCTCP sender transfers as
	 * much data as possible until the value converges which may expand the
	 * queueing delay at the switch. When alpha is set to 1, queueing delay
	 * is kept small.
	 * Throughput-sensitive applications should have alpha = 0
	 * Latency-sensitive applications should have alpha = 1
	 *
	 * Note: DCTCP draft suggests initial alpha to be 1 but we've decided to
	 * keep it 0 as default.
	 */
	dctcp_data->alpha = V_dctcp_alpha;
	dctcp_data->save_sndnxt = 0;
	dctcp_data->ce_prev = 0;
	dctcp_data->ece_curr = 0;
	dctcp_data->ece_prev = 0;
	dctcp_data->num_cong_events = 0;

	ccv->cc_data = dctcp_data;
	return (0);
}

/*
 * Perform any necessary tasks before we enter congestion recovery.
 */
static void
dctcp_cong_signal(struct cc_var *ccv, uint32_t type)
{
	struct dctcp *dctcp_data;
	u_int win, mss;

	dctcp_data = ccv->cc_data;
	win = CCV(ccv, snd_cwnd);
	mss = CCV(ccv, t_maxseg);

	switch (type) {
	case CC_NDUPACK:
		if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
			if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
				CCV(ccv, snd_ssthresh) = mss *
				    max(win / 2 / mss, 2);
				dctcp_data->num_cong_events++;
			} else {
				/* cwnd has already updated as congestion
				 * recovery. Reverse cwnd value using
				 * snd_cwnd_prev and recalculate snd_ssthresh
				 */
				win = CCV(ccv, snd_cwnd_prev);
				CCV(ccv, snd_ssthresh) =
				    max(win / 2 / mss, 2) * mss;
			}
			ENTER_RECOVERY(CCV(ccv, t_flags));
		}
		break;
	case CC_ECN:
		/*
		 * Save current snd_cwnd when the host encounters both
		 * congestion recovery and fast recovery.
		 */
		CCV(ccv, snd_cwnd_prev) = win;
		if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
			if (V_dctcp_slowstart &&
			    dctcp_data->num_cong_events++ == 0) {
				CCV(ccv, snd_ssthresh) =
				    mss * max(win / 2 / mss, 2);
				dctcp_data->alpha = MAX_ALPHA_VALUE;
				dctcp_data->bytes_ecn = 0;
				dctcp_data->bytes_total = 0;
				dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
			} else
				CCV(ccv, snd_ssthresh) = max((win - ((win *
				    dctcp_data->alpha) >> 11)) / mss, 2) * mss;
			CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
			ENTER_CONGRECOVERY(CCV(ccv, t_flags));
		}
		dctcp_data->ece_curr = 1;
		break;
	case CC_RTO:
		if (CCV(ccv, t_flags) & TF_ECN_PERMIT) {
			CCV(ccv, t_flags) |= TF_ECN_SND_CWR;
			dctcp_update_alpha(ccv);
			dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
			dctcp_data->num_cong_events++;
		}
		break;
	}
}

static void
dctcp_conn_init(struct cc_var *ccv)
{
	struct dctcp *dctcp_data;

	dctcp_data = ccv->cc_data;

	if (CCV(ccv, t_flags) & TF_ECN_PERMIT)
		dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
}

/*
 * Perform any necessary tasks before we exit congestion recovery.
 */
static void
dctcp_post_recovery(struct cc_var *ccv)
{
	dctcp_cc_algo.post_recovery = newreno_cc_algo.post_recovery;

	if (CCV(ccv, t_flags) & TF_ECN_PERMIT)
		dctcp_update_alpha(ccv);
}

/*
 * Execute an additional ECN processing using ECN field in IP header and the CWR
 * bit in TCP header.
 *
 * delay_ack == 0 - Delayed ACK disabled
 * delay_ack == 1 - Delayed ACK enabled
 */

static void
dctcp_ecnpkt_handler(struct cc_var *ccv)
{
	struct dctcp *dctcp_data;
	uint32_t ccflag;
	int delay_ack;

	dctcp_data = ccv->cc_data;
	ccflag = ccv->flags;
	delay_ack = 1;

	/*
	 * DCTCP responses an ACK immediately when the CE state
	 * in between this segment and the last segment is not same.
	 */
	if (ccflag & CCF_IPHDR_CE) {
		if (!dctcp_data->ce_prev && (ccflag & CCF_DELACK))
			delay_ack = 0;
		dctcp_data->ce_prev = 1;
		CCV(ccv, t_flags) |= TF_ECN_SND_ECE;
	} else {
		if (dctcp_data->ce_prev && (ccflag & CCF_DELACK))
			delay_ack = 0;
		dctcp_data->ce_prev = 0;
		CCV(ccv, t_flags) &= ~TF_ECN_SND_ECE;
	}

	/* DCTCP sets delayed ack when this segment sets the CWR flag. */
	if ((ccflag & CCF_DELACK) && (ccflag & CCF_TCPHDR_CWR))
		delay_ack = 1;

	if (delay_ack == 0)
		ccv->flags |= CCF_ACKNOW;
	else
		ccv->flags &= ~CCF_ACKNOW;
}

/*
 * Update the fraction of marked bytes represented as 'alpha'.
 * Also initialize several internal parameters at the end of this function.
 */
static void
dctcp_update_alpha(struct cc_var *ccv)
{
	struct dctcp *dctcp_data;
	int alpha_prev;

	dctcp_data = ccv->cc_data;
	alpha_prev = dctcp_data->alpha;
	dctcp_data->bytes_total = max(dctcp_data->bytes_total, 1);

	/*
	 * Update alpha: alpha = (1 - g) * alpha + g * F.
	 * Here:
	 * g is weight factor
	 *	recommaded to be set to 1/16
	 *	small g = slow convergence between competitive DCTCP flows
	 *	large g = impacts low utilization of bandwidth at switches
	 * F is fraction of marked segments in last RTT
	 *	updated every RTT
	 * Alpha must be round to 0 - MAX_ALPHA_VALUE.
	 */
	dctcp_data->alpha = min(alpha_prev - (alpha_prev >> V_dctcp_shift_g) +
	    (dctcp_data->bytes_ecn << (10 - V_dctcp_shift_g)) /
	    dctcp_data->bytes_total, MAX_ALPHA_VALUE);

	/* Initialize internal parameters for next alpha calculation */
	dctcp_data->bytes_ecn = 0;
	dctcp_data->bytes_total = 0;
	dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
}

static int
dctcp_alpha_handler(SYSCTL_HANDLER_ARGS)
{
	uint32_t new;
	int error;

	new = V_dctcp_alpha;
	error = sysctl_handle_int(oidp, &new, 0, req);
	if (error == 0 && req->newptr != NULL) {
		if (new > 1)
			error = EINVAL;
		else {
			if (new > MAX_ALPHA_VALUE)
				V_dctcp_alpha = MAX_ALPHA_VALUE;
			else
				V_dctcp_alpha = new;
		}
	}

	return (error);
}

static int
dctcp_shift_g_handler(SYSCTL_HANDLER_ARGS)
{
	uint32_t new;
	int error;

	new = V_dctcp_shift_g;
	error = sysctl_handle_int(oidp, &new, 0, req);
	if (error == 0 && req->newptr != NULL) {
		if (new > 1)
			error = EINVAL;
		else
			V_dctcp_shift_g = new;
	}

	return (error);
}

static int
dctcp_slowstart_handler(SYSCTL_HANDLER_ARGS)
{
	uint32_t new;
	int error;

	new = V_dctcp_slowstart;
	error = sysctl_handle_int(oidp, &new, 0, req);
	if (error == 0 && req->newptr != NULL) {
		if (new > 1)
			error = EINVAL;
		else
			V_dctcp_slowstart = new;
	}

	return (error);
}

SYSCTL_DECL(_net_inet_tcp_cc_dctcp);
SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, dctcp, CTLFLAG_RW, NULL,
    "dctcp congestion control related settings");

SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, alpha,
    CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_alpha), 0,
    &dctcp_alpha_handler,
    "IU", "dctcp alpha parameter");

SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, shift_g,
    CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_shift_g), 4,
    &dctcp_shift_g_handler,
    "IU", "dctcp shift parameter");

SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, slowstart,
    CTLFLAG_VNET|CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(dctcp_slowstart), 0,
    &dctcp_slowstart_handler,
    "IU", "half CWND reduction after the first slow start");

DECLARE_CC_MODULE(dctcp, &dctcp_cc_algo);