Import an implementation of the CAIA-Hamilton-Delay (CHD) congestion control

algorithm described in the paper "Improved coexistence and loss tolerance for
delay based TCP congestion control" by Hayes and Armitage. It is implemented as
a kernel module compatible with the recently committed modular congestion
control framework.

CHD enhances the approach taken by the Hamilton-Delay (HD) algorithm to provide
tolerance to non-congestion related packet loss and improvements to coexistence
with loss-based congestion control algorithms. A key idea in improving
coexistence with loss-based congestion control algorithms is the use of a shadow
window, which attempts to track how NewReno's congestion window (cwnd) would
evolve. At the next packet loss congestion event, CHD uses the shadow window to
correct cwnd in a way that reduces the amount of unfairness CHD experiences when
competing with loss-based algorithms.

In collaboration with:	David Hayes <dahayes at swin edu au> and
				Grenville Armitage <garmitage at swin edu au>
Sponsored by:	FreeBSD Foundation
Reviewed by:	bz and others along the way
MFC after:	3 months

3 files changed, 508 insertions, 1 deletions

diff --git a/sys/modules/cc/Makefile b/sys/modules/cc/Makefile
index f03c147..e3e8336 100644
--- a/sys/modules/cc/Makefile
+++ b/sys/modules/cc/Makefile
@@ -1,6 +1,7 @@
 # $FreeBSD$
 
-SUBDIR=	cc_cubic \
+SUBDIR=	cc_chd \
+	cc_cubic \
 	cc_hd \
 	cc_htcp \
 	cc_vegas
diff --git a/sys/modules/cc/cc_chd/Makefile b/sys/modules/cc/cc_chd/Makefile
new file mode 100644
index 0000000..20577f8
--- /dev/null
+++ b/sys/modules/cc/cc_chd/Makefile
@@ -0,0 +1,9 @@
+# $FreeBSD$
+
+.include <bsd.own.mk>
+
+.PATH: ${.CURDIR}/../../../netinet/cc
+KMOD=	cc_chd
+SRCS=	cc_chd.c
+
+.include <bsd.kmod.mk>
diff --git a/sys/netinet/cc/cc_chd.c b/sys/netinet/cc/cc_chd.c
new file mode 100644
index 0000000..4b1d2c4
--- /dev/null
+++ b/sys/netinet/cc/cc_chd.c
@@ -0,0 +1,497 @@
+/*-
+ * Copyright (c) 2009-2010
+ *	Swinburne University of Technology, Melbourne, Australia
+ * Copyright (c) 2010-2011 The FreeBSD Foundation
+ * All rights reserved.
+ *
+ * This software was developed at the Centre for Advanced Internet
+ * Architectures, Swinburne University, by David Hayes and Lawrence Stewart,
+ * made possible in part by a grant from the Cisco University Research Program
+ * Fund at Community Foundation Silicon Valley.
+ *
+ * Portions of this software were developed at the Centre for Advanced Internet
+ * Architectures, Swinburne University of Technology, Melbourne, Australia by
+ * David Hayes under sponsorship from the FreeBSD Foundation.
+ *
+ * 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 CAIA-Hamilton delay based congestion control
+ * algorithm, based on "Improved coexistence and loss tolerance for delay based
+ * TCP congestion control" by D. A. Hayes and G. Armitage., in 35th Annual IEEE
+ * Conference on Local Computer Networks (LCN 2010), Denver, Colorado, USA,
+ * 11-14 October 2010.
+ *
+ * Originally released as part of the NewTCP research project at Swinburne
+ * University's Centre for Advanced Internet Architectures, Melbourne,
+ * Australia, which was made possible in part by a grant from the Cisco
+ * University Research Program Fund at Community Foundation Silicon Valley. More
+ * details are available at:
+ *   http://caia.swin.edu.au/urp/newtcp/
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/khelp.h>
+#include <sys/limits.h>
+#include <sys/malloc.h>
+#include <sys/module.h>
+#include <sys/queue.h>
+#include <sys/socket.h>
+#include <sys/socketvar.h>
+#include <sys/sysctl.h>
+#include <sys/systm.h>
+
+#include <net/if.h>
+#include <net/vnet.h>
+
+#include <netinet/cc.h>
+#include <netinet/tcp_seq.h>
+#include <netinet/tcp_timer.h>
+#include <netinet/tcp_var.h>
+
+#include <netinet/cc/cc_module.h>
+
+#include <netinet/khelp/h_ertt.h>
+
+#define	CAST_PTR_INT(X)	(*((int*)(X)))
+
+/*
+ * Private signal type for rate based congestion signal.
+ * See <netinet/cc.h> for appropriate bit-range to use for private signals.
+ */
+#define	CC_CHD_DELAY	0x02000000
+
+/* Largest possible number returned by random(). */
+#define	RANDOM_MAX	INT_MAX
+
+static void	chd_ack_received(struct cc_var *ccv, uint16_t ack_type);
+static void	chd_cb_destroy(struct cc_var *ccv);
+static int	chd_cb_init(struct cc_var *ccv);
+static void	chd_cong_signal(struct cc_var *ccv, uint32_t signal_type);
+static void	chd_conn_init(struct cc_var *ccv);
+static int	chd_mod_init(void);
+
+struct chd {
+	/*
+	 * Shadow window - keeps track of what the NewReno congestion window
+	 * would have been if delay-based cwnd backoffs had not been made. This
+	 * functionality aids coexistence with loss-based TCP flows which may be
+	 * sharing links along the path.
+	 */
+	unsigned long shadow_w;
+	/*
+	 * Loss-based TCP compatibility flag - When set, it turns on the shadow
+	 * window functionality.
+	 */
+	int loss_compete;
+	 /* The maximum round trip time seen within a measured rtt period. */
+	int maxrtt_in_rtt;
+	/* The previous qdly that caused cwnd to backoff. */
+	int prev_backoff_qdly;
+};
+
+static int ertt_id;
+
+static VNET_DEFINE(uint32_t, chd_qmin) = 5;
+static VNET_DEFINE(uint32_t, chd_pmax) = 50;
+static VNET_DEFINE(uint32_t, chd_loss_fair) = 1;
+static VNET_DEFINE(uint32_t, chd_use_max) = 1;
+static VNET_DEFINE(uint32_t, chd_qthresh) = 20;
+#define	V_chd_qthresh	VNET(chd_qthresh)
+#define	V_chd_qmin	VNET(chd_qmin)
+#define	V_chd_pmax	VNET(chd_pmax)
+#define	V_chd_loss_fair	VNET(chd_loss_fair)
+#define	V_chd_use_max	VNET(chd_use_max)
+
+MALLOC_DECLARE(M_CHD);
+MALLOC_DEFINE(M_CHD, "chd data",
+    "Per connection data required for the CHD congestion control algorithm");
+
+struct cc_algo chd_cc_algo = {
+	.name = "chd",
+	.ack_received = chd_ack_received,
+	.cb_destroy = chd_cb_destroy,
+	.cb_init = chd_cb_init,
+	.cong_signal = chd_cong_signal,
+	.conn_init = chd_conn_init,
+	.mod_init = chd_mod_init
+};
+
+static __inline void
+chd_window_decrease(struct cc_var *ccv)
+{
+	unsigned long win;
+
+	win = min(CCV(ccv, snd_wnd), CCV(ccv, snd_cwnd)) / CCV(ccv, t_maxseg);
+	win -= max((win / 2), 1);
+	CCV(ccv, snd_ssthresh) = max(win, 2) * CCV(ccv, t_maxseg);
+}
+
+/*
+ * Probabilistic backoff function. Returns 1 if we should backoff or 0
+ * otherwise. The calculation of p is similar to the calculation of p in cc_hd.
+ */
+static __inline int
+should_backoff(int qdly, int maxqdly, struct chd *chd_data)
+{
+	unsigned long p, rand;
+
+	rand = random();
+
+	if (qdly < V_chd_qthresh) {
+		chd_data->loss_compete = 0;
+		p = (((RANDOM_MAX / 100) * V_chd_pmax) /
+		    (V_chd_qthresh - V_chd_qmin)) *
+		    (qdly - V_chd_qmin);
+	} else {
+		if (qdly > V_chd_qthresh) {
+			p = (((RANDOM_MAX / 100) * V_chd_pmax) /
+			    (maxqdly - V_chd_qthresh)) *
+			    (maxqdly - qdly);
+			if (V_chd_loss_fair && rand < p)
+				chd_data->loss_compete = 1;
+		} else {
+			p = (RANDOM_MAX / 100) * V_chd_pmax;
+			chd_data->loss_compete = 0;
+		}
+	}
+
+	return (rand < p);
+}
+
+static __inline void
+chd_window_increase(struct cc_var *ccv, int new_measurement)
+{
+	struct chd *chd_data;
+	int incr;
+
+	chd_data = ccv->cc_data;
+	incr = 0;
+
+	if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh)) {
+		/* Adapted from NewReno slow start. */
+		if (V_tcp_do_rfc3465) {
+			/* In slow-start with ABC enabled. */
+			if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max)) {
+				/* Not due to RTO. */
+				incr = min(ccv->bytes_this_ack,
+				    V_tcp_abc_l_var * CCV(ccv, t_maxseg));
+			} else {
+				/* Due to RTO. */
+				incr = min(ccv->bytes_this_ack,
+				    CCV(ccv, t_maxseg));
+			}
+		} else
+			incr = CCV(ccv, t_maxseg);
+
+	} else { /* Congestion avoidance. */
+		if (V_tcp_do_rfc3465) {
+			if (ccv->flags & CCF_ABC_SENTAWND) {
+				ccv->flags &= ~CCF_ABC_SENTAWND;
+				incr = CCV(ccv, t_maxseg);
+			}
+		} else if (new_measurement)
+			incr = CCV(ccv, t_maxseg);
+	}
+
+	if (chd_data->shadow_w > 0) {
+		/* Track NewReno window. */
+		chd_data->shadow_w = min(chd_data->shadow_w + incr,
+		    TCP_MAXWIN << CCV(ccv, snd_scale));
+	}
+
+	CCV(ccv,snd_cwnd) = min(CCV(ccv, snd_cwnd) + incr,
+	    TCP_MAXWIN << CCV(ccv, snd_scale));
+}
+
+/*
+ * All ACK signals are used for timing measurements to determine delay-based
+ * congestion. However, window increases are only performed when
+ * ack_type == CC_ACK.
+ */
+static void
+chd_ack_received(struct cc_var *ccv, uint16_t ack_type)
+{
+	struct chd *chd_data;
+	struct ertt *e_t;
+	int backoff, new_measurement, qdly, rtt;
+
+	e_t = khelp_get_osd(CCV(ccv, osd), ertt_id);
+	chd_data = ccv->cc_data;
+	new_measurement = e_t->flags & ERTT_NEW_MEASUREMENT;
+	backoff = qdly = 0;
+
+	chd_data->maxrtt_in_rtt = imax(e_t->rtt, chd_data->maxrtt_in_rtt);
+
+	if (new_measurement) {
+		/*
+		 * There is a new per RTT measurement, so check to see if there
+		 * is delay based congestion.
+		 */
+		rtt = V_chd_use_max ? chd_data->maxrtt_in_rtt : e_t->rtt;
+		chd_data->maxrtt_in_rtt = 0;
+
+		if (rtt && e_t->minrtt && !IN_RECOVERY(CCV(ccv, t_flags))) {
+			qdly = rtt - e_t->minrtt;
+			if (qdly > V_chd_qmin) {
+				/*
+				 * Probabilistic delay based congestion
+				 * indication.
+				 */
+				backoff = should_backoff(qdly,
+				    e_t->maxrtt - e_t->minrtt, chd_data);
+			} else
+				chd_data->loss_compete = 0;
+		}
+		/* Reset per RTT measurement flag to start a new measurement. */
+		e_t->flags &= ~ERTT_NEW_MEASUREMENT;
+	}
+
+	if (backoff) {
+		/*
+		 * Update shadow_w before delay based backoff.
+		 */
+		if (chd_data->loss_compete ||
+		    qdly > chd_data->prev_backoff_qdly) {
+			/*
+			 * Delay is higher than when we backed off previously,
+			 * so it is possible that this flow is competing with
+			 * loss based flows.
+			 */
+			chd_data->shadow_w = max(CCV(ccv, snd_cwnd),
+			    chd_data->shadow_w);
+		} else {
+			/*
+			 * Reset shadow_w, as it is probable that this flow is
+			 * not competing with loss based flows at the moment.
+			 */
+			chd_data->shadow_w = 0;
+		}
+
+		chd_data->prev_backoff_qdly = qdly;
+		/*
+		 * Send delay-based congestion signal to the congestion signal
+		 * handler.
+		 */
+		chd_cong_signal(ccv, CC_CHD_DELAY);
+
+	} else if (ack_type == CC_ACK)
+		chd_window_increase(ccv, new_measurement);
+}
+
+static void
+chd_cb_destroy(struct cc_var *ccv)
+{
+
+	if (ccv->cc_data != NULL)
+		free(ccv->cc_data, M_CHD);
+}
+
+static int
+chd_cb_init(struct cc_var *ccv)
+{
+	struct chd *chd_data;
+
+	chd_data = malloc(sizeof(struct chd), M_CHD, M_NOWAIT);
+	if (chd_data == NULL)
+		return (ENOMEM);
+
+	chd_data->shadow_w = 0;
+	ccv->cc_data = chd_data;
+
+	return (0);
+}
+
+static void
+chd_cong_signal(struct cc_var *ccv, uint32_t signal_type)
+{
+	struct ertt *e_t;
+	struct chd *chd_data;
+	int qdly;
+
+	e_t = khelp_get_osd(CCV(ccv, osd), ertt_id);
+	chd_data = ccv->cc_data;
+	qdly = imax(e_t->rtt, chd_data->maxrtt_in_rtt) - e_t->minrtt;
+
+	switch(signal_type) {
+	case CC_CHD_DELAY:
+		chd_window_decrease(ccv); /* Set new ssthresh. */
+		CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
+		CCV(ccv, snd_recover) = CCV(ccv, snd_max);
+		ENTER_CONGRECOVERY(CCV(ccv, t_flags));
+		break;
+
+	case CC_NDUPACK: /* Packet loss. */
+		/*
+		 * Only react to loss as a congestion signal if qdly >
+		 * V_chd_qthresh.  If qdly is less than qthresh, presume that
+		 * this is a non congestion related loss. If qdly is greater
+		 * than qthresh, assume that we are competing with loss based
+		 * tcp flows and restore window from any unnecessary backoffs,
+		 * before the decrease.
+		 */
+		if (!IN_RECOVERY(CCV(ccv, t_flags)) && qdly > V_chd_qthresh) {
+			if (chd_data->loss_compete) {
+				CCV(ccv, snd_cwnd) = max(CCV(ccv, snd_cwnd),
+				    chd_data->shadow_w);
+			}
+			chd_window_decrease(ccv);
+		} else {
+			 /*
+			  * This loss isn't congestion related, or already
+			  * recovering from congestion.
+			  */
+			CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
+			CCV(ccv, snd_recover) = CCV(ccv, snd_max);
+		}
+
+		if (chd_data->shadow_w > 0) {
+			chd_data->shadow_w = max(chd_data->shadow_w /
+			    CCV(ccv, t_maxseg) / 2, 2) * CCV(ccv, t_maxseg);
+		}
+		ENTER_FASTRECOVERY(CCV(ccv, t_flags));
+		break;
+
+	default:
+		newreno_cc_algo.cong_signal(ccv, signal_type);
+	}
+}
+
+static void
+chd_conn_init(struct cc_var *ccv)
+{
+	struct chd *chd_data;
+
+	chd_data = ccv->cc_data;
+	chd_data->prev_backoff_qdly = 0;
+	chd_data->maxrtt_in_rtt = 0;
+	chd_data->loss_compete = 0;
+	/*
+	 * Initialise the shadow_cwnd to be equal to snd_cwnd in case we are
+	 * competing with loss based flows from the start.
+	 */
+	chd_data->shadow_w = CCV(ccv, snd_cwnd);
+}
+
+static int
+chd_mod_init(void)
+{
+
+	ertt_id = khelp_get_id("ertt");
+	if (ertt_id <= 0) {
+		printf("%s: h_ertt module not found\n", __func__);
+		return (ENOENT);
+	}
+
+	chd_cc_algo.after_idle = newreno_cc_algo.after_idle;
+	chd_cc_algo.post_recovery = newreno_cc_algo.post_recovery;
+
+	return (0);
+}
+
+static int
+chd_loss_fair_handler(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	uint32_t new;
+
+	new = V_chd_loss_fair;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error == 0 && req->newptr != NULL) {
+		if (CAST_PTR_INT(req->newptr) > 1)
+			error = EINVAL;
+		else
+			V_chd_loss_fair = new;
+	}
+
+	return (error);
+}
+
+static int
+chd_pmax_handler(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	uint32_t new;
+
+	new = V_chd_pmax;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error == 0 && req->newptr != NULL) {
+		if (CAST_PTR_INT(req->newptr) == 0 ||
+		    CAST_PTR_INT(req->newptr) > 100)
+			error = EINVAL;
+		else
+			V_chd_pmax = new;
+	}
+
+	return (error);
+}
+
+static int
+chd_qthresh_handler(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	uint32_t new;
+
+	new = V_chd_qthresh;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error == 0 && req->newptr != NULL) {
+		if (CAST_PTR_INT(req->newptr) <= V_chd_qmin)
+			error = EINVAL;
+		else
+			V_chd_qthresh = new;
+	}
+
+	return (error);
+}
+
+SYSCTL_DECL(_net_inet_tcp_cc_chd);
+SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, chd, CTLFLAG_RW, NULL,
+    "CAIA Hamilton delay-based congestion control related settings");
+
+SYSCTL_VNET_PROC(_net_inet_tcp_cc_chd, OID_AUTO, loss_fair,
+    CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(chd_loss_fair), 1, &chd_loss_fair_handler,
+    "IU", "Flag to enable shadow window functionality.");
+
+SYSCTL_VNET_PROC(_net_inet_tcp_cc_chd, OID_AUTO, pmax,
+    CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(chd_pmax), 5, &chd_pmax_handler,
+    "IU", "Per RTT maximum backoff probability as a percentage");
+
+SYSCTL_VNET_PROC(_net_inet_tcp_cc_chd, OID_AUTO, queue_threshold,
+    CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(chd_qthresh), 20, &chd_qthresh_handler,
+    "IU", "Queueing congestion threshold in ticks");
+
+SYSCTL_VNET_UINT(_net_inet_tcp_cc_chd, OID_AUTO, queue_min,
+    CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(chd_qmin), 5,
+    "Minimum queueing delay threshold in ticks");
+
+SYSCTL_VNET_UINT(_net_inet_tcp_cc_chd,  OID_AUTO, use_max,
+    CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(chd_use_max), 1,
+    "Use the maximum RTT seen within the measurement period (RTT) "
+    "as the basic delay measurement for the algorithm.");
+
+DECLARE_CC_MODULE(chd, &chd_cc_algo);
+MODULE_DEPEND(chd, ertt, 1, 1, 1);