Import a clean-room implementation of the VEGAS congestion control algorithm

based on the paper "TCP Vegas: end to end congestion avoidance on a global
internet" by Brakmo and Peterson. It is implemented as a kernel module
compatible with the recently committed modular congestion control framework.

VEGAS uses network delay as a congestion indicator and unlike regular loss-based
algorithms, attempts to keep the network operating with stable queuing delays
and no congestion losses. By keeping network buffers used along the path within
a set range, queuing delays are kept low while maintaining high throughput.

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

1 files changed, 308 insertions, 0 deletions

diff --git a/sys/netinet/cc/cc_vegas.c b/sys/netinet/cc/cc_vegas.c
new file mode 100644
index 000000000000..3643b58e57c9
--- /dev/null
+++ b/sys/netinet/cc/cc_vegas.c
@@ -0,0 +1,308 @@
+/*-
+ * Copyright (c) 2009-2010
+ *	Swinburne University of Technology, Melbourne, Australia
+ * Copyright (c) 2010 Lawrence Stewart <lstewart@freebsd.org>
+ * 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 Vegas congestion control algorithm for FreeBSD,
+ * based on L. S. Brakmo and L. L. Peterson, "TCP Vegas: end to end congestion
+ * avoidance on a global internet", IEEE J. Sel. Areas Commun., vol. 13, no. 8,
+ * pp. 1465-1480, Oct. 1995. The original Vegas duplicate ack policy has not
+ * been implemented, since clock ticks are not as course as they were (i.e.
+ * 500ms) when Vegas was designed. Also, packets are timed once per RTT as in
+ * the original paper.
+ *
+ * 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/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_VEGAS_RATE	0x01000000
+
+static void	vegas_ack_received(struct cc_var *ccv, uint16_t ack_type);
+static void	vegas_cb_destroy(struct cc_var *ccv);
+static int	vegas_cb_init(struct cc_var *ccv);
+static void	vegas_cong_signal(struct cc_var *ccv, uint32_t signal_type);
+static void	vegas_conn_init(struct cc_var *ccv);
+static int	vegas_mod_init(void);
+
+struct vegas {
+	int slow_start_toggle;
+};
+
+static int32_t ertt_id;
+
+static VNET_DEFINE(uint32_t, vegas_alpha) = 1;
+static VNET_DEFINE(uint32_t, vegas_beta) = 3;
+#define	V_vegas_alpha	VNET(vegas_alpha)
+#define	V_vegas_beta	VNET(vegas_beta)
+
+MALLOC_DECLARE(M_VEGAS);
+MALLOC_DEFINE(M_VEGAS, "vegas data",
+    "Per connection data required for the Vegas congestion control algorithm");
+
+struct cc_algo vegas_cc_algo = {
+	.name = "vegas",
+	.ack_received = vegas_ack_received,
+	.cb_destroy = vegas_cb_destroy,
+	.cb_init = vegas_cb_init,
+	.cong_signal = vegas_cong_signal,
+	.conn_init = vegas_conn_init,
+	.mod_init = vegas_mod_init
+};
+
+/*
+ * The vegas window adjustment is done once every RTT, as indicated by the
+ * ERTT_NEW_MEASUREMENT flag. This flag is reset once the new measurment data
+ * has been used.
+ */
+static void
+vegas_ack_received(struct cc_var *ccv, uint16_t ack_type)
+{
+	struct ertt *e_t;
+	struct vegas *vegas_data;
+	long actual_tx_rate, expected_tx_rate, ndiff;
+
+	e_t = khelp_get_osd(CCV(ccv, osd), ertt_id);
+	vegas_data = ccv->cc_data;
+
+	if (e_t->flags & ERTT_NEW_MEASUREMENT) { /* Once per RTT. */
+		if (e_t->minrtt && e_t->markedpkt_rtt) {
+			expected_tx_rate = e_t->marked_snd_cwnd / e_t->minrtt;
+			actual_tx_rate = e_t->bytes_tx_in_marked_rtt /
+			    e_t->markedpkt_rtt;
+			ndiff = (expected_tx_rate - actual_tx_rate) *
+			    e_t->minrtt / CCV(ccv, t_maxseg);
+
+			if (ndiff < V_vegas_alpha) {
+				if (CCV(ccv, snd_cwnd) <=
+				    CCV(ccv, snd_ssthresh)) {
+					vegas_data->slow_start_toggle =
+					    vegas_data->slow_start_toggle ?
+					    0 : 1;
+				} else {
+					vegas_data->slow_start_toggle = 0;
+					CCV(ccv, snd_cwnd) =
+					    min(CCV(ccv, snd_cwnd) +
+					    CCV(ccv, t_maxseg),
+					    TCP_MAXWIN << CCV(ccv, snd_scale));
+				}
+			} else if (ndiff > V_vegas_beta) {
+				/* Rate-based congestion. */
+				vegas_cong_signal(ccv, CC_VEGAS_RATE);
+				vegas_data->slow_start_toggle = 0;
+			}
+		}
+		e_t->flags &= ~ERTT_NEW_MEASUREMENT;
+	}
+
+	if (vegas_data->slow_start_toggle)
+		newreno_cc_algo.ack_received(ccv, ack_type);
+}
+
+static void
+vegas_cb_destroy(struct cc_var *ccv)
+{
+
+	if (ccv->cc_data != NULL)
+		free(ccv->cc_data, M_VEGAS);
+}
+
+static int
+vegas_cb_init(struct cc_var *ccv)
+{
+	struct vegas *vegas_data;
+
+	vegas_data = malloc(sizeof(struct vegas), M_VEGAS, M_NOWAIT);
+
+	if (vegas_data == NULL)
+		return (ENOMEM);
+
+	vegas_data->slow_start_toggle = 1;
+	ccv->cc_data = vegas_data;
+
+	return (0);
+}
+
+/*
+ * If congestion has been triggered triggered by the Vegas measured rates, it is
+ * handled here, otherwise it falls back to newreno's congestion handling.
+ */
+static void
+vegas_cong_signal(struct cc_var *ccv, uint32_t signal_type)
+{
+	struct vegas *vegas_data;
+	int presignalrecov;
+
+	vegas_data = ccv->cc_data;
+
+	if (IN_RECOVERY(CCV(ccv, t_flags)))
+		presignalrecov = 1;
+	else
+		presignalrecov = 0;
+
+	switch(signal_type) {
+	case CC_VEGAS_RATE:
+		if (!IN_RECOVERY(CCV(ccv, t_flags))) {
+			CCV(ccv, snd_cwnd) = max(2 * CCV(ccv, t_maxseg),
+			    CCV(ccv, snd_cwnd) - CCV(ccv, t_maxseg));
+			if (CCV(ccv, snd_cwnd) < CCV(ccv, snd_ssthresh))
+				/* Exit slow start. */
+				CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
+		}
+		break;
+
+	default:
+		newreno_cc_algo.cong_signal(ccv, signal_type);
+	}
+
+	if (IN_RECOVERY(CCV(ccv, t_flags)) && !presignalrecov)
+		vegas_data->slow_start_toggle =
+		    (CCV(ccv, snd_cwnd) < CCV(ccv, snd_ssthresh)) ? 1 : 0;
+}
+
+static void
+vegas_conn_init(struct cc_var *ccv)
+{
+	struct vegas *vegas_data;
+
+	vegas_data = ccv->cc_data;
+	vegas_data->slow_start_toggle = 1;
+}
+
+static int
+vegas_mod_init(void)
+{
+
+	ertt_id = khelp_get_id("ertt");
+	if (ertt_id <= 0) {
+		printf("%s: h_ertt module not found\n", __func__);
+		return (ENOENT);
+	}
+
+	vegas_cc_algo.after_idle = newreno_cc_algo.after_idle;
+	vegas_cc_algo.post_recovery = newreno_cc_algo.post_recovery;
+
+	return (0);
+}
+
+static int
+vegas_alpha_handler(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	uint32_t new;
+
+	new = V_vegas_alpha;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error == 0 && req->newptr != NULL) {
+		if (CAST_PTR_INT(req->newptr) < 1 ||
+		    CAST_PTR_INT(req->newptr) > V_vegas_beta)
+			error = EINVAL;
+		else
+			V_vegas_alpha = new;
+	}
+
+	return (error);
+}
+
+static int
+vegas_beta_handler(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	uint32_t new;
+
+	new = V_vegas_beta;
+	error = sysctl_handle_int(oidp, &new, 0, req);
+	if (error == 0 && req->newptr != NULL) {
+		if (CAST_PTR_INT(req->newptr) < 1 ||
+		    CAST_PTR_INT(req->newptr) < V_vegas_alpha)
+			 error = EINVAL;
+		else
+			V_vegas_beta = new;
+	}
+
+	return (error);
+}
+
+SYSCTL_DECL(_net_inet_tcp_cc_vegas);
+SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, vegas, CTLFLAG_RW, NULL,
+    "Vegas related settings");
+
+SYSCTL_VNET_PROC(_net_inet_tcp_cc_vegas, OID_AUTO, alpha,
+    CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(vegas_alpha), 1, &vegas_alpha_handler,
+    "IU", "vegas alpha, specified as number of \"buffers\" (0 < alpha < beta)");
+
+SYSCTL_VNET_PROC(_net_inet_tcp_cc_vegas, OID_AUTO, beta,
+    CTLTYPE_UINT|CTLFLAG_RW, &VNET_NAME(vegas_beta), 3, &vegas_beta_handler,
+    "IU", "vegas beta, specified as number of \"buffers\" (0 < alpha < beta)");
+
+DECLARE_CC_MODULE(vegas, &vegas_cc_algo);
+MODULE_DEPEND(vegas, ertt, 1, 1, 1);