initial_commit

1 files changed, 339 insertions, 0 deletions

diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
new file mode 100644
index 00000000..80fa2bfd
--- /dev/null
+++ b/net/ipv4/tcp_vegas.c
@@ -0,0 +1,339 @@
+/*
+ * 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"
+
+static int alpha = 2;
+static int beta  = 4;
+static int gamma = 1;
+
+module_param(alpha, int, 0644);
+MODULE_PARM_DESC(alpha, "lower bound of packets in network");
+module_param(beta, int, 0644);
+MODULE_PARM_DESC(beta, "upper bound of packets in network");
+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 inline u32 tcp_vegas_ssthresh(struct tcp_sock *tp)
+{
+	return  min(tp->snd_ssthresh, tp->snd_cwnd-1);
+}
+
+static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct vegas *vegas = inet_csk_ca(sk);
+
+	if (!vegas->doing_vegas_now) {
+		tcp_reno_cong_avoid(sk, ack, in_flight);
+		return;
+	}
+
+	if (after(ack, vegas->beg_snd_nxt)) {
+		/* Do the Vegas once-per-RTT cwnd adjustment. */
+
+		/* Save the extent of the current window so we can use this
+		 * at the end of the next RTT.
+		 */
+		vegas->beg_snd_nxt  = tp->snd_nxt;
+
+		/* 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);
+		} else {
+			u32 rtt, diff;
+			u64 target_cwnd;
+
+			/* 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
+			 */
+			target_cwnd = tp->snd_cwnd * vegas->baseRTT / 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.
+			 */
+			diff = tp->snd_cwnd * (rtt-vegas->baseRTT) / vegas->baseRTT;
+
+			if (diff > gamma && tp->snd_cwnd <= tp->snd_ssthresh) {
+				/* Going too fast. Time to slow down
+				 * and switch to congestion avoidance.
+				 */
+
+				/* 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, (u32)target_cwnd+1);
+				tp->snd_ssthresh = tcp_vegas_ssthresh(tp);
+
+			} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
+				/* Slow start.  */
+				tcp_slow_start(tp);
+			} else {
+				/* Congestion avoidance. */
+
+				/* Figure out where we would like cwnd
+				 * to be.
+				 */
+				if (diff > beta) {
+					/* The old window was too fast, so
+					 * we slow down.
+					 */
+					tp->snd_cwnd--;
+					tp->snd_ssthresh
+						= tcp_vegas_ssthresh(tp);
+				} else if (diff < alpha) {
+					/* We don't have enough extra packets
+					 * in the network, so speed up.
+					 */
+					tp->snd_cwnd++;
+				} else {
+					/* Sending just as fast as we
+					 * should be.
+					 */
+				}
+			}
+
+			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;
+
+			tp->snd_ssthresh = tcp_current_ssthresh(sk);
+		}
+
+		/* 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 __read_mostly = {
+	.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");