[TCP] YeAH-TCP: algorithm implementation

YeAH-TCP is a sender-side high-speed enabled TCP congestion control
algorithm, which uses a mixed loss/delay approach to compute the
congestion window. It's design goals target high efficiency, internal,
RTT and Reno fairness, resilience to link loss while keeping network
elements load as low as possible.

For further details look here:
    http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf

Signed-off-by: Angelo P. Castellani <angelo.castellani@gmail.con>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 288 insertions, 0 deletions

diff --git a/net/ipv4/tcp_yeah.c b/net/ipv4/tcp_yeah.c
new file mode 100644
index 000000000000..815e020e98fe
--- /dev/null
+++ b/net/ipv4/tcp_yeah.c
@@ -0,0 +1,288 @@
+/*
+ *
+ *   YeAH TCP
+ *
+ * For further details look at:
+ *    http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
+ *
+ */
+
+#include "tcp_yeah.h"
+
+/* Default values of the Vegas variables, in fixed-point representation
+ * with V_PARAM_SHIFT bits to the right of the binary point.
+ */
+#define V_PARAM_SHIFT 1
+
+#define TCP_YEAH_ALPHA       80 //lin number of packets queued at the bottleneck
+#define TCP_YEAH_GAMMA        1 //lin fraction of queue to be removed per rtt
+#define TCP_YEAH_DELTA        3 //log minimum fraction of cwnd to be removed on loss
+#define TCP_YEAH_EPSILON      1 //log maximum fraction to be removed on early decongestion
+#define TCP_YEAH_PHY          8 //lin maximum delta from base
+#define TCP_YEAH_RHO         16 //lin minumum number of consecutive rtt to consider competition on loss
+#define TCP_YEAH_ZETA        50 //lin minimum number of state switchs to reset reno_count
+
+#define TCP_SCALABLE_AI_CNT	 100U
+
+/* YeAH variables */
+struct yeah {
+	/* Vegas */
+	u32	beg_snd_nxt;	/* right edge during last RTT */
+	u32	beg_snd_una;	/* left edge  during last RTT */
+	u32	beg_snd_cwnd;	/* saves the size of the cwnd */
+	u8	doing_vegas_now;/* if true, do vegas for this RTT */
+	u16	cntRTT;		/* # of RTTs measured within last RTT */
+	u32	minRTT;		/* min of RTTs measured within last RTT (in usec) */
+	u32	baseRTT;	/* the min of all Vegas RTT measurements seen (in usec) */
+
+	/* YeAH */
+	u32 lastQ;
+	u32 doing_reno_now;
+
+	u32 reno_count;
+	u32 fast_count;
+
+	u32 pkts_acked;
+};
+
+static void tcp_yeah_init(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct yeah *yeah = inet_csk_ca(sk);
+
+	tcp_vegas_init(sk);
+
+	yeah->doing_reno_now = 0;
+	yeah->lastQ = 0;
+
+	yeah->reno_count = 2;
+
+	/* Ensure the MD arithmetic works.  This is somewhat pedantic,
+	 * since I don't think we will see a cwnd this large. :) */
+	tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
+
+}
+
+
+static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	struct yeah *yeah = inet_csk_ca(sk);
+
+	if (icsk->icsk_ca_state == TCP_CA_Open)
+		yeah->pkts_acked = pkts_acked;
+}
+
+/* 64bit divisor, dividend and result. dynamic precision */
+static inline u64 div64_64(u64 dividend, u64 divisor)
+{
+	u32 d = divisor;
+
+	if (divisor > 0xffffffffULL) {
+		unsigned int shift = fls(divisor >> 32);
+
+		d = divisor >> shift;
+		dividend >>= shift;
+	}
+
+	/* avoid 64 bit division if possible */
+	if (dividend >> 32)
+		do_div(dividend, d);
+	else
+		dividend = (u32) dividend / d;
+
+	return dividend;
+}
+
+static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack,
+				 u32 seq_rtt, u32 in_flight, int flag)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct yeah *yeah = inet_csk_ca(sk);
+
+	if (!tcp_is_cwnd_limited(sk, in_flight))
+		return;
+
+	if (tp->snd_cwnd <= tp->snd_ssthresh) {
+		tcp_slow_start(tp);
+	} else if (!yeah->doing_reno_now) {
+		/* Scalable */
+
+		tp->snd_cwnd_cnt+=yeah->pkts_acked;
+		if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
+			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+				tp->snd_cwnd++;
+			tp->snd_cwnd_cnt = 0;
+		}
+
+		yeah->pkts_acked = 1;
+
+	} else {
+		/* Reno */
+
+		if (tp->snd_cwnd_cnt < tp->snd_cwnd)
+			tp->snd_cwnd_cnt++;
+
+		if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
+			tp->snd_cwnd++;
+			tp->snd_cwnd_cnt = 0;
+		}
+	}
+
+	/* The key players are v_beg_snd_una and v_beg_snd_nxt.
+	 *
+	 * These are so named because they represent the approximate values
+	 * of snd_una and snd_nxt at the beginning of the current RTT. More
+	 * precisely, they represent the amount of data sent during the RTT.
+	 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
+	 * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
+	 * bytes of data have been ACKed during the course of the RTT, giving
+	 * an "actual" rate of:
+	 *
+	 *     (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
+	 *
+	 * Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
+	 * because delayed ACKs can cover more than one segment, so they
+	 * don't line up yeahly with the boundaries of RTTs.
+	 *
+	 * Another unfortunate fact of life is that delayed ACKs delay the
+	 * advance of the left edge of our send window, so that the number
+	 * of bytes we send in an RTT is often less than our cwnd will allow.
+	 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
+	 */
+
+	if (after(ack, yeah->beg_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 (yeah->cntRTT > 2) {
+			u32 rtt;
+			u32 queue, maxqueue;
+
+			/* 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 = yeah->minRTT;
+
+			queue = (u32)div64_64((u64)tp->snd_cwnd * (rtt - yeah->baseRTT), rtt);
+
+			maxqueue = TCP_YEAH_ALPHA;
+
+			if (queue > maxqueue ||
+				    rtt - yeah->baseRTT > (yeah->baseRTT / TCP_YEAH_PHY)) {
+
+				if (queue > maxqueue && tp->snd_cwnd > yeah->reno_count) {
+					u32 reduction = min( queue / TCP_YEAH_GAMMA ,
+					                 tp->snd_cwnd >> TCP_YEAH_EPSILON );
+
+					tp->snd_cwnd -= reduction;
+
+					tp->snd_cwnd = max( tp->snd_cwnd, yeah->reno_count);
+
+					tp->snd_ssthresh = tp->snd_cwnd;
+			}
+
+				if (yeah->reno_count <= 2)
+					yeah->reno_count = max( tp->snd_cwnd>>1, 2U);
+				else
+					yeah->reno_count++;
+
+				yeah->doing_reno_now =
+					           min_t( u32, yeah->doing_reno_now + 1 , 0xffffff);
+
+			} else {
+				yeah->fast_count++;
+
+				if (yeah->fast_count > TCP_YEAH_ZETA) {
+					yeah->reno_count = 2;
+					yeah->fast_count = 0;
+				}
+
+				yeah->doing_reno_now = 0;
+			}
+
+			yeah->lastQ = queue;
+
+		}
+
+		/* Save the extent of the current window so we can use this
+		 * at the end of the next RTT.
+		 */
+		yeah->beg_snd_una  = yeah->beg_snd_nxt;
+		yeah->beg_snd_nxt  = tp->snd_nxt;
+		yeah->beg_snd_cwnd = tp->snd_cwnd;
+
+		/* Wipe the slate clean for the next RTT. */
+		yeah->cntRTT = 0;
+		yeah->minRTT = 0x7fffffff;
+	}
+}
+
+static u32 tcp_yeah_ssthresh(struct sock *sk) {
+	const struct tcp_sock *tp = tcp_sk(sk);
+	struct yeah *yeah = inet_csk_ca(sk);
+	u32 reduction;
+
+	if (yeah->doing_reno_now < TCP_YEAH_RHO) {
+		reduction = yeah->lastQ;
+
+		reduction = min( reduction, max(tp->snd_cwnd>>1, 2U) );
+
+		reduction = max( reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
+	} else
+		reduction = max(tp->snd_cwnd>>1,2U);
+
+	yeah->fast_count = 0;
+	yeah->reno_count = max(yeah->reno_count>>1, 2U);
+
+	return tp->snd_cwnd - reduction;
+}
+
+static struct tcp_congestion_ops tcp_yeah = {
+	.init		= tcp_yeah_init,
+	.ssthresh	= tcp_yeah_ssthresh,
+	.cong_avoid	= tcp_yeah_cong_avoid,
+	.min_cwnd	= tcp_reno_min_cwnd,
+	.rtt_sample	= tcp_vegas_rtt_calc,
+	.set_state	= tcp_vegas_state,
+	.cwnd_event	= tcp_vegas_cwnd_event,
+	.get_info	= tcp_vegas_get_info,
+	.pkts_acked	= tcp_yeah_pkts_acked,
+
+	.owner		= THIS_MODULE,
+	.name		= "yeah",
+};
+
+static int __init tcp_yeah_register(void)
+{
+	BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE);
+	tcp_register_congestion_control(&tcp_yeah);
+	return 0;
+}
+
+static void __exit tcp_yeah_unregister(void)
+{
+	tcp_unregister_congestion_control(&tcp_yeah);
+}
+
+module_init(tcp_yeah_register);
+module_exit(tcp_yeah_unregister);
+
+MODULE_AUTHOR("Angelo P. Castellani");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("YeAH TCP");