1 files changed, 309 insertions, 0 deletions
diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
new file mode 100644
index 000000000..c6e97141e
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+++ b/net/ipv4/tcp_westwood.c
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+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * TCP Westwood+: end-to-end bandwidth estimation for TCP
+ *
+ *      Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4
+ *
+ * Support at http://c3lab.poliba.it/index.php/Westwood
+ * Main references in literature:
+ *
+ * - Mascolo S, Casetti, M. Gerla et al.
+ *   "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001
+ *
+ * - A. Grieco, s. Mascolo
+ *   "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer
+ *     Comm. Review, 2004
+ *
+ * - A. Dell'Aera, L. Grieco, S. Mascolo.
+ *   "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving :
+ *    A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004
+ *
+ * Westwood+ employs end-to-end bandwidth measurement to set cwnd and
+ * ssthresh after packet loss. The probing phase is as the original Reno.
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/inet_diag.h>
+#include <net/tcp.h>
+
+/* TCP Westwood structure */
+struct westwood {
+	u32    bw_ns_est;        /* first bandwidth estimation..not too smoothed 8) */
+	u32    bw_est;           /* bandwidth estimate */
+	u32    rtt_win_sx;       /* here starts a new evaluation... */
+	u32    bk;
+	u32    snd_una;          /* used for evaluating the number of acked bytes */
+	u32    cumul_ack;
+	u32    accounted;
+	u32    rtt;
+	u32    rtt_min;          /* minimum observed RTT */
+	u8     first_ack;        /* flag which infers that this is the first ack */
+	u8     reset_rtt_min;    /* Reset RTT min to next RTT sample*/
+};
+
+/* TCP Westwood functions and constants */
+#define TCP_WESTWOOD_RTT_MIN   (HZ/20)	/* 50ms */
+#define TCP_WESTWOOD_INIT_RTT  (20*HZ)	/* maybe too conservative?! */
+
+/*
+ * @tcp_westwood_create
+ * This function initializes fields used in TCP Westwood+,
+ * it is called after the initial SYN, so the sequence numbers
+ * are correct but new passive connections we have no
+ * information about RTTmin at this time so we simply set it to
+ * TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative
+ * since in this way we're sure it will be updated in a consistent
+ * way as soon as possible. It will reasonably happen within the first
+ * RTT period of the connection lifetime.
+ */
+static void tcp_westwood_init(struct sock *sk)
+{
+	struct westwood *w = inet_csk_ca(sk);
+
+	w->bk = 0;
+	w->bw_ns_est = 0;
+	w->bw_est = 0;
+	w->accounted = 0;
+	w->cumul_ack = 0;
+	w->reset_rtt_min = 1;
+	w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
+	w->rtt_win_sx = tcp_jiffies32;
+	w->snd_una = tcp_sk(sk)->snd_una;
+	w->first_ack = 1;
+}
+
+/*
+ * @westwood_do_filter
+ * Low-pass filter. Implemented using constant coefficients.
+ */
+static inline u32 westwood_do_filter(u32 a, u32 b)
+{
+	return ((7 * a) + b) >> 3;
+}
+
+static void westwood_filter(struct westwood *w, u32 delta)
+{
+	/* If the filter is empty fill it with the first sample of bandwidth  */
+	if (w->bw_ns_est == 0 && w->bw_est == 0) {
+		w->bw_ns_est = w->bk / delta;
+		w->bw_est = w->bw_ns_est;
+	} else {
+		w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
+		w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
+	}
+}
+
+/*
+ * @westwood_pkts_acked
+ * Called after processing group of packets.
+ * but all westwood needs is the last sample of srtt.
+ */
+static void tcp_westwood_pkts_acked(struct sock *sk,
+				    const struct ack_sample *sample)
+{
+	struct westwood *w = inet_csk_ca(sk);
+
+	if (sample->rtt_us > 0)
+		w->rtt = usecs_to_jiffies(sample->rtt_us);
+}
+
+/*
+ * @westwood_update_window
+ * It updates RTT evaluation window if it is the right moment to do
+ * it. If so it calls filter for evaluating bandwidth.
+ */
+static void westwood_update_window(struct sock *sk)
+{
+	struct westwood *w = inet_csk_ca(sk);
+	s32 delta = tcp_jiffies32 - w->rtt_win_sx;
+
+	/* Initialize w->snd_una with the first acked sequence number in order
+	 * to fix mismatch between tp->snd_una and w->snd_una for the first
+	 * bandwidth sample
+	 */
+	if (w->first_ack) {
+		w->snd_una = tcp_sk(sk)->snd_una;
+		w->first_ack = 0;
+	}
+
+	/*
+	 * See if a RTT-window has passed.
+	 * Be careful since if RTT is less than
+	 * 50ms we don't filter but we continue 'building the sample'.
+	 * This minimum limit was chosen since an estimation on small
+	 * time intervals is better to avoid...
+	 * Obviously on a LAN we reasonably will always have
+	 * right_bound = left_bound + WESTWOOD_RTT_MIN
+	 */
+	if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {
+		westwood_filter(w, delta);
+
+		w->bk = 0;
+		w->rtt_win_sx = tcp_jiffies32;
+	}
+}
+
+static inline void update_rtt_min(struct westwood *w)
+{
+	if (w->reset_rtt_min) {
+		w->rtt_min = w->rtt;
+		w->reset_rtt_min = 0;
+	} else
+		w->rtt_min = min(w->rtt, w->rtt_min);
+}
+
+/*
+ * @westwood_fast_bw
+ * It is called when we are in fast path. In particular it is called when
+ * header prediction is successful. In such case in fact update is
+ * straight forward and doesn't need any particular care.
+ */
+static inline void westwood_fast_bw(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	struct westwood *w = inet_csk_ca(sk);
+
+	westwood_update_window(sk);
+
+	w->bk += tp->snd_una - w->snd_una;
+	w->snd_una = tp->snd_una;
+	update_rtt_min(w);
+}
+
+/*
+ * @westwood_acked_count
+ * This function evaluates cumul_ack for evaluating bk in case of
+ * delayed or partial acks.
+ */
+static inline u32 westwood_acked_count(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	struct westwood *w = inet_csk_ca(sk);
+
+	w->cumul_ack = tp->snd_una - w->snd_una;
+
+	/* If cumul_ack is 0 this is a dupack since it's not moving
+	 * tp->snd_una.
+	 */
+	if (!w->cumul_ack) {
+		w->accounted += tp->mss_cache;
+		w->cumul_ack = tp->mss_cache;
+	}
+
+	if (w->cumul_ack > tp->mss_cache) {
+		/* Partial or delayed ack */
+		if (w->accounted >= w->cumul_ack) {
+			w->accounted -= w->cumul_ack;
+			w->cumul_ack = tp->mss_cache;
+		} else {
+			w->cumul_ack -= w->accounted;
+			w->accounted = 0;
+		}
+	}
+
+	w->snd_una = tp->snd_una;
+
+	return w->cumul_ack;
+}
+
+/*
+ * TCP Westwood
+ * Here limit is evaluated as Bw estimation*RTTmin (for obtaining it
+ * in packets we use mss_cache). Rttmin is guaranteed to be >= 2
+ * so avoids ever returning 0.
+ */
+static u32 tcp_westwood_bw_rttmin(const struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	const struct westwood *w = inet_csk_ca(sk);
+
+	return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
+}
+
+static void tcp_westwood_ack(struct sock *sk, u32 ack_flags)
+{
+	if (ack_flags & CA_ACK_SLOWPATH) {
+		struct westwood *w = inet_csk_ca(sk);
+
+		westwood_update_window(sk);
+		w->bk += westwood_acked_count(sk);
+
+		update_rtt_min(w);
+		return;
+	}
+
+	westwood_fast_bw(sk);
+}
+
+static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct westwood *w = inet_csk_ca(sk);
+
+	switch (event) {
+	case CA_EVENT_COMPLETE_CWR:
+		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
+		break;
+	case CA_EVENT_LOSS:
+		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+		/* Update RTT_min when next ack arrives */
+		w->reset_rtt_min = 1;
+		break;
+	default:
+		/* don't care */
+		break;
+	}
+}
+
+/* Extract info for Tcp socket info provided via netlink. */
+static size_t tcp_westwood_info(struct sock *sk, u32 ext, int *attr,
+				union tcp_cc_info *info)
+{
+	const struct westwood *ca = inet_csk_ca(sk);
+
+	if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
+		info->vegas.tcpv_enabled = 1;
+		info->vegas.tcpv_rttcnt	= 0;
+		info->vegas.tcpv_rtt	= jiffies_to_usecs(ca->rtt);
+		info->vegas.tcpv_minrtt	= jiffies_to_usecs(ca->rtt_min);
+
+		*attr = INET_DIAG_VEGASINFO;
+		return sizeof(struct tcpvegas_info);
+	}
+	return 0;
+}
+
+static struct tcp_congestion_ops tcp_westwood __read_mostly = {
+	.init		= tcp_westwood_init,
+	.ssthresh	= tcp_reno_ssthresh,
+	.cong_avoid	= tcp_reno_cong_avoid,
+	.undo_cwnd      = tcp_reno_undo_cwnd,
+	.cwnd_event	= tcp_westwood_event,
+	.in_ack_event	= tcp_westwood_ack,
+	.get_info	= tcp_westwood_info,
+	.pkts_acked	= tcp_westwood_pkts_acked,
+
+	.owner		= THIS_MODULE,
+	.name		= "westwood"
+};
+
+static int __init tcp_westwood_register(void)
+{
+	BUILD_BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE);
+	return tcp_register_congestion_control(&tcp_westwood);
+}
+
+static void __exit tcp_westwood_unregister(void)
+{
+	tcp_unregister_congestion_control(&tcp_westwood);
+}
+
+module_init(tcp_westwood_register);
+module_exit(tcp_westwood_unregister);
+
+MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("TCP Westwood+");