--- /dev/null
+/*
+ * TCP Veno congestion control
+ *
+ * This is based on the congestion detection/avoidance scheme described in
+ * C. P. Fu, S. C. Liew.
+ * "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
+ * IEEE Journal on Selected Areas in Communication,
+ * Feb. 2003.
+ * See http://www.ntu.edu.sg/home5/ZHOU0022/papers/CPFu03a.pdf
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/inet_diag.h>
+
+#include <net/tcp.h>
+
+/* Default values of the Veno variables, in fixed-point representation
+ * with V_PARAM_SHIFT bits to the right of the binary point.
+ */
+#define V_PARAM_SHIFT 1
+static const int beta = 3 << V_PARAM_SHIFT;
+
+/* Veno variables */
+struct veno {
+ u8 doing_veno_now; /* if true, do veno 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 Veno rtt measurements seen (in usec) */
+ u32 inc; /* decide whether to increase cwnd */
+ u32 diff; /* calculate the diff rate */
+};
+
+/* There are several situations when we must "re-start" Veno:
+ *
+ * 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)
+ *
+ */
+static inline void veno_enable(struct sock *sk)
+{
+ struct veno *veno = inet_csk_ca(sk);
+
+ /* turn on Veno */
+ veno->doing_veno_now = 1;
+
+ veno->minrtt = 0x7fffffff;
+}
+
+static inline void veno_disable(struct sock *sk)
+{
+ struct veno *veno = inet_csk_ca(sk);
+
+ /* turn off Veno */
+ veno->doing_veno_now = 0;
+}
+
+static void tcp_veno_init(struct sock *sk)
+{
+ struct veno *veno = inet_csk_ca(sk);
+
+ veno->basertt = 0x7fffffff;
+ veno->inc = 1;
+ veno_enable(sk);
+}
+
+/* Do rtt sampling needed for Veno. */
+static void tcp_veno_rtt_calc(struct sock *sk, u32 usrtt)
+{
+ struct veno *veno = inet_csk_ca(sk);
+ u32 vrtt = usrtt + 1; /* Never allow zero rtt or basertt */
+
+ /* Filter to find propagation delay: */
+ if (vrtt < veno->basertt)
+ veno->basertt = vrtt;
+
+ /* Find the min rtt during the last rtt to find
+ * the current prop. delay + queuing delay:
+ */
+ veno->minrtt = min(veno->minrtt, vrtt);
+ veno->cntrtt++;
+}
+
+static void tcp_veno_state(struct sock *sk, u8 ca_state)
+{
+ if (ca_state == TCP_CA_Open)
+ veno_enable(sk);
+ else
+ veno_disable(sk);
+}
+
+/*
+ * If the connection is idle and we are restarting,
+ * then we don't want to do any Veno calculations
+ * until we get fresh rtt samples. So when we
+ * restart, we reset our Veno state to a clean
+ * state. After we get acks for this flight of
+ * packets, _then_ we can make Veno calculations
+ * again.
+ */
+static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
+{
+ if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
+ tcp_veno_init(sk);
+}
+
+static void tcp_veno_cong_avoid(struct sock *sk, u32 ack,
+ u32 seq_rtt, u32 in_flight, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct veno *veno = inet_csk_ca(sk);
+
+ if (!veno->doing_veno_now)
+ return tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
+
+ /* limited by applications */
+ if (!tcp_is_cwnd_limited(sk, in_flight))
+ return;
+
+ /* We do the Veno calculations only if we got enough rtt samples */
+ if (veno->cntrtt <= 2) {
+ /* We don't have enough rtt samples to do the Veno
+ * calculation, so we'll behave like Reno.
+ */
+ tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
+ } else {
+ u32 rtt, target_cwnd;
+
+ /* We have enough rtt samples, so, using the Veno
+ * algorithm, we determine the state of the network.
+ */
+
+ rtt = veno->minrtt;
+
+ target_cwnd = ((tp->snd_cwnd * veno->basertt)
+ << V_PARAM_SHIFT) / rtt;
+
+ veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
+
+ if (tp->snd_cwnd <= tp->snd_ssthresh) {
+ /* Slow start. */
+ tcp_slow_start(tp);
+ } else {
+ /* Congestion avoidance. */
+ if (veno->diff < beta) {
+ /* In the "non-congestive state", increase cwnd
+ * every rtt.
+ */
+ if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
+ if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+ tp->snd_cwnd++;
+ tp->snd_cwnd_cnt = 0;
+ } else
+ tp->snd_cwnd_cnt++;
+ } else {
+ /* In the "congestive state", increase cwnd
+ * every other rtt.
+ */
+ if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
+ if (veno->inc
+ && tp->snd_cwnd <
+ tp->snd_cwnd_clamp) {
+ tp->snd_cwnd++;
+ veno->inc = 0;
+ } else
+ veno->inc = 1;
+ tp->snd_cwnd_cnt = 0;
+ } else
+ tp->snd_cwnd_cnt++;
+ }
+
+ }
+ 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;
+ }
+ /* Wipe the slate clean for the next rtt. */
+ /* veno->cntrtt = 0; */
+ veno->minrtt = 0x7fffffff;
+}
+
+/* Veno MD phase */
+static u32 tcp_veno_ssthresh(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct veno *veno = inet_csk_ca(sk);
+
+ if (veno->diff < beta)
+ /* in "non-congestive state", cut cwnd by 1/5 */
+ return max(tp->snd_cwnd * 4 / 5, 2U);
+ else
+ /* in "congestive state", cut cwnd by 1/2 */
+ return max(tp->snd_cwnd >> 1U, 2U);
+}
+
+static struct tcp_congestion_ops tcp_veno = {
+ .init = tcp_veno_init,
+ .ssthresh = tcp_veno_ssthresh,
+ .cong_avoid = tcp_veno_cong_avoid,
+ .rtt_sample = tcp_veno_rtt_calc,
+ .set_state = tcp_veno_state,
+ .cwnd_event = tcp_veno_cwnd_event,
+
+ .owner = THIS_MODULE,
+ .name = "veno",
+};
+
+static int __init tcp_veno_register(void)
+{
+ BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
+ tcp_register_congestion_control(&tcp_veno);
+ return 0;
+}
+
+static void __exit tcp_veno_unregister(void)
+{
+ tcp_unregister_congestion_control(&tcp_veno);
+}
+
+module_init(tcp_veno_register);
+module_exit(tcp_veno_unregister);
+
+MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("TCP Veno");
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