// SPDX-License-Identifier: GPL-2.0-only /* * 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 https://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.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_pkts_acked(struct sock *sk, const struct ack_sample *sample) { struct veno *veno = inet_csk_ca(sk); u32 vrtt; if (sample->rtt_us < 0) return; /* Never allow zero rtt or baseRTT */ vrtt = sample->rtt_us + 1; /* 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 acked) { struct tcp_sock *tp = tcp_sk(sk); struct veno *veno = inet_csk_ca(sk); if (!veno->doing_veno_now) { tcp_reno_cong_avoid(sk, ack, acked); return; } /* limited by applications */ if (!tcp_is_cwnd_limited(sk)) 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, acked); } else { u64 target_cwnd; u32 rtt; /* We have enough rtt samples, so, using the Veno * algorithm, we determine the state of the network. */ rtt = veno->minrtt; target_cwnd = (u64)tp->snd_cwnd * veno->basertt; target_cwnd <<= V_PARAM_SHIFT; do_div(target_cwnd, rtt); veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd; if (tcp_in_slow_start(tp)) { /* Slow start. */ acked = tcp_slow_start(tp, acked); if (!acked) goto done; } /* Congestion avoidance. */ if (veno->diff < beta) { /* In the "non-congestive state", increase cwnd * every rtt. */ tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked); } 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 += acked; } done: 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 __read_mostly = { .init = tcp_veno_init, .ssthresh = tcp_veno_ssthresh, .undo_cwnd = tcp_reno_undo_cwnd, .cong_avoid = tcp_veno_cong_avoid, .pkts_acked = tcp_veno_pkts_acked, .set_state = tcp_veno_state, .cwnd_event = tcp_veno_cwnd_event, .owner = THIS_MODULE, .name = "veno", }; static int __init tcp_veno_register(void) { BUILD_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");