/* * 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_time_stamp; 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, u32 cnt) { struct westwood *w = inet_csk_ca(sk); if (cnt > 0) w->rtt = tcp_sk(sk)->srtt >> 3; } /* * @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_time_stamp - 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_time_stamp; } } 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_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_FAST_ACK: westwood_fast_bw(sk); break; case CA_EVENT_COMPLETE_CWR: tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); break; case CA_EVENT_FRTO: tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); /* Update RTT_min when next ack arrives */ w->reset_rtt_min = 1; break; case CA_EVENT_SLOW_ACK: westwood_update_window(sk); w->bk += westwood_acked_count(sk); update_rtt_min(w); break; default: /* don't care */ break; } } /* Extract info for Tcp socket info provided via netlink. */ static void tcp_westwood_info(struct sock *sk, u32 ext, struct sk_buff *skb) { const struct westwood *ca = inet_csk_ca(sk); if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { struct rtattr *rta; struct tcpvegas_info *info; rta = __RTA_PUT(skb, INET_DIAG_VEGASINFO, sizeof(*info)); info = RTA_DATA(rta); info->tcpv_enabled = 1; info->tcpv_rttcnt = 0; info->tcpv_rtt = jiffies_to_usecs(ca->rtt); info->tcpv_minrtt = jiffies_to_usecs(ca->rtt_min); rtattr_failure: ; } } static struct tcp_congestion_ops tcp_westwood = { .init = tcp_westwood_init, .ssthresh = tcp_reno_ssthresh, .cong_avoid = tcp_reno_cong_avoid, .min_cwnd = tcp_westwood_bw_rttmin, .cwnd_event = tcp_westwood_event, .get_info = tcp_westwood_info, .pkts_acked = tcp_westwood_pkts_acked, .owner = THIS_MODULE, .name = "westwood" }; static int __init tcp_westwood_register(void) { 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+");