// 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 { … }; /* TCP Westwood functions and constants */ #define TCP_WESTWOOD_RTT_MIN … #define TCP_WESTWOOD_INIT_RTT … /* * @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) { … } /* * @westwood_do_filter * Low-pass filter. Implemented using constant coefficients. */ static inline u32 westwood_do_filter(u32 a, u32 b) { … } static void westwood_filter(struct westwood *w, u32 delta) { … } /* * @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) { … } /* * @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) { … } static inline void update_rtt_min(struct westwood *w) { … } /* * @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) { … } /* * @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) { … } /* * 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) { … } static void tcp_westwood_ack(struct sock *sk, u32 ack_flags) { … } static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event) { … } /* 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) { … } static struct tcp_congestion_ops tcp_westwood __read_mostly = …; static int __init tcp_westwood_register(void) { … } static void __exit tcp_westwood_unregister(void) { … } module_init(…) …; module_exit(tcp_westwood_unregister); MODULE_AUTHOR(…) …; MODULE_LICENSE(…) …; MODULE_DESCRIPTION(…) …;
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