// SPDX-License-Identifier: GPL-2.0-only /* * TCP Low Priority (TCP-LP) * * TCP Low Priority is a distributed algorithm whose goal is to utilize only * the excess network bandwidth as compared to the ``fair share`` of * bandwidth as targeted by TCP. * * As of 2.6.13, Linux supports pluggable congestion control algorithms. * Due to the limitation of the API, we take the following changes from * the original TCP-LP implementation: * o We use newReno in most core CA handling. Only add some checking * within cong_avoid. * o Error correcting in remote HZ, therefore remote HZ will be keeped * on checking and updating. * o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since * OWD have a similar meaning as RTT. Also correct the buggy formular. * o Handle reaction for Early Congestion Indication (ECI) within * pkts_acked, as mentioned within pseudo code. * o OWD is handled in relative format, where local time stamp will in * tcp_time_stamp format. * * Original Author: * Aleksandar Kuzmanovic <akuzma@northwestern.edu> * Available from: * http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf * Original implementation for 2.4.19: * http://www-ece.rice.edu/networks/TCP-LP/ * * 2.6.x module Authors: * Wong Hoi Sing, Edison <hswong3i@gmail.com> * Hung Hing Lun, Mike <hlhung3i@gmail.com> * SourceForge project page: * http://tcp-lp-mod.sourceforge.net/ */ #include <linux/module.h> #include <net/tcp.h> /* resolution of owd */ #define LP_RESOL TCP_TS_HZ /** * enum tcp_lp_state * @LP_VALID_RHZ: is remote HZ valid? * @LP_VALID_OWD: is OWD valid? * @LP_WITHIN_THR: are we within threshold? * @LP_WITHIN_INF: are we within inference? * * TCP-LP's state flags. * We create this set of state flag mainly for debugging. */ enum tcp_lp_state { LP_VALID_RHZ = (1 << 0), LP_VALID_OWD = (1 << 1), LP_WITHIN_THR = (1 << 3), LP_WITHIN_INF = (1 << 4), }; /** * struct lp * @flag: TCP-LP state flag * @sowd: smoothed OWD << 3 * @owd_min: min OWD * @owd_max: max OWD * @owd_max_rsv: reserved max owd * @remote_hz: estimated remote HZ * @remote_ref_time: remote reference time * @local_ref_time: local reference time * @last_drop: time for last active drop * @inference: current inference * * TCP-LP's private struct. * We get the idea from original TCP-LP implementation where only left those we * found are really useful. */ struct lp { u32 flag; u32 sowd; u32 owd_min; u32 owd_max; u32 owd_max_rsv; u32 remote_hz; u32 remote_ref_time; u32 local_ref_time; u32 last_drop; u32 inference; }; /** * tcp_lp_init * @sk: socket to initialize congestion control algorithm for * * Init all required variables. * Clone the handling from Vegas module implementation. */ static void tcp_lp_init(struct sock *sk) { struct lp *lp = inet_csk_ca(sk); lp->flag = 0; lp->sowd = 0; lp->owd_min = 0xffffffff; lp->owd_max = 0; lp->owd_max_rsv = 0; lp->remote_hz = 0; lp->remote_ref_time = 0; lp->local_ref_time = 0; lp->last_drop = 0; lp->inference = 0; } /** * tcp_lp_cong_avoid * @sk: socket to avoid congesting * * Implementation of cong_avoid. * Will only call newReno CA when away from inference. * From TCP-LP's paper, this will be handled in additive increasement. */ static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked) { struct lp *lp = inet_csk_ca(sk); if (!(lp->flag & LP_WITHIN_INF)) tcp_reno_cong_avoid(sk, ack, acked); } /** * tcp_lp_remote_hz_estimator * @sk: socket which needs an estimate for the remote HZs * * Estimate remote HZ. * We keep on updating the estimated value, where original TCP-LP * implementation only guest it for once and use forever. */ static u32 tcp_lp_remote_hz_estimator(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct lp *lp = inet_csk_ca(sk); s64 rhz = lp->remote_hz << 6; /* remote HZ << 6 */ s64 m = 0; /* not yet record reference time * go away!! record it before come back!! */ if (lp->remote_ref_time == 0 || lp->local_ref_time == 0) goto out; /* we can't calc remote HZ with no different!! */ if (tp->rx_opt.rcv_tsval == lp->remote_ref_time || tp->rx_opt.rcv_tsecr == lp->local_ref_time) goto out; m = TCP_TS_HZ * (tp->rx_opt.rcv_tsval - lp->remote_ref_time) / (tp->rx_opt.rcv_tsecr - lp->local_ref_time); if (m < 0) m = -m; if (rhz > 0) { m -= rhz >> 6; /* m is now error in remote HZ est */ rhz += m; /* 63/64 old + 1/64 new */ } else rhz = m << 6; out: /* record time for successful remote HZ calc */ if ((rhz >> 6) > 0) lp->flag |= LP_VALID_RHZ; else lp->flag &= ~LP_VALID_RHZ; /* record reference time stamp */ lp->remote_ref_time = tp->rx_opt.rcv_tsval; lp->local_ref_time = tp->rx_opt.rcv_tsecr; return rhz >> 6; } /** * tcp_lp_owd_calculator * @sk: socket to calculate one way delay for * * Calculate one way delay (in relative format). * Original implement OWD as minus of remote time difference to local time * difference directly. As this time difference just simply equal to RTT, when * the network status is stable, remote RTT will equal to local RTT, and result * OWD into zero. * It seems to be a bug and so we fixed it. */ static u32 tcp_lp_owd_calculator(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct lp *lp = inet_csk_ca(sk); s64 owd = 0; lp->remote_hz = tcp_lp_remote_hz_estimator(sk); if (lp->flag & LP_VALID_RHZ) { owd = tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) - tp->rx_opt.rcv_tsecr * (LP_RESOL / TCP_TS_HZ); if (owd < 0) owd = -owd; } if (owd > 0) lp->flag |= LP_VALID_OWD; else lp->flag &= ~LP_VALID_OWD; return owd; } /** * tcp_lp_rtt_sample * @sk: socket to add a rtt sample to * @rtt: round trip time, which is ignored! * * Implementation or rtt_sample. * Will take the following action, * 1. calc OWD, * 2. record the min/max OWD, * 3. calc smoothed OWD (SOWD). * Most ideas come from the original TCP-LP implementation. */ static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt) { struct lp *lp = inet_csk_ca(sk); s64 mowd = tcp_lp_owd_calculator(sk); /* sorry that we don't have valid data */ if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD)) return; /* record the next min owd */ if (mowd < lp->owd_min) lp->owd_min = mowd; /* always forget the max of the max * we just set owd_max as one below it */ if (mowd > lp->owd_max) { if (mowd > lp->owd_max_rsv) { if (lp->owd_max_rsv == 0) lp->owd_max = mowd; else lp->owd_max = lp->owd_max_rsv; lp->owd_max_rsv = mowd; } else lp->owd_max = mowd; } /* calc for smoothed owd */ if (lp->sowd != 0) { mowd -= lp->sowd >> 3; /* m is now error in owd est */ lp->sowd += mowd; /* owd = 7/8 owd + 1/8 new */ } else lp->sowd = mowd << 3; /* take the measured time be owd */ } /** * tcp_lp_pkts_acked * @sk: socket requiring congestion avoidance calculations * * Implementation of pkts_acked. * Deal with active drop under Early Congestion Indication. * Only drop to half and 1 will be handle, because we hope to use back * newReno in increase case. * We work it out by following the idea from TCP-LP's paper directly */ static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample) { struct tcp_sock *tp = tcp_sk(sk); struct lp *lp = inet_csk_ca(sk); u32 now = tcp_time_stamp(tp); u32 delta; if (sample->rtt_us > 0) tcp_lp_rtt_sample(sk, sample->rtt_us); /* calc inference */ delta = now - tp->rx_opt.rcv_tsecr; if ((s32)delta > 0) lp->inference = 3 * delta; /* test if within inference */ if (lp->last_drop && (now - lp->last_drop < lp->inference)) lp->flag |= LP_WITHIN_INF; else lp->flag &= ~LP_WITHIN_INF; /* test if within threshold */ if (lp->sowd >> 3 < lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100) lp->flag |= LP_WITHIN_THR; else lp->flag &= ~LP_WITHIN_THR; pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag, tcp_snd_cwnd(tp), lp->remote_hz, lp->owd_min, lp->owd_max, lp->sowd >> 3); if (lp->flag & LP_WITHIN_THR) return; /* FIXME: try to reset owd_min and owd_max here * so decrease the chance the min/max is no longer suitable * and will usually within threshold when within inference */ lp->owd_min = lp->sowd >> 3; lp->owd_max = lp->sowd >> 2; lp->owd_max_rsv = lp->sowd >> 2; /* happened within inference * drop snd_cwnd into 1 */ if (lp->flag & LP_WITHIN_INF) tcp_snd_cwnd_set(tp, 1U); /* happened after inference * cut snd_cwnd into half */ else tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp) >> 1U, 1U)); /* record this drop time */ lp->last_drop = now; } static struct tcp_congestion_ops tcp_lp __read_mostly = { .init = tcp_lp_init, .ssthresh = tcp_reno_ssthresh, .undo_cwnd = tcp_reno_undo_cwnd, .cong_avoid = tcp_lp_cong_avoid, .pkts_acked = tcp_lp_pkts_acked, .owner = THIS_MODULE, .name = "lp" }; static int __init tcp_lp_register(void) { BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE); return tcp_register_congestion_control(&tcp_lp); } static void __exit tcp_lp_unregister(void) { tcp_unregister_congestion_control(&tcp_lp); } module_init(tcp_lp_register); module_exit(tcp_lp_unregister); MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("TCP Low Priority"