345 lines
8.7 KiB
C
345 lines
8.7 KiB
C
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/*
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* TCP Low Priority (TCP-LP)
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*
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* TCP Low Priority is a distributed algorithm whose goal is to utilize only
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* the excess network bandwidth as compared to the ``fair share`` of
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* bandwidth as targeted by TCP.
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*
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* As of 2.6.13, Linux supports pluggable congestion control algorithms.
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* Due to the limitation of the API, we take the following changes from
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* the original TCP-LP implementation:
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* o We use newReno in most core CA handling. Only add some checking
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* within cong_avoid.
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* o Error correcting in remote HZ, therefore remote HZ will be keeped
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* on checking and updating.
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* o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since
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* OWD have a similar meaning as RTT. Also correct the buggy formular.
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* o Handle reaction for Early Congestion Indication (ECI) within
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* pkts_acked, as mentioned within pseudo code.
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* o OWD is handled in relative format, where local time stamp will in
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* tcp_time_stamp format.
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*
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* Original Author:
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* Aleksandar Kuzmanovic <akuzma@northwestern.edu>
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* Available from:
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* http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf
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* Original implementation for 2.4.19:
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* http://www-ece.rice.edu/networks/TCP-LP/
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*
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* 2.6.x module Authors:
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* Wong Hoi Sing, Edison <hswong3i@gmail.com>
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* Hung Hing Lun, Mike <hlhung3i@gmail.com>
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* SourceForge project page:
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* http://tcp-lp-mod.sourceforge.net/
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*/
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#include <linux/module.h>
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#include <net/tcp.h>
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/* resolution of owd */
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#define LP_RESOL 1000
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/**
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* enum tcp_lp_state
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* @LP_VALID_RHZ: is remote HZ valid?
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* @LP_VALID_OWD: is OWD valid?
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* @LP_WITHIN_THR: are we within threshold?
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* @LP_WITHIN_INF: are we within inference?
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*
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* TCP-LP's state flags.
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* We create this set of state flag mainly for debugging.
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*/
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enum tcp_lp_state {
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LP_VALID_RHZ = (1 << 0),
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LP_VALID_OWD = (1 << 1),
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LP_WITHIN_THR = (1 << 3),
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LP_WITHIN_INF = (1 << 4),
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};
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/**
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* struct lp
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* @flag: TCP-LP state flag
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* @sowd: smoothed OWD << 3
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* @owd_min: min OWD
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* @owd_max: max OWD
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* @owd_max_rsv: resrved max owd
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* @remote_hz: estimated remote HZ
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* @remote_ref_time: remote reference time
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* @local_ref_time: local reference time
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* @last_drop: time for last active drop
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* @inference: current inference
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*
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* TCP-LP's private struct.
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* We get the idea from original TCP-LP implementation where only left those we
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* found are really useful.
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*/
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struct lp {
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u32 flag;
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u32 sowd;
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u32 owd_min;
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u32 owd_max;
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u32 owd_max_rsv;
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u32 remote_hz;
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u32 remote_ref_time;
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u32 local_ref_time;
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u32 last_drop;
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u32 inference;
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};
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/**
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* tcp_lp_init
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*
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* Init all required variables.
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* Clone the handling from Vegas module implementation.
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*/
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static void tcp_lp_init(struct sock *sk)
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{
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struct lp *lp = inet_csk_ca(sk);
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lp->flag = 0;
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lp->sowd = 0;
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lp->owd_min = 0xffffffff;
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lp->owd_max = 0;
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lp->owd_max_rsv = 0;
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lp->remote_hz = 0;
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lp->remote_ref_time = 0;
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lp->local_ref_time = 0;
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lp->last_drop = 0;
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lp->inference = 0;
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}
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/**
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* tcp_lp_cong_avoid
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*
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* Implementation of cong_avoid.
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* Will only call newReno CA when away from inference.
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* From TCP-LP's paper, this will be handled in additive increasement.
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*/
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static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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{
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struct lp *lp = inet_csk_ca(sk);
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if (!(lp->flag & LP_WITHIN_INF))
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tcp_reno_cong_avoid(sk, ack, acked);
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}
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/**
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* tcp_lp_remote_hz_estimator
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*
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* Estimate remote HZ.
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* We keep on updating the estimated value, where original TCP-LP
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* implementation only guest it for once and use forever.
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*/
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static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct lp *lp = inet_csk_ca(sk);
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s64 rhz = lp->remote_hz << 6; /* remote HZ << 6 */
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s64 m = 0;
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/* not yet record reference time
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* go away!! record it before come back!! */
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if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
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goto out;
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/* we can't calc remote HZ with no different!! */
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if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||
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tp->rx_opt.rcv_tsecr == lp->local_ref_time)
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goto out;
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m = HZ * (tp->rx_opt.rcv_tsval -
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lp->remote_ref_time) / (tp->rx_opt.rcv_tsecr -
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lp->local_ref_time);
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if (m < 0)
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m = -m;
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if (rhz > 0) {
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m -= rhz >> 6; /* m is now error in remote HZ est */
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rhz += m; /* 63/64 old + 1/64 new */
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} else
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rhz = m << 6;
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out:
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/* record time for successful remote HZ calc */
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if ((rhz >> 6) > 0)
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lp->flag |= LP_VALID_RHZ;
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else
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lp->flag &= ~LP_VALID_RHZ;
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/* record reference time stamp */
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lp->remote_ref_time = tp->rx_opt.rcv_tsval;
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lp->local_ref_time = tp->rx_opt.rcv_tsecr;
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return rhz >> 6;
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}
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/**
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* tcp_lp_owd_calculator
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*
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* Calculate one way delay (in relative format).
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* Original implement OWD as minus of remote time difference to local time
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* difference directly. As this time difference just simply equal to RTT, when
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* the network status is stable, remote RTT will equal to local RTT, and result
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* OWD into zero.
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* It seems to be a bug and so we fixed it.
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*/
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static u32 tcp_lp_owd_calculator(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct lp *lp = inet_csk_ca(sk);
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s64 owd = 0;
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lp->remote_hz = tcp_lp_remote_hz_estimator(sk);
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if (lp->flag & LP_VALID_RHZ) {
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owd =
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tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
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tp->rx_opt.rcv_tsecr * (LP_RESOL / HZ);
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if (owd < 0)
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owd = -owd;
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}
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if (owd > 0)
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lp->flag |= LP_VALID_OWD;
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else
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lp->flag &= ~LP_VALID_OWD;
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return owd;
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}
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/**
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* tcp_lp_rtt_sample
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*
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* Implementation or rtt_sample.
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* Will take the following action,
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* 1. calc OWD,
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* 2. record the min/max OWD,
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* 3. calc smoothed OWD (SOWD).
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* Most ideas come from the original TCP-LP implementation.
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*/
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static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt)
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{
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struct lp *lp = inet_csk_ca(sk);
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s64 mowd = tcp_lp_owd_calculator(sk);
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/* sorry that we don't have valid data */
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if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))
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return;
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/* record the next min owd */
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if (mowd < lp->owd_min)
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lp->owd_min = mowd;
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/* always forget the max of the max
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* we just set owd_max as one below it */
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if (mowd > lp->owd_max) {
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if (mowd > lp->owd_max_rsv) {
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if (lp->owd_max_rsv == 0)
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lp->owd_max = mowd;
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else
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lp->owd_max = lp->owd_max_rsv;
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lp->owd_max_rsv = mowd;
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} else
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lp->owd_max = mowd;
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}
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/* calc for smoothed owd */
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if (lp->sowd != 0) {
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mowd -= lp->sowd >> 3; /* m is now error in owd est */
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lp->sowd += mowd; /* owd = 7/8 owd + 1/8 new */
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} else
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lp->sowd = mowd << 3; /* take the measured time be owd */
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}
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/**
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* tcp_lp_pkts_acked
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*
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* Implementation of pkts_acked.
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* Deal with active drop under Early Congestion Indication.
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* Only drop to half and 1 will be handle, because we hope to use back
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* newReno in increase case.
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* We work it out by following the idea from TCP-LP's paper directly
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*/
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static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct lp *lp = inet_csk_ca(sk);
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u32 delta;
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if (sample->rtt_us > 0)
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tcp_lp_rtt_sample(sk, sample->rtt_us);
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/* calc inference */
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delta = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
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if ((s32)delta > 0)
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lp->inference = 3 * delta;
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/* test if within inference */
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if (lp->last_drop && (tcp_time_stamp - lp->last_drop < lp->inference))
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lp->flag |= LP_WITHIN_INF;
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else
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lp->flag &= ~LP_WITHIN_INF;
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/* test if within threshold */
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if (lp->sowd >> 3 <
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lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)
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lp->flag |= LP_WITHIN_THR;
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else
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lp->flag &= ~LP_WITHIN_THR;
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pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,
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tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,
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lp->sowd >> 3);
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if (lp->flag & LP_WITHIN_THR)
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return;
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/* FIXME: try to reset owd_min and owd_max here
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* so decrease the chance the min/max is no longer suitable
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* and will usually within threshold when whithin inference */
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lp->owd_min = lp->sowd >> 3;
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lp->owd_max = lp->sowd >> 2;
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lp->owd_max_rsv = lp->sowd >> 2;
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/* happened within inference
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* drop snd_cwnd into 1 */
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if (lp->flag & LP_WITHIN_INF)
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tp->snd_cwnd = 1U;
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/* happened after inference
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* cut snd_cwnd into half */
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else
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tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);
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/* record this drop time */
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lp->last_drop = tcp_time_stamp;
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}
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static struct tcp_congestion_ops tcp_lp __read_mostly = {
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.init = tcp_lp_init,
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.ssthresh = tcp_reno_ssthresh,
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.cong_avoid = tcp_lp_cong_avoid,
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.pkts_acked = tcp_lp_pkts_acked,
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.owner = THIS_MODULE,
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.name = "lp"
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};
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static int __init tcp_lp_register(void)
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{
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BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE);
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return tcp_register_congestion_control(&tcp_lp);
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}
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static void __exit tcp_lp_unregister(void)
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{
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tcp_unregister_congestion_control(&tcp_lp);
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}
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module_init(tcp_lp_register);
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module_exit(tcp_lp_unregister);
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MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("TCP Low Priority");
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