// 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 <[email protected]>
* 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 <[email protected]>
* Hung Hing Lun, Mike <[email protected]>
* 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_ts(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");
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