// 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 {
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_jiffies32;
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,
const struct ack_sample *sample)
{
struct westwood *w = inet_csk_ca(sk);
if (sample->rtt_us > 0)
w->rtt = usecs_to_jiffies(sample->rtt_us);
}
/*
* @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_jiffies32 - 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_jiffies32;
}
}
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_ack(struct sock *sk, u32 ack_flags)
{
if (ack_flags & CA_ACK_SLOWPATH) {
struct westwood *w = inet_csk_ca(sk);
westwood_update_window(sk);
w->bk += westwood_acked_count(sk);
update_rtt_min(w);
return;
}
westwood_fast_bw(sk);
}
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_COMPLETE_CWR:
tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
break;
case CA_EVENT_LOSS:
tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
/* Update RTT_min when next ack arrives */
w->reset_rtt_min = 1;
break;
default:
/* don't care */
break;
}
}
/* 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)
{
const struct westwood *ca = inet_csk_ca(sk);
if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
info->vegas.tcpv_enabled = 1;
info->vegas.tcpv_rttcnt = 0;
info->vegas.tcpv_rtt = jiffies_to_usecs(ca->rtt);
info->vegas.tcpv_minrtt = jiffies_to_usecs(ca->rtt_min);
*attr = INET_DIAG_VEGASINFO;
return sizeof(struct tcpvegas_info);
}
return 0;
}
static struct tcp_congestion_ops tcp_westwood __read_mostly = {
.init = tcp_westwood_init,
.ssthresh = tcp_reno_ssthresh,
.cong_avoid = tcp_reno_cong_avoid,
.undo_cwnd = tcp_reno_undo_cwnd,
.cwnd_event = tcp_westwood_event,
.in_ack_event = tcp_westwood_ack,
.get_info = tcp_westwood_info,
.pkts_acked = tcp_westwood_pkts_acked,
.owner = THIS_MODULE,
.name = "westwood"
};
static int __init tcp_westwood_register(void)
{
BUILD_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+");
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