/*
* TCP Westwood+
*
* Angelo Dell'Aera: TCP Westwood+ support
*/
#include <linux/config.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/tcp_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 */
};
/* 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 tcp_sock *tp)
{
struct westwood *w = tcp_ca(tp);
w->bk = 0;
w->bw_ns_est = 0;
w->bw_est = 0;
w->accounted = 0;
w->cumul_ack = 0;
w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
w->rtt_win_sx = tcp_time_stamp;
w->snd_una = tp->snd_una;
}
/*
* @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 inline void westwood_filter(struct westwood *w, u32 delta)
{
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 tcp_sock *tp, u32 cnt)
{
struct westwood *w = tcp_ca(tp);
if (cnt > 0)
w->rtt = tp->srtt >> 3;
}
/*
* @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 tcp_sock *tp)
{
struct westwood *w = tcp_ca(tp);
s32 delta = tcp_time_stamp - w->rtt_win_sx;
/*
* 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_time_stamp;
}
}
/*
* @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 tcp_sock *tp)
{
struct westwood *w = tcp_ca(tp);
westwood_update_window(tp);
w->bk += tp->snd_una - w->snd_una;
w->snd_una = tp->snd_una;
w->rtt_min = min(w->rtt, w->rtt_min);
}
/*
* @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 tcp_sock *tp)
{
struct westwood *w = tcp_ca(tp);
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;
}
static inline u32 westwood_bw_rttmin(const struct tcp_sock *tp)
{
struct westwood *w = tcp_ca(tp);
return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
}
/*
* 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_cwnd_min(struct tcp_sock *tp)
{
return westwood_bw_rttmin(tp);
}
static void tcp_westwood_event(struct tcp_sock *tp, enum tcp_ca_event event)
{
struct westwood *w = tcp_ca(tp);
switch(event) {
case CA_EVENT_FAST_ACK:
westwood_fast_bw(tp);
break;
case CA_EVENT_COMPLETE_CWR:
tp->snd_cwnd = tp->snd_ssthresh = westwood_bw_rttmin(tp);
break;
case CA_EVENT_FRTO:
tp->snd_ssthresh = westwood_bw_rttmin(tp);
break;
case CA_EVENT_SLOW_ACK:
westwood_update_window(tp);
w->bk += westwood_acked_count(tp);
w->rtt_min = min(w->rtt, w->rtt_min);
break;
default:
/* don't care */
break;
}
}
/* Extract info for Tcp socket info provided via netlink. */
static void tcp_westwood_info(struct tcp_sock *tp, u32 ext,
struct sk_buff *skb)
{
const struct westwood *ca = tcp_ca(tp);
if (ext & (1<<(TCPDIAG_VEGASINFO-1))) {
struct rtattr *rta;
struct tcpvegas_info *info;
rta = __RTA_PUT(skb, TCPDIAG_VEGASINFO, sizeof(*info));
info = RTA_DATA(rta);
info->tcpv_enabled = 1;
info->tcpv_rttcnt = 0;
info->tcpv_rtt = jiffies_to_usecs(ca->rtt);
info->tcpv_minrtt = jiffies_to_usecs(ca->rtt_min);
rtattr_failure: ;
}
}
static struct tcp_congestion_ops tcp_westwood = {
.init = tcp_westwood_init,
.ssthresh = tcp_reno_ssthresh,
.cong_avoid = tcp_reno_cong_avoid,
.min_cwnd = tcp_westwood_cwnd_min,
.cwnd_event = tcp_westwood_event,
.get_info = tcp_westwood_info,
.pkts_acked = tcp_westwood_pkts_acked,
.owner = THIS_MODULE,
.name = "westwood"
};
static int __init tcp_westwood_register(void)
{
BUG_ON(sizeof(struct westwood) > TCP_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+");
