linux/net/ipv4/tcp_veno.c
Neal Cardwell e73ebb0881 tcp: stretch ACK fixes prep
LRO, GRO, delayed ACKs, and middleboxes can cause "stretch ACKs" that
cover more than the RFC-specified maximum of 2 packets. These stretch
ACKs can cause serious performance shortfalls in common congestion
control algorithms that were designed and tuned years ago with
receiver hosts that were not using LRO or GRO, and were instead
politely ACKing every other packet.

This patch series fixes Reno and CUBIC to handle stretch ACKs.

This patch prepares for the upcoming stretch ACK bug fix patches. It
adds an "acked" parameter to tcp_cong_avoid_ai() to allow for future
fixes to tcp_cong_avoid_ai() to correctly handle stretch ACKs, and
changes all congestion control algorithms to pass in 1 for the ACKed
count. It also changes tcp_slow_start() to return the number of packet
ACK "credits" that were not processed in slow start mode, and can be
processed by the congestion control module in additive increase mode.

In future patches we will fix tcp_cong_avoid_ai() to handle stretch
ACKs, and fix Reno and CUBIC handling of stretch ACKs in slow start
and additive increase mode.

Reported-by: Eyal Perry <eyalpe@mellanox.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2015-01-28 22:18:37 -08:00

233 lines
5.6 KiB
C

/*
* TCP Veno congestion control
*
* This is based on the congestion detection/avoidance scheme described in
* C. P. Fu, S. C. Liew.
* "TCP Veno: TCP Enhancement for Transmission over Wireless Access Networks."
* IEEE Journal on Selected Areas in Communication,
* Feb. 2003.
* See http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Journal/J3.pdf
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/inet_diag.h>
#include <net/tcp.h>
/* Default values of the Veno variables, in fixed-point representation
* with V_PARAM_SHIFT bits to the right of the binary point.
*/
#define V_PARAM_SHIFT 1
static const int beta = 3 << V_PARAM_SHIFT;
/* Veno variables */
struct veno {
u8 doing_veno_now; /* if true, do veno for this rtt */
u16 cntrtt; /* # of rtts measured within last rtt */
u32 minrtt; /* min of rtts measured within last rtt (in usec) */
u32 basertt; /* the min of all Veno rtt measurements seen (in usec) */
u32 inc; /* decide whether to increase cwnd */
u32 diff; /* calculate the diff rate */
};
/* There are several situations when we must "re-start" Veno:
*
* o when a connection is established
* o after an RTO
* o after fast recovery
* o when we send a packet and there is no outstanding
* unacknowledged data (restarting an idle connection)
*
*/
static inline void veno_enable(struct sock *sk)
{
struct veno *veno = inet_csk_ca(sk);
/* turn on Veno */
veno->doing_veno_now = 1;
veno->minrtt = 0x7fffffff;
}
static inline void veno_disable(struct sock *sk)
{
struct veno *veno = inet_csk_ca(sk);
/* turn off Veno */
veno->doing_veno_now = 0;
}
static void tcp_veno_init(struct sock *sk)
{
struct veno *veno = inet_csk_ca(sk);
veno->basertt = 0x7fffffff;
veno->inc = 1;
veno_enable(sk);
}
/* Do rtt sampling needed for Veno. */
static void tcp_veno_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
{
struct veno *veno = inet_csk_ca(sk);
u32 vrtt;
if (rtt_us < 0)
return;
/* Never allow zero rtt or baseRTT */
vrtt = rtt_us + 1;
/* Filter to find propagation delay: */
if (vrtt < veno->basertt)
veno->basertt = vrtt;
/* Find the min rtt during the last rtt to find
* the current prop. delay + queuing delay:
*/
veno->minrtt = min(veno->minrtt, vrtt);
veno->cntrtt++;
}
static void tcp_veno_state(struct sock *sk, u8 ca_state)
{
if (ca_state == TCP_CA_Open)
veno_enable(sk);
else
veno_disable(sk);
}
/*
* If the connection is idle and we are restarting,
* then we don't want to do any Veno calculations
* until we get fresh rtt samples. So when we
* restart, we reset our Veno state to a clean
* state. After we get acks for this flight of
* packets, _then_ we can make Veno calculations
* again.
*/
static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event)
{
if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START)
tcp_veno_init(sk);
}
static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
struct tcp_sock *tp = tcp_sk(sk);
struct veno *veno = inet_csk_ca(sk);
if (!veno->doing_veno_now) {
tcp_reno_cong_avoid(sk, ack, acked);
return;
}
/* limited by applications */
if (!tcp_is_cwnd_limited(sk))
return;
/* We do the Veno calculations only if we got enough rtt samples */
if (veno->cntrtt <= 2) {
/* We don't have enough rtt samples to do the Veno
* calculation, so we'll behave like Reno.
*/
tcp_reno_cong_avoid(sk, ack, acked);
} else {
u64 target_cwnd;
u32 rtt;
/* We have enough rtt samples, so, using the Veno
* algorithm, we determine the state of the network.
*/
rtt = veno->minrtt;
target_cwnd = (u64)tp->snd_cwnd * veno->basertt;
target_cwnd <<= V_PARAM_SHIFT;
do_div(target_cwnd, rtt);
veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
if (tp->snd_cwnd <= tp->snd_ssthresh) {
/* Slow start. */
tcp_slow_start(tp, acked);
} else {
/* Congestion avoidance. */
if (veno->diff < beta) {
/* In the "non-congestive state", increase cwnd
* every rtt.
*/
tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1);
} else {
/* In the "congestive state", increase cwnd
* every other rtt.
*/
if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
if (veno->inc &&
tp->snd_cwnd < tp->snd_cwnd_clamp) {
tp->snd_cwnd++;
veno->inc = 0;
} else
veno->inc = 1;
tp->snd_cwnd_cnt = 0;
} else
tp->snd_cwnd_cnt++;
}
}
if (tp->snd_cwnd < 2)
tp->snd_cwnd = 2;
else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
tp->snd_cwnd = tp->snd_cwnd_clamp;
}
/* Wipe the slate clean for the next rtt. */
/* veno->cntrtt = 0; */
veno->minrtt = 0x7fffffff;
}
/* Veno MD phase */
static u32 tcp_veno_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct veno *veno = inet_csk_ca(sk);
if (veno->diff < beta)
/* in "non-congestive state", cut cwnd by 1/5 */
return max(tp->snd_cwnd * 4 / 5, 2U);
else
/* in "congestive state", cut cwnd by 1/2 */
return max(tp->snd_cwnd >> 1U, 2U);
}
static struct tcp_congestion_ops tcp_veno __read_mostly = {
.init = tcp_veno_init,
.ssthresh = tcp_veno_ssthresh,
.cong_avoid = tcp_veno_cong_avoid,
.pkts_acked = tcp_veno_pkts_acked,
.set_state = tcp_veno_state,
.cwnd_event = tcp_veno_cwnd_event,
.owner = THIS_MODULE,
.name = "veno",
};
static int __init tcp_veno_register(void)
{
BUILD_BUG_ON(sizeof(struct veno) > ICSK_CA_PRIV_SIZE);
tcp_register_congestion_control(&tcp_veno);
return 0;
}
static void __exit tcp_veno_unregister(void)
{
tcp_unregister_congestion_control(&tcp_veno);
}
module_init(tcp_veno_register);
module_exit(tcp_veno_unregister);
MODULE_AUTHOR("Bin Zhou, Cheng Peng Fu");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP Veno");