mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-24 05:04:00 +08:00
74cb879822
Vegas' slow start was only adding one MSS per RTT rather than one for every ack. Slow start behavior should now match Reno. Signed-off-by: Thomas Young <tyo@ee.mu.oz.au> Signed-off-by: David S. Miller <davem@davemloft.net>
390 lines
12 KiB
C
390 lines
12 KiB
C
/*
|
|
* TCP Vegas congestion control
|
|
*
|
|
* This is based on the congestion detection/avoidance scheme described in
|
|
* Lawrence S. Brakmo and Larry L. Peterson.
|
|
* "TCP Vegas: End to end congestion avoidance on a global internet."
|
|
* IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
|
|
* October 1995. Available from:
|
|
* ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps
|
|
*
|
|
* See http://www.cs.arizona.edu/xkernel/ for their implementation.
|
|
* The main aspects that distinguish this implementation from the
|
|
* Arizona Vegas implementation are:
|
|
* o We do not change the loss detection or recovery mechanisms of
|
|
* Linux in any way. Linux already recovers from losses quite well,
|
|
* using fine-grained timers, NewReno, and FACK.
|
|
* o To avoid the performance penalty imposed by increasing cwnd
|
|
* only every-other RTT during slow start, we increase during
|
|
* every RTT during slow start, just like Reno.
|
|
* o Largely to allow continuous cwnd growth during slow start,
|
|
* we use the rate at which ACKs come back as the "actual"
|
|
* rate, rather than the rate at which data is sent.
|
|
* o To speed convergence to the right rate, we set the cwnd
|
|
* to achieve the right ("actual") rate when we exit slow start.
|
|
* o To filter out the noise caused by delayed ACKs, we use the
|
|
* minimum RTT sample observed during the last RTT to calculate
|
|
* the actual rate.
|
|
* o When the sender re-starts from idle, it waits until it has
|
|
* received ACKs for an entire flight of new data before making
|
|
* a cwnd adjustment decision. The original Vegas implementation
|
|
* assumed senders never went idle.
|
|
*/
|
|
|
|
#include <linux/config.h>
|
|
#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 Vegas variables, in fixed-point representation
|
|
* with V_PARAM_SHIFT bits to the right of the binary point.
|
|
*/
|
|
#define V_PARAM_SHIFT 1
|
|
static int alpha = 1<<V_PARAM_SHIFT;
|
|
static int beta = 3<<V_PARAM_SHIFT;
|
|
static int gamma = 1<<V_PARAM_SHIFT;
|
|
|
|
module_param(alpha, int, 0644);
|
|
MODULE_PARM_DESC(alpha, "lower bound of packets in network (scale by 2)");
|
|
module_param(beta, int, 0644);
|
|
MODULE_PARM_DESC(beta, "upper bound of packets in network (scale by 2)");
|
|
module_param(gamma, int, 0644);
|
|
MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)");
|
|
|
|
|
|
/* Vegas variables */
|
|
struct vegas {
|
|
u32 beg_snd_nxt; /* right edge during last RTT */
|
|
u32 beg_snd_una; /* left edge during last RTT */
|
|
u32 beg_snd_cwnd; /* saves the size of the cwnd */
|
|
u8 doing_vegas_now;/* if true, do vegas 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 Vegas RTT measurements seen (in usec) */
|
|
};
|
|
|
|
/* There are several situations when we must "re-start" Vegas:
|
|
*
|
|
* 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)
|
|
*
|
|
* In these circumstances we cannot do a Vegas calculation at the
|
|
* end of the first RTT, because any calculation we do is using
|
|
* stale info -- both the saved cwnd and congestion feedback are
|
|
* stale.
|
|
*
|
|
* Instead we must wait until the completion of an RTT during
|
|
* which we actually receive ACKs.
|
|
*/
|
|
static inline void vegas_enable(struct sock *sk)
|
|
{
|
|
const struct tcp_sock *tp = tcp_sk(sk);
|
|
struct vegas *vegas = inet_csk_ca(sk);
|
|
|
|
/* Begin taking Vegas samples next time we send something. */
|
|
vegas->doing_vegas_now = 1;
|
|
|
|
/* Set the beginning of the next send window. */
|
|
vegas->beg_snd_nxt = tp->snd_nxt;
|
|
|
|
vegas->cntRTT = 0;
|
|
vegas->minRTT = 0x7fffffff;
|
|
}
|
|
|
|
/* Stop taking Vegas samples for now. */
|
|
static inline void vegas_disable(struct sock *sk)
|
|
{
|
|
struct vegas *vegas = inet_csk_ca(sk);
|
|
|
|
vegas->doing_vegas_now = 0;
|
|
}
|
|
|
|
static void tcp_vegas_init(struct sock *sk)
|
|
{
|
|
struct vegas *vegas = inet_csk_ca(sk);
|
|
|
|
vegas->baseRTT = 0x7fffffff;
|
|
vegas_enable(sk);
|
|
}
|
|
|
|
/* Do RTT sampling needed for Vegas.
|
|
* Basically we:
|
|
* o min-filter RTT samples from within an RTT to get the current
|
|
* propagation delay + queuing delay (we are min-filtering to try to
|
|
* avoid the effects of delayed ACKs)
|
|
* o min-filter RTT samples from a much longer window (forever for now)
|
|
* to find the propagation delay (baseRTT)
|
|
*/
|
|
static void tcp_vegas_rtt_calc(struct sock *sk, u32 usrtt)
|
|
{
|
|
struct vegas *vegas = inet_csk_ca(sk);
|
|
u32 vrtt = usrtt + 1; /* Never allow zero rtt or baseRTT */
|
|
|
|
/* Filter to find propagation delay: */
|
|
if (vrtt < vegas->baseRTT)
|
|
vegas->baseRTT = vrtt;
|
|
|
|
/* Find the min RTT during the last RTT to find
|
|
* the current prop. delay + queuing delay:
|
|
*/
|
|
vegas->minRTT = min(vegas->minRTT, vrtt);
|
|
vegas->cntRTT++;
|
|
}
|
|
|
|
static void tcp_vegas_state(struct sock *sk, u8 ca_state)
|
|
{
|
|
|
|
if (ca_state == TCP_CA_Open)
|
|
vegas_enable(sk);
|
|
else
|
|
vegas_disable(sk);
|
|
}
|
|
|
|
/*
|
|
* If the connection is idle and we are restarting,
|
|
* then we don't want to do any Vegas calculations
|
|
* until we get fresh RTT samples. So when we
|
|
* restart, we reset our Vegas state to a clean
|
|
* slate. After we get acks for this flight of
|
|
* packets, _then_ we can make Vegas calculations
|
|
* again.
|
|
*/
|
|
static void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event)
|
|
{
|
|
if (event == CA_EVENT_CWND_RESTART ||
|
|
event == CA_EVENT_TX_START)
|
|
tcp_vegas_init(sk);
|
|
}
|
|
|
|
static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
|
|
u32 seq_rtt, u32 in_flight, int flag)
|
|
{
|
|
struct tcp_sock *tp = tcp_sk(sk);
|
|
struct vegas *vegas = inet_csk_ca(sk);
|
|
|
|
if (!vegas->doing_vegas_now)
|
|
return tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
|
|
|
|
/* The key players are v_beg_snd_una and v_beg_snd_nxt.
|
|
*
|
|
* These are so named because they represent the approximate values
|
|
* of snd_una and snd_nxt at the beginning of the current RTT. More
|
|
* precisely, they represent the amount of data sent during the RTT.
|
|
* At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
|
|
* we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
|
|
* bytes of data have been ACKed during the course of the RTT, giving
|
|
* an "actual" rate of:
|
|
*
|
|
* (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
|
|
*
|
|
* Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
|
|
* because delayed ACKs can cover more than one segment, so they
|
|
* don't line up nicely with the boundaries of RTTs.
|
|
*
|
|
* Another unfortunate fact of life is that delayed ACKs delay the
|
|
* advance of the left edge of our send window, so that the number
|
|
* of bytes we send in an RTT is often less than our cwnd will allow.
|
|
* So we keep track of our cwnd separately, in v_beg_snd_cwnd.
|
|
*/
|
|
|
|
if (after(ack, vegas->beg_snd_nxt)) {
|
|
/* Do the Vegas once-per-RTT cwnd adjustment. */
|
|
u32 old_wnd, old_snd_cwnd;
|
|
|
|
|
|
/* Here old_wnd is essentially the window of data that was
|
|
* sent during the previous RTT, and has all
|
|
* been acknowledged in the course of the RTT that ended
|
|
* with the ACK we just received. Likewise, old_snd_cwnd
|
|
* is the cwnd during the previous RTT.
|
|
*/
|
|
old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /
|
|
tp->mss_cache;
|
|
old_snd_cwnd = vegas->beg_snd_cwnd;
|
|
|
|
/* Save the extent of the current window so we can use this
|
|
* at the end of the next RTT.
|
|
*/
|
|
vegas->beg_snd_una = vegas->beg_snd_nxt;
|
|
vegas->beg_snd_nxt = tp->snd_nxt;
|
|
vegas->beg_snd_cwnd = tp->snd_cwnd;
|
|
|
|
/* We do the Vegas calculations only if we got enough RTT
|
|
* samples that we can be reasonably sure that we got
|
|
* at least one RTT sample that wasn't from a delayed ACK.
|
|
* If we only had 2 samples total,
|
|
* then that means we're getting only 1 ACK per RTT, which
|
|
* means they're almost certainly delayed ACKs.
|
|
* If we have 3 samples, we should be OK.
|
|
*/
|
|
|
|
if (vegas->cntRTT <= 2) {
|
|
/* We don't have enough RTT samples to do the Vegas
|
|
* calculation, so we'll behave like Reno.
|
|
*/
|
|
tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);
|
|
} else {
|
|
u32 rtt, target_cwnd, diff;
|
|
|
|
/* We have enough RTT samples, so, using the Vegas
|
|
* algorithm, we determine if we should increase or
|
|
* decrease cwnd, and by how much.
|
|
*/
|
|
|
|
/* Pluck out the RTT we are using for the Vegas
|
|
* calculations. This is the min RTT seen during the
|
|
* last RTT. Taking the min filters out the effects
|
|
* of delayed ACKs, at the cost of noticing congestion
|
|
* a bit later.
|
|
*/
|
|
rtt = vegas->minRTT;
|
|
|
|
/* Calculate the cwnd we should have, if we weren't
|
|
* going too fast.
|
|
*
|
|
* This is:
|
|
* (actual rate in segments) * baseRTT
|
|
* We keep it as a fixed point number with
|
|
* V_PARAM_SHIFT bits to the right of the binary point.
|
|
*/
|
|
target_cwnd = ((old_wnd * vegas->baseRTT)
|
|
<< V_PARAM_SHIFT) / rtt;
|
|
|
|
/* Calculate the difference between the window we had,
|
|
* and the window we would like to have. This quantity
|
|
* is the "Diff" from the Arizona Vegas papers.
|
|
*
|
|
* Again, this is a fixed point number with
|
|
* V_PARAM_SHIFT bits to the right of the binary
|
|
* point.
|
|
*/
|
|
diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;
|
|
|
|
if (tp->snd_cwnd <= tp->snd_ssthresh) {
|
|
/* Slow start. */
|
|
if (diff > gamma) {
|
|
/* Going too fast. Time to slow down
|
|
* and switch to congestion avoidance.
|
|
*/
|
|
tp->snd_ssthresh = 2;
|
|
|
|
/* Set cwnd to match the actual rate
|
|
* exactly:
|
|
* cwnd = (actual rate) * baseRTT
|
|
* Then we add 1 because the integer
|
|
* truncation robs us of full link
|
|
* utilization.
|
|
*/
|
|
tp->snd_cwnd = min(tp->snd_cwnd,
|
|
(target_cwnd >>
|
|
V_PARAM_SHIFT)+1);
|
|
|
|
}
|
|
tcp_slow_start(tp);
|
|
} else {
|
|
/* Congestion avoidance. */
|
|
u32 next_snd_cwnd;
|
|
|
|
/* Figure out where we would like cwnd
|
|
* to be.
|
|
*/
|
|
if (diff > beta) {
|
|
/* The old window was too fast, so
|
|
* we slow down.
|
|
*/
|
|
next_snd_cwnd = old_snd_cwnd - 1;
|
|
} else if (diff < alpha) {
|
|
/* We don't have enough extra packets
|
|
* in the network, so speed up.
|
|
*/
|
|
next_snd_cwnd = old_snd_cwnd + 1;
|
|
} else {
|
|
/* Sending just as fast as we
|
|
* should be.
|
|
*/
|
|
next_snd_cwnd = old_snd_cwnd;
|
|
}
|
|
|
|
/* Adjust cwnd upward or downward, toward the
|
|
* desired value.
|
|
*/
|
|
if (next_snd_cwnd > tp->snd_cwnd)
|
|
tp->snd_cwnd++;
|
|
else if (next_snd_cwnd < tp->snd_cwnd)
|
|
tp->snd_cwnd--;
|
|
}
|
|
|
|
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. */
|
|
vegas->cntRTT = 0;
|
|
vegas->minRTT = 0x7fffffff;
|
|
}
|
|
/* Use normal slow start */
|
|
else if (tp->snd_cwnd <= tp->snd_ssthresh)
|
|
tcp_slow_start(tp);
|
|
|
|
}
|
|
|
|
/* Extract info for Tcp socket info provided via netlink. */
|
|
static void tcp_vegas_get_info(struct sock *sk, u32 ext,
|
|
struct sk_buff *skb)
|
|
{
|
|
const struct vegas *ca = inet_csk_ca(sk);
|
|
if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
|
|
struct tcpvegas_info *info;
|
|
|
|
info = RTA_DATA(__RTA_PUT(skb, INET_DIAG_VEGASINFO,
|
|
sizeof(*info)));
|
|
|
|
info->tcpv_enabled = ca->doing_vegas_now;
|
|
info->tcpv_rttcnt = ca->cntRTT;
|
|
info->tcpv_rtt = ca->baseRTT;
|
|
info->tcpv_minrtt = ca->minRTT;
|
|
rtattr_failure: ;
|
|
}
|
|
}
|
|
|
|
static struct tcp_congestion_ops tcp_vegas = {
|
|
.init = tcp_vegas_init,
|
|
.ssthresh = tcp_reno_ssthresh,
|
|
.cong_avoid = tcp_vegas_cong_avoid,
|
|
.min_cwnd = tcp_reno_min_cwnd,
|
|
.rtt_sample = tcp_vegas_rtt_calc,
|
|
.set_state = tcp_vegas_state,
|
|
.cwnd_event = tcp_vegas_cwnd_event,
|
|
.get_info = tcp_vegas_get_info,
|
|
|
|
.owner = THIS_MODULE,
|
|
.name = "vegas",
|
|
};
|
|
|
|
static int __init tcp_vegas_register(void)
|
|
{
|
|
BUG_ON(sizeof(struct vegas) > ICSK_CA_PRIV_SIZE);
|
|
tcp_register_congestion_control(&tcp_vegas);
|
|
return 0;
|
|
}
|
|
|
|
static void __exit tcp_vegas_unregister(void)
|
|
{
|
|
tcp_unregister_congestion_control(&tcp_vegas);
|
|
}
|
|
|
|
module_init(tcp_vegas_register);
|
|
module_exit(tcp_vegas_unregister);
|
|
|
|
MODULE_AUTHOR("Stephen Hemminger");
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_DESCRIPTION("TCP Vegas");
|