1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
|
// SPDX-License-Identifier: GPL-2.0
/* RTT/RTO calculation.
*
* Adapted from TCP for AF_RXRPC by David Howells (dhowells@redhat.com)
*
* https://tools.ietf.org/html/rfc6298
* https://tools.ietf.org/html/rfc1122#section-4.2.3.1
* http://ccr.sigcomm.org/archive/1995/jan95/ccr-9501-partridge87.pdf
*/
#include <linux/net.h>
#include "ar-internal.h"
#define RXRPC_RTO_MAX (120 * USEC_PER_SEC)
#define RXRPC_TIMEOUT_INIT ((unsigned int)(1 * MSEC_PER_SEC)) /* RFC6298 2.1 initial RTO value */
#define rxrpc_jiffies32 ((u32)jiffies) /* As rxrpc_jiffies32 */
static u32 rxrpc_rto_min_us(struct rxrpc_peer *peer)
{
return 200;
}
static u32 __rxrpc_set_rto(const struct rxrpc_peer *peer)
{
return (peer->srtt_us >> 3) + peer->rttvar_us;
}
static u32 rxrpc_bound_rto(u32 rto)
{
return min(rto, RXRPC_RTO_MAX);
}
/*
* Called to compute a smoothed rtt estimate. The data fed to this
* routine either comes from timestamps, or from segments that were
* known _not_ to have been retransmitted [see Karn/Partridge
* Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
* piece by Van Jacobson.
* NOTE: the next three routines used to be one big routine.
* To save cycles in the RFC 1323 implementation it was better to break
* it up into three procedures. -- erics
*/
static void rxrpc_rtt_estimator(struct rxrpc_peer *peer, long sample_rtt_us)
{
long m = sample_rtt_us; /* RTT */
u32 srtt = peer->srtt_us;
/* The following amusing code comes from Jacobson's
* article in SIGCOMM '88. Note that rtt and mdev
* are scaled versions of rtt and mean deviation.
* This is designed to be as fast as possible
* m stands for "measurement".
*
* On a 1990 paper the rto value is changed to:
* RTO = rtt + 4 * mdev
*
* Funny. This algorithm seems to be very broken.
* These formulae increase RTO, when it should be decreased, increase
* too slowly, when it should be increased quickly, decrease too quickly
* etc. I guess in BSD RTO takes ONE value, so that it is absolutely
* does not matter how to _calculate_ it. Seems, it was trap
* that VJ failed to avoid. 8)
*/
if (srtt != 0) {
m -= (srtt >> 3); /* m is now error in rtt est */
srtt += m; /* rtt = 7/8 rtt + 1/8 new */
if (m < 0) {
m = -m; /* m is now abs(error) */
m -= (peer->mdev_us >> 2); /* similar update on mdev */
/* This is similar to one of Eifel findings.
* Eifel blocks mdev updates when rtt decreases.
* This solution is a bit different: we use finer gain
* for mdev in this case (alpha*beta).
* Like Eifel it also prevents growth of rto,
* but also it limits too fast rto decreases,
* happening in pure Eifel.
*/
if (m > 0)
m >>= 3;
} else {
m -= (peer->mdev_us >> 2); /* similar update on mdev */
}
peer->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
if (peer->mdev_us > peer->mdev_max_us) {
peer->mdev_max_us = peer->mdev_us;
if (peer->mdev_max_us > peer->rttvar_us)
peer->rttvar_us = peer->mdev_max_us;
}
} else {
/* no previous measure. */
srtt = m << 3; /* take the measured time to be rtt */
peer->mdev_us = m << 1; /* make sure rto = 3*rtt */
peer->rttvar_us = max(peer->mdev_us, rxrpc_rto_min_us(peer));
peer->mdev_max_us = peer->rttvar_us;
}
peer->srtt_us = max(1U, srtt);
}
/*
* Calculate rto without backoff. This is the second half of Van Jacobson's
* routine referred to above.
*/
static void rxrpc_set_rto(struct rxrpc_peer *peer)
{
u32 rto;
/* 1. If rtt variance happened to be less 50msec, it is hallucination.
* It cannot be less due to utterly erratic ACK generation made
* at least by solaris and freebsd. "Erratic ACKs" has _nothing_
* to do with delayed acks, because at cwnd>2 true delack timeout
* is invisible. Actually, Linux-2.4 also generates erratic
* ACKs in some circumstances.
*/
rto = __rxrpc_set_rto(peer);
/* 2. Fixups made earlier cannot be right.
* If we do not estimate RTO correctly without them,
* all the algo is pure shit and should be replaced
* with correct one. It is exactly, which we pretend to do.
*/
/* NOTE: clamping at RXRPC_RTO_MIN is not required, current algo
* guarantees that rto is higher.
*/
peer->rto_us = rxrpc_bound_rto(rto);
}
static void rxrpc_ack_update_rtt(struct rxrpc_peer *peer, long rtt_us)
{
if (rtt_us < 0)
return;
//rxrpc_update_rtt_min(peer, rtt_us);
rxrpc_rtt_estimator(peer, rtt_us);
rxrpc_set_rto(peer);
/* RFC6298: only reset backoff on valid RTT measurement. */
peer->backoff = 0;
}
/*
* Add RTT information to cache. This is called in softirq mode and has
* exclusive access to the peer RTT data.
*/
void rxrpc_peer_add_rtt(struct rxrpc_call *call, enum rxrpc_rtt_rx_trace why,
int rtt_slot,
rxrpc_serial_t send_serial, rxrpc_serial_t resp_serial,
ktime_t send_time, ktime_t resp_time)
{
struct rxrpc_peer *peer = call->peer;
s64 rtt_us;
rtt_us = ktime_to_us(ktime_sub(resp_time, send_time));
if (rtt_us < 0)
return;
spin_lock(&peer->rtt_input_lock);
rxrpc_ack_update_rtt(peer, rtt_us);
if (peer->rtt_count < 3)
peer->rtt_count++;
spin_unlock(&peer->rtt_input_lock);
trace_rxrpc_rtt_rx(call, why, rtt_slot, send_serial, resp_serial,
peer->srtt_us >> 3, peer->rto_us);
}
/*
* Get the retransmission timeout to set in nanoseconds, backing it off each
* time we retransmit.
*/
ktime_t rxrpc_get_rto_backoff(struct rxrpc_peer *peer, bool retrans)
{
u64 timo_us;
u32 backoff = READ_ONCE(peer->backoff);
timo_us = peer->rto_us;
timo_us <<= backoff;
if (retrans && timo_us * 2 <= RXRPC_RTO_MAX)
WRITE_ONCE(peer->backoff, backoff + 1);
if (timo_us < 1)
timo_us = 1;
return ns_to_ktime(timo_us * NSEC_PER_USEC);
}
void rxrpc_peer_init_rtt(struct rxrpc_peer *peer)
{
peer->rto_us = RXRPC_TIMEOUT_INIT;
peer->mdev_us = RXRPC_TIMEOUT_INIT;
peer->backoff = 0;
//minmax_reset(&peer->rtt_min, rxrpc_jiffies32, ~0U);
}
|
