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
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
|
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019 Facebook */
/* WARNING: This implemenation is not necessarily the same
* as the tcp_dctcp.c. The purpose is mainly for testing
* the kernel BPF logic.
*/
#include <stddef.h>
#include <linux/bpf.h>
#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/tcp.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "bpf_tcp_helpers.h"
char _license[] SEC("license") = "GPL";
volatile const char fallback[TCP_CA_NAME_MAX];
const char bpf_dctcp[] = "bpf_dctcp";
const char tcp_cdg[] = "cdg";
char cc_res[TCP_CA_NAME_MAX];
int tcp_cdg_res = 0;
int stg_result = 0;
struct {
__uint(type, BPF_MAP_TYPE_SK_STORAGE);
__uint(map_flags, BPF_F_NO_PREALLOC);
__type(key, int);
__type(value, int);
} sk_stg_map SEC(".maps");
#define DCTCP_MAX_ALPHA 1024U
struct dctcp {
__u32 old_delivered;
__u32 old_delivered_ce;
__u32 prior_rcv_nxt;
__u32 dctcp_alpha;
__u32 next_seq;
__u32 ce_state;
__u32 loss_cwnd;
};
static unsigned int dctcp_shift_g = 4; /* g = 1/2^4 */
static unsigned int dctcp_alpha_on_init = DCTCP_MAX_ALPHA;
static __always_inline void dctcp_reset(const struct tcp_sock *tp,
struct dctcp *ca)
{
ca->next_seq = tp->snd_nxt;
ca->old_delivered = tp->delivered;
ca->old_delivered_ce = tp->delivered_ce;
}
SEC("struct_ops/dctcp_init")
void BPF_PROG(dctcp_init, struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct dctcp *ca = inet_csk_ca(sk);
int *stg;
if (!(tp->ecn_flags & TCP_ECN_OK) && fallback[0]) {
/* Switch to fallback */
bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
(void *)fallback, sizeof(fallback));
/* Switch back to myself which the bpf trampoline
* stopped calling dctcp_init recursively.
*/
bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
(void *)bpf_dctcp, sizeof(bpf_dctcp));
/* Switch back to fallback */
bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
(void *)fallback, sizeof(fallback));
/* Expecting -ENOTSUPP for tcp_cdg_res */
tcp_cdg_res = bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
(void *)tcp_cdg, sizeof(tcp_cdg));
bpf_getsockopt(sk, SOL_TCP, TCP_CONGESTION,
(void *)cc_res, sizeof(cc_res));
return;
}
ca->prior_rcv_nxt = tp->rcv_nxt;
ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA);
ca->loss_cwnd = 0;
ca->ce_state = 0;
stg = bpf_sk_storage_get(&sk_stg_map, (void *)tp, NULL, 0);
if (stg) {
stg_result = *stg;
bpf_sk_storage_delete(&sk_stg_map, (void *)tp);
}
dctcp_reset(tp, ca);
}
SEC("struct_ops/dctcp_ssthresh")
__u32 BPF_PROG(dctcp_ssthresh, struct sock *sk)
{
struct dctcp *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
ca->loss_cwnd = tp->snd_cwnd;
return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U);
}
SEC("struct_ops/dctcp_update_alpha")
void BPF_PROG(dctcp_update_alpha, struct sock *sk, __u32 flags)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct dctcp *ca = inet_csk_ca(sk);
/* Expired RTT */
if (!before(tp->snd_una, ca->next_seq)) {
__u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce;
__u32 alpha = ca->dctcp_alpha;
/* alpha = (1 - g) * alpha + g * F */
alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
if (delivered_ce) {
__u32 delivered = tp->delivered - ca->old_delivered;
/* If dctcp_shift_g == 1, a 32bit value would overflow
* after 8 M packets.
*/
delivered_ce <<= (10 - dctcp_shift_g);
delivered_ce /= max(1U, delivered);
alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA);
}
ca->dctcp_alpha = alpha;
dctcp_reset(tp, ca);
}
}
static __always_inline void dctcp_react_to_loss(struct sock *sk)
{
struct dctcp *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
ca->loss_cwnd = tp->snd_cwnd;
tp->snd_ssthresh = max(tp->snd_cwnd >> 1U, 2U);
}
SEC("struct_ops/dctcp_state")
void BPF_PROG(dctcp_state, struct sock *sk, __u8 new_state)
{
if (new_state == TCP_CA_Recovery &&
new_state != BPF_CORE_READ_BITFIELD(inet_csk(sk), icsk_ca_state))
dctcp_react_to_loss(sk);
/* We handle RTO in dctcp_cwnd_event to ensure that we perform only
* one loss-adjustment per RTT.
*/
}
static __always_inline void dctcp_ece_ack_cwr(struct sock *sk, __u32 ce_state)
{
struct tcp_sock *tp = tcp_sk(sk);
if (ce_state == 1)
tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
else
tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
}
/* Minimal DCTP CE state machine:
*
* S: 0 <- last pkt was non-CE
* 1 <- last pkt was CE
*/
static __always_inline
void dctcp_ece_ack_update(struct sock *sk, enum tcp_ca_event evt,
__u32 *prior_rcv_nxt, __u32 *ce_state)
{
__u32 new_ce_state = (evt == CA_EVENT_ECN_IS_CE) ? 1 : 0;
if (*ce_state != new_ce_state) {
/* CE state has changed, force an immediate ACK to
* reflect the new CE state. If an ACK was delayed,
* send that first to reflect the prior CE state.
*/
if (inet_csk(sk)->icsk_ack.pending & ICSK_ACK_TIMER) {
dctcp_ece_ack_cwr(sk, *ce_state);
bpf_tcp_send_ack(sk, *prior_rcv_nxt);
}
inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
}
*prior_rcv_nxt = tcp_sk(sk)->rcv_nxt;
*ce_state = new_ce_state;
dctcp_ece_ack_cwr(sk, new_ce_state);
}
SEC("struct_ops/dctcp_cwnd_event")
void BPF_PROG(dctcp_cwnd_event, struct sock *sk, enum tcp_ca_event ev)
{
struct dctcp *ca = inet_csk_ca(sk);
switch (ev) {
case CA_EVENT_ECN_IS_CE:
case CA_EVENT_ECN_NO_CE:
dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state);
break;
case CA_EVENT_LOSS:
dctcp_react_to_loss(sk);
break;
default:
/* Don't care for the rest. */
break;
}
}
SEC("struct_ops/dctcp_cwnd_undo")
__u32 BPF_PROG(dctcp_cwnd_undo, struct sock *sk)
{
const struct dctcp *ca = inet_csk_ca(sk);
return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
}
extern void tcp_reno_cong_avoid(struct sock *sk, __u32 ack, __u32 acked) __ksym;
SEC("struct_ops/dctcp_reno_cong_avoid")
void BPF_PROG(dctcp_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
{
tcp_reno_cong_avoid(sk, ack, acked);
}
SEC(".struct_ops")
struct tcp_congestion_ops dctcp_nouse = {
.init = (void *)dctcp_init,
.set_state = (void *)dctcp_state,
.flags = TCP_CONG_NEEDS_ECN,
.name = "bpf_dctcp_nouse",
};
SEC(".struct_ops")
struct tcp_congestion_ops dctcp = {
.init = (void *)dctcp_init,
.in_ack_event = (void *)dctcp_update_alpha,
.cwnd_event = (void *)dctcp_cwnd_event,
.ssthresh = (void *)dctcp_ssthresh,
.cong_avoid = (void *)dctcp_cong_avoid,
.undo_cwnd = (void *)dctcp_cwnd_undo,
.set_state = (void *)dctcp_state,
.flags = TCP_CONG_NEEDS_ECN,
.name = "bpf_dctcp",
};
|
