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
|
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019 Facebook
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*
* Sample Host Bandwidth Manager (HBM) BPF program.
*
* A cgroup skb BPF egress program to limit cgroup output bandwidth.
* It uses a modified virtual token bucket queue to limit average
* egress bandwidth. The implementation uses credits instead of tokens.
* Negative credits imply that queueing would have happened (this is
* a virtual queue, so no queueing is done by it. However, queueing may
* occur at the actual qdisc (which is not used for rate limiting).
*
* This implementation uses 3 thresholds, one to start marking packets and
* the other two to drop packets:
* CREDIT
* - <--------------------------|------------------------> +
* | | | 0
* | Large pkt |
* | drop thresh |
* Small pkt drop Mark threshold
* thresh
*
* The effect of marking depends on the type of packet:
* a) If the packet is ECN enabled and it is a TCP packet, then the packet
* is ECN marked.
* b) If the packet is a TCP packet, then we probabilistically call tcp_cwr
* to reduce the congestion window. The current implementation uses a linear
* distribution (0% probability at marking threshold, 100% probability
* at drop threshold).
* c) If the packet is not a TCP packet, then it is dropped.
*
* If the credit is below the drop threshold, the packet is dropped. If it
* is a TCP packet, then it also calls tcp_cwr since packets dropped by
* by a cgroup skb BPF program do not automatically trigger a call to
* tcp_cwr in the current kernel code.
*
* This BPF program actually uses 2 drop thresholds, one threshold
* for larger packets (>= 120 bytes) and another for smaller packets. This
* protects smaller packets such as SYNs, ACKs, etc.
*
* The default bandwidth limit is set at 1Gbps but this can be changed by
* a user program through a shared BPF map. In addition, by default this BPF
* program does not limit connections using loopback. This behavior can be
* overwritten by the user program. There is also an option to calculate
* some statistics, such as percent of packets marked or dropped, which
* the user program can access.
*
* A latter patch provides such a program (hbm.c)
*/
#include "hbm_kern.h"
SEC("cgroup_skb/egress")
int _hbm_out_cg(struct __sk_buff *skb)
{
struct hbm_pkt_info pkti;
int len = skb->len;
unsigned int queue_index = 0;
unsigned long long curtime;
int credit;
signed long long delta = 0, zero = 0;
int max_credit = MAX_CREDIT;
bool congestion_flag = false;
bool drop_flag = false;
bool cwr_flag = false;
struct hbm_vqueue *qdp;
struct hbm_queue_stats *qsp = NULL;
int rv = ALLOW_PKT;
qsp = bpf_map_lookup_elem(&queue_stats, &queue_index);
if (qsp != NULL && !qsp->loopback && (skb->ifindex == 1))
return ALLOW_PKT;
hbm_get_pkt_info(skb, &pkti);
// We may want to account for the length of headers in len
// calculation, like ETH header + overhead, specially if it
// is a gso packet. But I am not doing it right now.
qdp = bpf_get_local_storage(&queue_state, 0);
if (!qdp)
return ALLOW_PKT;
else if (qdp->lasttime == 0)
hbm_init_vqueue(qdp, 1024);
curtime = bpf_ktime_get_ns();
// Begin critical section
bpf_spin_lock(&qdp->lock);
credit = qdp->credit;
delta = curtime - qdp->lasttime;
/* delta < 0 implies that another process with a curtime greater
* than ours beat us to the critical section and already added
* the new credit, so we should not add it ourselves
*/
if (delta > 0) {
qdp->lasttime = curtime;
credit += CREDIT_PER_NS(delta, qdp->rate);
if (credit > MAX_CREDIT)
credit = MAX_CREDIT;
}
credit -= len;
qdp->credit = credit;
bpf_spin_unlock(&qdp->lock);
// End critical section
// Check if we should update rate
if (qsp != NULL && (qsp->rate * 128) != qdp->rate) {
qdp->rate = qsp->rate * 128;
bpf_printk("Updating rate: %d (1sec:%llu bits)\n",
(int)qdp->rate,
CREDIT_PER_NS(1000000000, qdp->rate) * 8);
}
// Set flags (drop, congestion, cwr)
// Dropping => we are congested, so ignore congestion flag
if (credit < -DROP_THRESH ||
(len > LARGE_PKT_THRESH &&
credit < -LARGE_PKT_DROP_THRESH)) {
// Very congested, set drop flag
drop_flag = true;
} else if (credit < 0) {
// Congested, set congestion flag
if (pkti.ecn) {
if (credit < -MARK_THRESH)
congestion_flag = true;
else
congestion_flag = false;
} else {
congestion_flag = true;
}
}
if (congestion_flag) {
if (!bpf_skb_ecn_set_ce(skb)) {
if (len > LARGE_PKT_THRESH) {
// Problem if too many small packets?
drop_flag = true;
}
}
}
if (drop_flag)
rv = DROP_PKT;
hbm_update_stats(qsp, len, curtime, congestion_flag, drop_flag);
if (rv == DROP_PKT)
__sync_add_and_fetch(&(qdp->credit), len);
return rv;
}
char _license[] SEC("license") = "GPL";
|
