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
|
/*
* sch_plug.c Queue traffic until an explicit release command
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* There are two ways to use this qdisc:
* 1. A simple "instantaneous" plug/unplug operation, by issuing an alternating
* sequence of TCQ_PLUG_BUFFER & TCQ_PLUG_RELEASE_INDEFINITE commands.
*
* 2. For network output buffering (a.k.a output commit) functionality.
* Output commit property is commonly used by applications using checkpoint
* based fault-tolerance to ensure that the checkpoint from which a system
* is being restored is consistent w.r.t outside world.
*
* Consider for e.g. Remus - a Virtual Machine checkpointing system,
* wherein a VM is checkpointed, say every 50ms. The checkpoint is replicated
* asynchronously to the backup host, while the VM continues executing the
* next epoch speculatively.
*
* The following is a typical sequence of output buffer operations:
* 1.At epoch i, start_buffer(i)
* 2. At end of epoch i (i.e. after 50ms):
* 2.1 Stop VM and take checkpoint(i).
* 2.2 start_buffer(i+1) and Resume VM
* 3. While speculatively executing epoch(i+1), asynchronously replicate
* checkpoint(i) to backup host.
* 4. When checkpoint_ack(i) is received from backup, release_buffer(i)
* Thus, this Qdisc would receive the following sequence of commands:
* TCQ_PLUG_BUFFER (epoch i)
* .. TCQ_PLUG_BUFFER (epoch i+1)
* ....TCQ_PLUG_RELEASE_ONE (epoch i)
* ......TCQ_PLUG_BUFFER (epoch i+2)
* ........
*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <net/pkt_sched.h>
/*
* State of the queue, when used for network output buffering:
*
* plug(i+1) plug(i) head
* ------------------+--------------------+---------------->
* | |
* | |
* pkts_current_epoch| pkts_last_epoch |pkts_to_release
* ----------------->|<--------+--------->|+--------------->
* v v
*
*/
struct plug_sched_data {
/* If true, the dequeue function releases all packets
* from head to end of the queue. The queue turns into
* a pass-through queue for newly arriving packets.
*/
bool unplug_indefinite;
/* Queue Limit in bytes */
u32 limit;
/* Number of packets (output) from the current speculatively
* executing epoch.
*/
u32 pkts_current_epoch;
/* Number of packets corresponding to the recently finished
* epoch. These will be released when we receive a
* TCQ_PLUG_RELEASE_ONE command. This command is typically
* issued after committing a checkpoint at the target.
*/
u32 pkts_last_epoch;
/*
* Number of packets from the head of the queue, that can
* be released (committed checkpoint).
*/
u32 pkts_to_release;
};
static int plug_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
struct plug_sched_data *q = qdisc_priv(sch);
if (likely(sch->qstats.backlog + skb->len <= q->limit)) {
if (!q->unplug_indefinite)
q->pkts_current_epoch++;
return qdisc_enqueue_tail(skb, sch);
}
return qdisc_reshape_fail(skb, sch);
}
static struct sk_buff *plug_dequeue(struct Qdisc *sch)
{
struct plug_sched_data *q = qdisc_priv(sch);
if (qdisc_is_throttled(sch))
return NULL;
if (!q->unplug_indefinite) {
if (!q->pkts_to_release) {
/* No more packets to dequeue. Block the queue
* and wait for the next release command.
*/
qdisc_throttled(sch);
return NULL;
}
q->pkts_to_release--;
}
return qdisc_dequeue_head(sch);
}
static int plug_init(struct Qdisc *sch, struct nlattr *opt)
{
struct plug_sched_data *q = qdisc_priv(sch);
q->pkts_current_epoch = 0;
q->pkts_last_epoch = 0;
q->pkts_to_release = 0;
q->unplug_indefinite = false;
if (opt == NULL) {
/* We will set a default limit of 100 pkts (~150kB)
* in case tx_queue_len is not available. The
* default value is completely arbitrary.
*/
u32 pkt_limit = qdisc_dev(sch)->tx_queue_len ? : 100;
q->limit = pkt_limit * psched_mtu(qdisc_dev(sch));
} else {
struct tc_plug_qopt *ctl = nla_data(opt);
if (nla_len(opt) < sizeof(*ctl))
return -EINVAL;
q->limit = ctl->limit;
}
qdisc_throttled(sch);
return 0;
}
/* Receives 4 types of messages:
* TCQ_PLUG_BUFFER: Inset a plug into the queue and
* buffer any incoming packets
* TCQ_PLUG_RELEASE_ONE: Dequeue packets from queue head
* to beginning of the next plug.
* TCQ_PLUG_RELEASE_INDEFINITE: Dequeue all packets from queue.
* Stop buffering packets until the next TCQ_PLUG_BUFFER
* command is received (just act as a pass-thru queue).
* TCQ_PLUG_LIMIT: Increase/decrease queue size
*/
static int plug_change(struct Qdisc *sch, struct nlattr *opt)
{
struct plug_sched_data *q = qdisc_priv(sch);
struct tc_plug_qopt *msg;
if (opt == NULL)
return -EINVAL;
msg = nla_data(opt);
if (nla_len(opt) < sizeof(*msg))
return -EINVAL;
switch (msg->action) {
case TCQ_PLUG_BUFFER:
/* Save size of the current buffer */
q->pkts_last_epoch = q->pkts_current_epoch;
q->pkts_current_epoch = 0;
if (q->unplug_indefinite)
qdisc_throttled(sch);
q->unplug_indefinite = false;
break;
case TCQ_PLUG_RELEASE_ONE:
/* Add packets from the last complete buffer to the
* packets to be released set.
*/
q->pkts_to_release += q->pkts_last_epoch;
q->pkts_last_epoch = 0;
qdisc_unthrottled(sch);
netif_schedule_queue(sch->dev_queue);
break;
case TCQ_PLUG_RELEASE_INDEFINITE:
q->unplug_indefinite = true;
q->pkts_to_release = 0;
q->pkts_last_epoch = 0;
q->pkts_current_epoch = 0;
qdisc_unthrottled(sch);
netif_schedule_queue(sch->dev_queue);
break;
case TCQ_PLUG_LIMIT:
/* Limit is supplied in bytes */
q->limit = msg->limit;
break;
default:
return -EINVAL;
}
return 0;
}
struct Qdisc_ops plug_qdisc_ops = {
.id = "plug",
.priv_size = sizeof(struct plug_sched_data),
.enqueue = plug_enqueue,
.dequeue = plug_dequeue,
.peek = qdisc_peek_head,
.init = plug_init,
.change = plug_change,
.owner = THIS_MODULE,
};
static int __init plug_module_init(void)
{
return register_qdisc(&plug_qdisc_ops);
}
static void __exit plug_module_exit(void)
{
unregister_qdisc(&plug_qdisc_ops);
}
module_init(plug_module_init)
module_exit(plug_module_exit)
MODULE_LICENSE("GPL");
|
