blob: 89f8fcf73f18f6e091881cc829861285c0c8f8b7 [file] [log] [blame]
Shriram Rajagopalanc3059be2012-02-05 13:51:32 +00001/*
2 * sch_plug.c Queue traffic until an explicit release command
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version
7 * 2 of the License, or (at your option) any later version.
8 *
9 * There are two ways to use this qdisc:
10 * 1. A simple "instantaneous" plug/unplug operation, by issuing an alternating
11 * sequence of TCQ_PLUG_BUFFER & TCQ_PLUG_RELEASE_INDEFINITE commands.
12 *
13 * 2. For network output buffering (a.k.a output commit) functionality.
14 * Output commit property is commonly used by applications using checkpoint
15 * based fault-tolerance to ensure that the checkpoint from which a system
16 * is being restored is consistent w.r.t outside world.
17 *
18 * Consider for e.g. Remus - a Virtual Machine checkpointing system,
19 * wherein a VM is checkpointed, say every 50ms. The checkpoint is replicated
20 * asynchronously to the backup host, while the VM continues executing the
21 * next epoch speculatively.
22 *
23 * The following is a typical sequence of output buffer operations:
24 * 1.At epoch i, start_buffer(i)
25 * 2. At end of epoch i (i.e. after 50ms):
26 * 2.1 Stop VM and take checkpoint(i).
27 * 2.2 start_buffer(i+1) and Resume VM
28 * 3. While speculatively executing epoch(i+1), asynchronously replicate
29 * checkpoint(i) to backup host.
30 * 4. When checkpoint_ack(i) is received from backup, release_buffer(i)
31 * Thus, this Qdisc would receive the following sequence of commands:
32 * TCQ_PLUG_BUFFER (epoch i)
33 * .. TCQ_PLUG_BUFFER (epoch i+1)
34 * ....TCQ_PLUG_RELEASE_ONE (epoch i)
35 * ......TCQ_PLUG_BUFFER (epoch i+2)
36 * ........
37 */
38
39#include <linux/module.h>
40#include <linux/types.h>
41#include <linux/kernel.h>
42#include <linux/errno.h>
43#include <linux/netdevice.h>
44#include <linux/skbuff.h>
45#include <net/pkt_sched.h>
46
47/*
48 * State of the queue, when used for network output buffering:
49 *
50 * plug(i+1) plug(i) head
51 * ------------------+--------------------+---------------->
52 * | |
53 * | |
54 * pkts_current_epoch| pkts_last_epoch |pkts_to_release
55 * ----------------->|<--------+--------->|+--------------->
56 * v v
57 *
58 */
59
60struct plug_sched_data {
61 /* If true, the dequeue function releases all packets
62 * from head to end of the queue. The queue turns into
63 * a pass-through queue for newly arriving packets.
64 */
65 bool unplug_indefinite;
66
67 /* Queue Limit in bytes */
68 u32 limit;
69
70 /* Number of packets (output) from the current speculatively
71 * executing epoch.
72 */
73 u32 pkts_current_epoch;
74
75 /* Number of packets corresponding to the recently finished
76 * epoch. These will be released when we receive a
77 * TCQ_PLUG_RELEASE_ONE command. This command is typically
78 * issued after committing a checkpoint at the target.
79 */
80 u32 pkts_last_epoch;
81
82 /*
83 * Number of packets from the head of the queue, that can
84 * be released (committed checkpoint).
85 */
86 u32 pkts_to_release;
87};
88
89static int plug_enqueue(struct sk_buff *skb, struct Qdisc *sch)
90{
91 struct plug_sched_data *q = qdisc_priv(sch);
92
93 if (likely(sch->qstats.backlog + skb->len <= q->limit)) {
94 if (!q->unplug_indefinite)
95 q->pkts_current_epoch++;
96 return qdisc_enqueue_tail(skb, sch);
97 }
98
99 return qdisc_reshape_fail(skb, sch);
100}
101
102static struct sk_buff *plug_dequeue(struct Qdisc *sch)
103{
104 struct plug_sched_data *q = qdisc_priv(sch);
105
106 if (qdisc_is_throttled(sch))
107 return NULL;
108
109 if (!q->unplug_indefinite) {
110 if (!q->pkts_to_release) {
111 /* No more packets to dequeue. Block the queue
112 * and wait for the next release command.
113 */
114 qdisc_throttled(sch);
115 return NULL;
116 }
117 q->pkts_to_release--;
118 }
119
120 return qdisc_dequeue_head(sch);
121}
122
123static int plug_init(struct Qdisc *sch, struct nlattr *opt)
124{
125 struct plug_sched_data *q = qdisc_priv(sch);
126
127 q->pkts_current_epoch = 0;
128 q->pkts_last_epoch = 0;
129 q->pkts_to_release = 0;
130 q->unplug_indefinite = false;
131
132 if (opt == NULL) {
133 /* We will set a default limit of 100 pkts (~150kB)
134 * in case tx_queue_len is not available. The
135 * default value is completely arbitrary.
136 */
137 u32 pkt_limit = qdisc_dev(sch)->tx_queue_len ? : 100;
138 q->limit = pkt_limit * psched_mtu(qdisc_dev(sch));
139 } else {
140 struct tc_plug_qopt *ctl = nla_data(opt);
141
142 if (nla_len(opt) < sizeof(*ctl))
143 return -EINVAL;
144
145 q->limit = ctl->limit;
146 }
147
148 qdisc_throttled(sch);
149 return 0;
150}
151
152/* Receives 4 types of messages:
153 * TCQ_PLUG_BUFFER: Inset a plug into the queue and
154 * buffer any incoming packets
155 * TCQ_PLUG_RELEASE_ONE: Dequeue packets from queue head
156 * to beginning of the next plug.
157 * TCQ_PLUG_RELEASE_INDEFINITE: Dequeue all packets from queue.
158 * Stop buffering packets until the next TCQ_PLUG_BUFFER
159 * command is received (just act as a pass-thru queue).
160 * TCQ_PLUG_LIMIT: Increase/decrease queue size
161 */
162static int plug_change(struct Qdisc *sch, struct nlattr *opt)
163{
164 struct plug_sched_data *q = qdisc_priv(sch);
165 struct tc_plug_qopt *msg;
166
167 if (opt == NULL)
168 return -EINVAL;
169
170 msg = nla_data(opt);
171 if (nla_len(opt) < sizeof(*msg))
172 return -EINVAL;
173
174 switch (msg->action) {
175 case TCQ_PLUG_BUFFER:
176 /* Save size of the current buffer */
177 q->pkts_last_epoch = q->pkts_current_epoch;
178 q->pkts_current_epoch = 0;
179 if (q->unplug_indefinite)
180 qdisc_throttled(sch);
181 q->unplug_indefinite = false;
182 break;
183 case TCQ_PLUG_RELEASE_ONE:
184 /* Add packets from the last complete buffer to the
185 * packets to be released set.
186 */
187 q->pkts_to_release += q->pkts_last_epoch;
188 q->pkts_last_epoch = 0;
189 qdisc_unthrottled(sch);
190 netif_schedule_queue(sch->dev_queue);
191 break;
192 case TCQ_PLUG_RELEASE_INDEFINITE:
193 q->unplug_indefinite = true;
194 q->pkts_to_release = 0;
195 q->pkts_last_epoch = 0;
196 q->pkts_current_epoch = 0;
197 qdisc_unthrottled(sch);
198 netif_schedule_queue(sch->dev_queue);
199 break;
200 case TCQ_PLUG_LIMIT:
201 /* Limit is supplied in bytes */
202 q->limit = msg->limit;
203 break;
204 default:
205 return -EINVAL;
206 }
207
208 return 0;
209}
210
Eric Dumazet2132cf62012-02-13 05:40:45 +0000211static struct Qdisc_ops plug_qdisc_ops __read_mostly = {
Shriram Rajagopalanc3059be2012-02-05 13:51:32 +0000212 .id = "plug",
213 .priv_size = sizeof(struct plug_sched_data),
214 .enqueue = plug_enqueue,
215 .dequeue = plug_dequeue,
216 .peek = qdisc_peek_head,
217 .init = plug_init,
218 .change = plug_change,
219 .owner = THIS_MODULE,
220};
221
222static int __init plug_module_init(void)
223{
224 return register_qdisc(&plug_qdisc_ops);
225}
226
227static void __exit plug_module_exit(void)
228{
229 unregister_qdisc(&plug_qdisc_ops);
230}
231module_init(plug_module_init)
232module_exit(plug_module_exit)
233MODULE_LICENSE("GPL");