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TOMOYO Linux Cross Reference
Linux/net/sched/sch_plug.c

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  1 /*
  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 
 60 struct 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         bool throttled;
 68 
 69         /* Queue Limit in bytes */
 70         u32 limit;
 71 
 72         /* Number of packets (output) from the current speculatively
 73          * executing epoch.
 74          */
 75         u32 pkts_current_epoch;
 76 
 77         /* Number of packets corresponding to the recently finished
 78          * epoch. These will be released when we receive a
 79          * TCQ_PLUG_RELEASE_ONE command. This command is typically
 80          * issued after committing a checkpoint at the target.
 81          */
 82         u32 pkts_last_epoch;
 83 
 84         /*
 85          * Number of packets from the head of the queue, that can
 86          * be released (committed checkpoint).
 87          */
 88         u32 pkts_to_release;
 89 };
 90 
 91 static int plug_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 92                         struct sk_buff **to_free)
 93 {
 94         struct plug_sched_data *q = qdisc_priv(sch);
 95 
 96         if (likely(sch->qstats.backlog + skb->len <= q->limit)) {
 97                 if (!q->unplug_indefinite)
 98                         q->pkts_current_epoch++;
 99                 return qdisc_enqueue_tail(skb, sch);
100         }
101 
102         return qdisc_drop(skb, sch, to_free);
103 }
104 
105 static struct sk_buff *plug_dequeue(struct Qdisc *sch)
106 {
107         struct plug_sched_data *q = qdisc_priv(sch);
108 
109         if (q->throttled)
110                 return NULL;
111 
112         if (!q->unplug_indefinite) {
113                 if (!q->pkts_to_release) {
114                         /* No more packets to dequeue. Block the queue
115                          * and wait for the next release command.
116                          */
117                         q->throttled = true;
118                         return NULL;
119                 }
120                 q->pkts_to_release--;
121         }
122 
123         return qdisc_dequeue_head(sch);
124 }
125 
126 static int plug_init(struct Qdisc *sch, struct nlattr *opt)
127 {
128         struct plug_sched_data *q = qdisc_priv(sch);
129 
130         q->pkts_current_epoch = 0;
131         q->pkts_last_epoch = 0;
132         q->pkts_to_release = 0;
133         q->unplug_indefinite = false;
134 
135         if (opt == NULL) {
136                 q->limit = qdisc_dev(sch)->tx_queue_len
137                            * psched_mtu(qdisc_dev(sch));
138         } else {
139                 struct tc_plug_qopt *ctl = nla_data(opt);
140 
141                 if (nla_len(opt) < sizeof(*ctl))
142                         return -EINVAL;
143 
144                 q->limit = ctl->limit;
145         }
146 
147         q->throttled = true;
148         return 0;
149 }
150 
151 /* Receives 4 types of messages:
152  * TCQ_PLUG_BUFFER: Inset a plug into the queue and
153  *  buffer any incoming packets
154  * TCQ_PLUG_RELEASE_ONE: Dequeue packets from queue head
155  *   to beginning of the next plug.
156  * TCQ_PLUG_RELEASE_INDEFINITE: Dequeue all packets from queue.
157  *   Stop buffering packets until the next TCQ_PLUG_BUFFER
158  *   command is received (just act as a pass-thru queue).
159  * TCQ_PLUG_LIMIT: Increase/decrease queue size
160  */
161 static int plug_change(struct Qdisc *sch, struct nlattr *opt)
162 {
163         struct plug_sched_data *q = qdisc_priv(sch);
164         struct tc_plug_qopt *msg;
165 
166         if (opt == NULL)
167                 return -EINVAL;
168 
169         msg = nla_data(opt);
170         if (nla_len(opt) < sizeof(*msg))
171                 return -EINVAL;
172 
173         switch (msg->action) {
174         case TCQ_PLUG_BUFFER:
175                 /* Save size of the current buffer */
176                 q->pkts_last_epoch = q->pkts_current_epoch;
177                 q->pkts_current_epoch = 0;
178                 if (q->unplug_indefinite)
179                         q->throttled = true;
180                 q->unplug_indefinite = false;
181                 break;
182         case TCQ_PLUG_RELEASE_ONE:
183                 /* Add packets from the last complete buffer to the
184                  * packets to be released set.
185                  */
186                 q->pkts_to_release += q->pkts_last_epoch;
187                 q->pkts_last_epoch = 0;
188                 q->throttled = false;
189                 netif_schedule_queue(sch->dev_queue);
190                 break;
191         case TCQ_PLUG_RELEASE_INDEFINITE:
192                 q->unplug_indefinite = true;
193                 q->pkts_to_release = 0;
194                 q->pkts_last_epoch = 0;
195                 q->pkts_current_epoch = 0;
196                 q->throttled = false;
197                 netif_schedule_queue(sch->dev_queue);
198                 break;
199         case TCQ_PLUG_LIMIT:
200                 /* Limit is supplied in bytes */
201                 q->limit = msg->limit;
202                 break;
203         default:
204                 return -EINVAL;
205         }
206 
207         return 0;
208 }
209 
210 static struct Qdisc_ops plug_qdisc_ops __read_mostly = {
211         .id          =       "plug",
212         .priv_size   =       sizeof(struct plug_sched_data),
213         .enqueue     =       plug_enqueue,
214         .dequeue     =       plug_dequeue,
215         .peek        =       qdisc_peek_head,
216         .init        =       plug_init,
217         .change      =       plug_change,
218         .reset       =       qdisc_reset_queue,
219         .owner       =       THIS_MODULE,
220 };
221 
222 static int __init plug_module_init(void)
223 {
224         return register_qdisc(&plug_qdisc_ops);
225 }
226 
227 static void __exit plug_module_exit(void)
228 {
229         unregister_qdisc(&plug_qdisc_ops);
230 }
231 module_init(plug_module_init)
232 module_exit(plug_module_exit)
233 MODULE_LICENSE("GPL");
234 

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