/* * 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 #include #include #include #include #include #include /* * 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; } static struct Qdisc_ops plug_qdisc_ops __read_mostly = { .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");