232 lines
6.4 KiB
C
232 lines
6.4 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* sch_plug.c Queue traffic until an explicit release command
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*
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* There are two ways to use this qdisc:
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* 1. A simple "instantaneous" plug/unplug operation, by issuing an alternating
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* sequence of TCQ_PLUG_BUFFER & TCQ_PLUG_RELEASE_INDEFINITE commands.
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*
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* 2. For network output buffering (a.k.a output commit) functionality.
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* Output commit property is commonly used by applications using checkpoint
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* based fault-tolerance to ensure that the checkpoint from which a system
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* is being restored is consistent w.r.t outside world.
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*
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* Consider for e.g. Remus - a Virtual Machine checkpointing system,
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* wherein a VM is checkpointed, say every 50ms. The checkpoint is replicated
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* asynchronously to the backup host, while the VM continues executing the
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* next epoch speculatively.
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*
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* The following is a typical sequence of output buffer operations:
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* 1.At epoch i, start_buffer(i)
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* 2. At end of epoch i (i.e. after 50ms):
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* 2.1 Stop VM and take checkpoint(i).
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* 2.2 start_buffer(i+1) and Resume VM
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* 3. While speculatively executing epoch(i+1), asynchronously replicate
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* checkpoint(i) to backup host.
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* 4. When checkpoint_ack(i) is received from backup, release_buffer(i)
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* Thus, this Qdisc would receive the following sequence of commands:
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* TCQ_PLUG_BUFFER (epoch i)
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* .. TCQ_PLUG_BUFFER (epoch i+1)
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* ....TCQ_PLUG_RELEASE_ONE (epoch i)
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* ......TCQ_PLUG_BUFFER (epoch i+2)
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* ........
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*/
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/errno.h>
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#include <linux/netdevice.h>
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#include <linux/skbuff.h>
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#include <net/pkt_sched.h>
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/*
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* State of the queue, when used for network output buffering:
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*
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* plug(i+1) plug(i) head
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* ------------------+--------------------+---------------->
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* | |
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* | |
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* pkts_current_epoch| pkts_last_epoch |pkts_to_release
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* ----------------->|<--------+--------->|+--------------->
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* v v
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*
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*/
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struct plug_sched_data {
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/* If true, the dequeue function releases all packets
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* from head to end of the queue. The queue turns into
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* a pass-through queue for newly arriving packets.
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*/
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bool unplug_indefinite;
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bool throttled;
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/* Queue Limit in bytes */
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u32 limit;
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/* Number of packets (output) from the current speculatively
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* executing epoch.
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*/
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u32 pkts_current_epoch;
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/* Number of packets corresponding to the recently finished
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* epoch. These will be released when we receive a
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* TCQ_PLUG_RELEASE_ONE command. This command is typically
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* issued after committing a checkpoint at the target.
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*/
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u32 pkts_last_epoch;
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/*
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* Number of packets from the head of the queue, that can
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* be released (committed checkpoint).
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*/
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u32 pkts_to_release;
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};
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static int plug_enqueue(struct sk_buff *skb, struct Qdisc *sch,
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struct sk_buff **to_free)
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{
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struct plug_sched_data *q = qdisc_priv(sch);
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if (likely(sch->qstats.backlog + skb->len <= q->limit)) {
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if (!q->unplug_indefinite)
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q->pkts_current_epoch++;
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return qdisc_enqueue_tail(skb, sch);
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}
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return qdisc_drop(skb, sch, to_free);
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}
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static struct sk_buff *plug_dequeue(struct Qdisc *sch)
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{
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struct plug_sched_data *q = qdisc_priv(sch);
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if (q->throttled)
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return NULL;
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if (!q->unplug_indefinite) {
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if (!q->pkts_to_release) {
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/* No more packets to dequeue. Block the queue
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* and wait for the next release command.
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*/
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q->throttled = true;
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return NULL;
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}
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q->pkts_to_release--;
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}
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return qdisc_dequeue_head(sch);
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}
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static int plug_init(struct Qdisc *sch, struct nlattr *opt,
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struct netlink_ext_ack *extack)
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{
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struct plug_sched_data *q = qdisc_priv(sch);
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q->pkts_current_epoch = 0;
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q->pkts_last_epoch = 0;
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q->pkts_to_release = 0;
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q->unplug_indefinite = false;
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if (opt == NULL) {
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q->limit = qdisc_dev(sch)->tx_queue_len
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* psched_mtu(qdisc_dev(sch));
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} else {
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struct tc_plug_qopt *ctl = nla_data(opt);
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if (nla_len(opt) < sizeof(*ctl))
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return -EINVAL;
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q->limit = ctl->limit;
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}
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q->throttled = true;
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return 0;
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}
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/* Receives 4 types of messages:
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* TCQ_PLUG_BUFFER: Inset a plug into the queue and
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* buffer any incoming packets
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* TCQ_PLUG_RELEASE_ONE: Dequeue packets from queue head
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* to beginning of the next plug.
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* TCQ_PLUG_RELEASE_INDEFINITE: Dequeue all packets from queue.
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* Stop buffering packets until the next TCQ_PLUG_BUFFER
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* command is received (just act as a pass-thru queue).
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* TCQ_PLUG_LIMIT: Increase/decrease queue size
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*/
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static int plug_change(struct Qdisc *sch, struct nlattr *opt,
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struct netlink_ext_ack *extack)
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{
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struct plug_sched_data *q = qdisc_priv(sch);
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struct tc_plug_qopt *msg;
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if (opt == NULL)
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return -EINVAL;
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msg = nla_data(opt);
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if (nla_len(opt) < sizeof(*msg))
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return -EINVAL;
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switch (msg->action) {
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case TCQ_PLUG_BUFFER:
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/* Save size of the current buffer */
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q->pkts_last_epoch = q->pkts_current_epoch;
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q->pkts_current_epoch = 0;
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if (q->unplug_indefinite)
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q->throttled = true;
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q->unplug_indefinite = false;
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break;
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case TCQ_PLUG_RELEASE_ONE:
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/* Add packets from the last complete buffer to the
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* packets to be released set.
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*/
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q->pkts_to_release += q->pkts_last_epoch;
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q->pkts_last_epoch = 0;
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q->throttled = false;
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netif_schedule_queue(sch->dev_queue);
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break;
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case TCQ_PLUG_RELEASE_INDEFINITE:
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q->unplug_indefinite = true;
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q->pkts_to_release = 0;
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q->pkts_last_epoch = 0;
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q->pkts_current_epoch = 0;
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q->throttled = false;
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netif_schedule_queue(sch->dev_queue);
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break;
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case TCQ_PLUG_LIMIT:
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/* Limit is supplied in bytes */
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q->limit = msg->limit;
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break;
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default:
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return -EINVAL;
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}
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return 0;
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}
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static struct Qdisc_ops plug_qdisc_ops __read_mostly = {
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.id = "plug",
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.priv_size = sizeof(struct plug_sched_data),
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.enqueue = plug_enqueue,
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.dequeue = plug_dequeue,
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.peek = qdisc_peek_head,
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.init = plug_init,
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.change = plug_change,
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.reset = qdisc_reset_queue,
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.owner = THIS_MODULE,
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};
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static int __init plug_module_init(void)
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{
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return register_qdisc(&plug_qdisc_ops);
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}
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static void __exit plug_module_exit(void)
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{
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unregister_qdisc(&plug_qdisc_ops);
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}
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module_init(plug_module_init)
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module_exit(plug_module_exit)
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MODULE_LICENSE("GPL");
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