cregit-Linux how code gets into the kernel

Release 4.11 net/sched/sch_plug.c

Directory: net/sched
/*
 * 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;

	
bool throttled;

	/* 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 sk_buff **to_free) { 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_drop(skb, sch, to_free); }

Contributors

PersonTokensPropCommitsCommitProp
Shriram Rajagopalan7489.16%133.33%
Eric Dumazet89.64%133.33%
Florian Westphal11.20%133.33%
Total83100.00%3100.00%


static struct sk_buff *plug_dequeue(struct Qdisc *sch) { struct plug_sched_data *q = qdisc_priv(sch); if (q->throttled) 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. */ q->throttled = true; return NULL; } q->pkts_to_release--; } return qdisc_dequeue_head(sch); }

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PersonTokensPropCommitsCommitProp
Shriram Rajagopalan6388.73%150.00%
Eric Dumazet811.27%150.00%
Total71100.00%2100.00%


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) { q->limit = qdisc_dev(sch)->tx_queue_len * 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; } q->throttled = true; return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Shriram Rajagopalan11592.74%133.33%
Eric Dumazet54.03%133.33%
Phil Sutter43.23%133.33%
Total124100.00%3100.00%

/* 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) q->throttled = true; 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; q->throttled = false; 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; q->throttled = false; 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; }

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PersonTokensPropCommitsCommitProp
Shriram Rajagopalan18992.65%150.00%
Eric Dumazet157.35%150.00%
Total204100.00%2100.00%

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, .reset = qdisc_reset_queue, .owner = THIS_MODULE, };
static int __init plug_module_init(void) { return register_qdisc(&plug_qdisc_ops); }

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Shriram Rajagopalan16100.00%1100.00%
Total16100.00%1100.00%


static void __exit plug_module_exit(void) { unregister_qdisc(&plug_qdisc_ops); }

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Shriram Rajagopalan15100.00%1100.00%
Total15100.00%1100.00%

module_init(plug_module_init) module_exit(plug_module_exit) MODULE_LICENSE("GPL");

Overall Contributors

PersonTokensPropCommitsCommitProp
Shriram Rajagopalan58491.97%114.29%
Eric Dumazet416.46%342.86%
Américo Wang50.79%114.29%
Phil Sutter40.63%114.29%
Florian Westphal10.16%114.29%
Total635100.00%7100.00%
Directory: net/sched
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