Fall 2004 FSU CIS 5930 Internet Protocols 1

Traffic control and Quality of Service

Reading: Chapter 18

Fall 2004 FSU CIS 5930 Internet Protocols 2

Some basic concepts• Traffic policing

– Incompliant packets dropped

• Traffic shaping– Incompliant packets held till satisfied

• Queueing discipline– Packet departure order (time)

• Classes– Packet holders

• Filters– Packet classifiers

Fall 2004 FSU CIS 5930 Internet Protocols 3

Traffic control in Linux kernel

..........

dev.cdev.c

dev.cdev.c

driver.cdriver.c

net_interrupt

netif_rx

net_rx_action

Scheduler

do_softirq

br_input.cbr_input.c

handle_bridgeCONFIG_BRIDGE

dev_alloc_skb()

eth_type_trans()

CPU1 CPU2

softnet_data[cpun].input_pkt_queue

Dat

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k la

yer

(OS

I-La

yer

1+2)

arp_rcv ip_rcv p8022_rcv

Laye

r 3

dev.cdev.c

dev_queue_xmit

dev->qdisc->enqueue

dev.cdev.c

driver.cdriver.c

dev->hard_start_xmit

qdisc_run

qdisc_restart

dev->qdisc->dequeue

Scheduler

eth0 eth1

ip_queue_xmitarp_send

...

net_tx_action

ETH_P_802_2

Fall 2004 FSU CIS 5930 Internet Protocols 4

Traffic control

dev.c, net/sched/*dev.c, net/sched/*

softirq.c, netdevice.hsoftirq.c, netdevice.h

dev->qdisc->enqueue

driver.cdriver.c

dev->hard_start_xmit

qdisc_run

qdisc_restart dev->qdisc->dequeue

Scheduler

net_tx_action

dev_queue_xmit

timer_handler netif_scheduleTimer

cpu_raise_softirq

do_softirq

NET_TX_SOFTIRQ

One specificqueueing discipline

enqueue dequeue

Fall 2004 FSU CIS 5930 Internet Protocols 5

Basic queue discipline interface

• enqueue()– Put a packet into queue

• dequeue()– Get a packet from the queue

• drop()– Remove a packet

• requeue(), reset(), init(), destroy(), change(), dump()

Fall 2004 FSU CIS 5930 Internet Protocols 6

struct Qdisc

Struct Qdisc {int (*enqueue)(…);struct sk_buff (*dequeue)(…);struct Qdisc_ops *ops;struct Qdisc *next;struct sk_buff_head q;struct net_device *dev;…

}

Fall 2004 FSU CIS 5930 Internet Protocols 7

Adding a discipline into kernel

• pktsched_init()– Used when a discipline is compiled

permanently into kernel– Initializing RT-NETLINK interface– Calling register_qdisc() function

• register_qdisc()– Called by pktsched_init() or init_module()– Inserting discipline into the list– Allocating operations (functions)

Fall 2004 FSU CIS 5930 Internet Protocols 8

Filters

• classify()• init()• destroy()• delete()

Fall 2004 FSU CIS 5930 Internet Protocols 9

Implementing a discipline

• Concepts of token bucket filter– Rate R– Depth B

• Functions – tbf_init()– tbf_enqueue()– tbf_dequeue()