中文介绍可以看这篇Linux TC：一个能控制发送端流量的工具，模拟网络异常的原理介绍
看了中文，再看英文man tc，原来如此，英文的措辞更清晰，且不断更新。
SYNOPSIS命令格式
tc [ OPTIONS ] qdisc [ add | change | replace | link | delete ] dev DEV [ parent qdisc-id | root ] [ handle qdisc-id ] qdisc [qdisc specific parameters ]
tc [ OPTIONS ] class [ add | change | replace | delete ] dev DEV parent qdisc-id [ classid class-id ] qdisc [ qdisc specific parameters ]
tc [ OPTIONS ] filter [ add | change | replace | delete ] dev DEV [ parent qdisc-id | root ] protocol protocol prio priority filtertype [ filtertype specific parameters ] flowid flow-id
tc [ OPTIONS ] [ FORMAT ] qdisc show [ dev DEV ]
tc [ OPTIONS ] [ FORMAT ] class show dev DEV
tc [ OPTIONS ] filter show dev DEV
DESCRIPTION描述
Tc is used to configure Traffic Control in the Linux kernel. Traffic Control consists of the following:
SHAPING：When traffic is shaped, its rate of transmission is under control. Shaping may be more than lowering the available bandwidth - it is also used to smooth out bursts in traffic for better network behaviour. Shaping occurs on egress.
SCHEDULING：By scheduling the transmission of packets it is possible to improve interactivity for traffic that needs it while still guaranteeing bandwidth to bulk transfers. Reordering is also called prioritizing, and happens only on egress.
POLICING：Whereas shaping deals with transmission of traffic, policing pertains to traffic arriving. Policing thus occurs on ingress.
DROPPING：Traffic exceeding a set bandwidth may also be dropped forthwith, both on ingress and on egress.
Processing of traffic is controlled by three kinds of objects: qdiscs, classes and filters.
QDISCS
qdisc is short for 'queueing discipline' and it is elementary to understanding traffic control. Whenever the kernel needs to send a packet to an interface, it is enqueued to the qdisc configured for that interface. Immediately afterwards, the kernel tries to get as many packets as possible from the qdisc, for giving them to the network adaptor driver.
A simple QDISC is the 'pfifo' one, which does no processing at all and is a pure First In, First Out queue. It does however store traffic when the network interface can't handle it momentarily.
CLASSES
Some qdiscs can contain classes, which contain further qdiscs - traffic may then be enqueued in any of the inner qdiscs, which are within the classes. When the kernel tries to dequeue a packet from such a classful qdisc it can come from any of the classes. A qdisc may for example prioritize certain kinds of traffic by trying to dequeue from certain classes before others.
FILTERS
A filter is used by a classful qdisc to determine in which class a packet will be enqueued. Whenever traffic arrives at a class with subclasses, it needs to be classified. Various methods may be employed to do so, one of these are the filters. All filters attached to the class are called, until one of them returns with a verdict. If no verdict was made, other criteria may be available. This differs per qdisc.
It is important to notice that filters reside within qdiscs - they are not masters of what happens.
The available filters are:
basic Filter packets based on an ematch expression. See tc-ematch(8) for details.
bpf Filter packets using (e)BPF, see tc-bpf(8) for details.
cgroup Filter packets based on the control group of their process. See tc-cgroup(8) for details.
flow, flower Flow-based classifiers, filtering packets based on their flow (identified by selectable keys). See tc-flow(8) and tc-flower(8) for details.
fw Filter based on fwmark. Directly maps fwmark value to traffic class. See tc-fw(8).
route Filter packets based on routing table. See tc-route(8) for details.
rsvp Match Resource Reservation Protocol (RSVP) packets.
tcindex Filter packets based on traffic control index. See tc-tcindex(8).
u32 Generic filtering on arbitrary packet data, assisted by syntax to abstract common operations. See tc-u32(8) for details.
matchall Traffic control filter that matches every packet. See tc-matchall(8) for details.
QEVENTS
Qdiscs may invoke user-configured actions when certain interesting events take place in the qdisc. Each qevent can either be unused, or can have a block attached to it. To this block are then attached filters using the "tc block BLOCK_IDX" syntax. The block is executed when the qevent associated with the attachment point takes place. For example, packet could be dropped, or delayed, etc., depending on the qdisc and the qevent in question.
For example: tc qdisc add dev eth0 root handle 1: red limit 500K avpkt 1K \ qevent early_drop block 10
tc filter add block 10 matchall action mirred egress mirror dev eth1
CLASSLESS QDISCS
The classless qdiscs are:
choke CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for unresponsive flows) is a classless qdisc designed to both identify and penalize flows that monopolize the queue. CHOKe is a variation of RED, and the configuration is similar to RED.
codel CoDel (pronounced "coddle") is an adaptive "no-knobs" active queue management algorithm (AQM) scheme that was developed to address the shortcomings of RED and its variants.
[p|b]fifo Simplest usable qdisc, pure First In, First Out behaviour.Limited in packets or in bytes.
fq Fair Queue Scheduler realises TCP pacing and scales to millions of concurrent flows per qdisc.
fq_codel Fair Queuing Controlled Delay is queuing discipline that combines Fair Queuing with the CoDel AQM scheme. FQ_Codel uses a stochastic model to classify incoming packets into different flows and is used to provide a fair share of the bandwidth to all the flows using the queue. Each such flow is managed by the CoDel queuing discipline. Reordering within a flow is avoided since Codel internally uses a FIFO queue.
fq_pie FQ-PIE (Flow Queuing with Proportional Integral controller Enhanced) is a queuing discipline that combines FlowQueuing with the PIE AQM scheme. FQ-PIE uses a Jenkins hash function to classify incoming packets into different flows and is used to provide a fair share of the bandwidth to all the flows using the qdisc. Each such flow is managed by the PIE algorithm.
gred Generalized Random Early Detection combines multiple RED queues in order to achieve multiple drop priorities. This is required to realize Assured Forwarding (RFC 2597).
hhf Heavy-Hitter Filter differentiates between small flows and the opposite, heavy-hitters. The goal is to catch the heavy-hitters and move them to a separate queue with less priority so that bulk traffic does not affect the latency of critical traffic.
ingress This is a special qdisc as it applies to incoming traffic on an interface, allowing for it to be filtered and policed.
mqprio The Multiqueue Priority Qdisc is a simple queuing discipline that allows mapping traffic flows to hardware queue ranges using priorities and a configurable priorit to traffic class mapping. A traffic class in this context is a set of contiguous qdisc classes which map 1:1 to a set of hardware exposed queues.
multiq Multiqueue is a qdisc optimized for devices with multiple Tx queues. It has been added for hardware that wishes to avoid head-of-line blocking. It will cycle though the bands and verify that the hardware queue associated with the band is not stopped prior to dequeuing a packet.
netem Network Emulator is an enhancement of the Linux traffic control facilities that allow to add delay, packet loss, duplication and more other characteristics to packets outgoing from a selected network interface.
pfifo_fast Standard qdisc for 'Advanced Router' enabled kernels. Consists of a three-band queue which honors Type of Service flags, as well as the priority that may be assigned to a packet.
pie Proportional Integral controller-Enhanced (PIE) is a control theoretic active queue management scheme. It is based on the proportional integral controller but aims to control delay.
red Random Early Detection simulates physical congestion by randomly dropping packets when nearing configured bandwidth allocation. Well suited to very large bandwidth applications.
rr Round-Robin qdisc with support for multiqueue network devices. Removed from Linux since kernel version 2.6.27.
sfb Stochastic Fair Blue is a classless qdisc to manage congestion based on packet loss and link utilization history while trying to prevent non-responsive flows (i.e. flows that do not react to congestion marking or dropped packets) from impacting performance of responsive flows. Unlike RED, where the marking probability has to be configured, BLUE tries to determine the ideal marking probability automatically.
sfq Stochastic Fairness Queueing reorders queued traffic so each 'session' gets to send a packet in turn.
tbf The Token Bucket Filter is suited for slowing traffic down to a precisely configured rate. Scales well to large bandwidths.
CLASSFUL QDISCS
The classful qdiscs are:
ATM Map flows to virtual circuits of an underlying asynchronous transfer mode device.
CBQ Class Based Queueing implements a rich linksharing hierarchy of classes. It contains shaping elements as well as prioritizing capabilities. Shaping is performed using link idle time calculations based on average packet size and underlying link bandwidth. The latter may be ill-defined for some interfaces.
DRR The Deficit Round Robin Scheduler is a more flexible replacement for Stochastic Fairness Queuing. Unlike SFQ, there are no built-in queues -- you need to add classes and then set up filters to classify packets accordingly. This can be useful e.g. for using RED qdiscs with different settings for particular traffic. There is no default class -- if a packet cannot be classified, it is dropped.
DSMARK Classify packets based on TOS field, change TOS field of packets based on classification.
ETS The ETS qdisc is a queuing discipline that merges functionality of PRIO and DRR qdiscs in one scheduler. ETS makes it easy to configure a set of strict and bandwidth-sharing bands to implement the transmission selection described in 802.1Qaz.
HFSC Hierarchical Fair Service Curve guarantees precise bandwidth and delay allocation for leaf classes and allocates excess bandwidth fairly. Unlike HTB, it makes use of packet dropping to achieve low delays which interactive sessions benefit from.
HTB The Hierarchy Token Bucket implements a rich linksharing hierarchy of classes with an emphasis on conforming toexisting practices. HTB facilitates guaranteeing bandwidth to classes, while also allowing specification of upper limits to inter-class sharing. It contains shaping elements, based on TBF and can prioritize classes.
PRIO The PRIO qdisc is a non-shaping container for a configurable number of classes which are dequeued in order. This allows for easy prioritization of traffic,where lower classes are only able to send if higher ones have no packets available. To facilitate configuration,Type Of Service bits are honored by default.
QFQ Quick Fair Queueing is an O(1) scheduler that provides near-optimal guarantees, and is the first to achieve that goal with a constant cost also with respect to the number of groups and the packet length. The QFQ algorithm has no loops, and uses very simple instructions and data structures that lend themselves very well to a hardware implementation.
THEORY OF OPERATION操作原理
Classes form a tree, where each class has a single parent. A class may have multiple children. Some qdiscs allow for runtime addition of classes (CBQ, HTB) while others (PRIO) are created with a static number of children.
Qdiscs which allow dynamic addition of classes can have zero or more subclasses to which traffic may be enqueued.
Furthermore, each class contains a leaf qdisc which by default has pfifo behaviour, although another qdisc can be attached in place. This qdisc may again contain classes, but each class can have only one leaf qdisc.
When a packet enters a classful qdisc it can be classified to one of the classes within. Three criteria are available,although not all qdiscs will use all three:
tc filters
If tc filters are attached to a class, they are consulted first for relevant instructions. Filters can match on all fields of a packet header, as well as on the firewall mark applied by ipchains or iptables.
Type of Service
Some qdiscs have built in rules for classifying packets based on the TOS field.
skb->priority
Userspace programs can encode a class-id in the 'skb->priority' field using the SO_PRIORITY option.
Each node within the tree can have its own filters but higher level filters may also point directly to lower classes.
If classification did not succeed, packets are enqueued to the leaf qdisc attached to that class. Check qdisc specific man‐pages for details, however.
AUTHOR
Manpage maintained by bert hubert (ahu@ds9a.nl)
COLOPHON
This page is part of the iproute2 (utilities for controlling TCP/IP networking and traffic) project. Information about the project can be found at ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
If you have a bug report for this manual page, send it to netdev@vger.kernel.org, shemminger@osdl.org. This page was obtained from the project's upstream Git repository ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on 2021-08-27. (At that time, the date of the most recent commit that was found in the repository was 2021-08-18.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which is not part of the original manual page), send a mail to man-pages@man7.org
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