+++ /dev/null
-.TH PRIO 8 "16 December 2001" "iproute2" "Linux"
-.SH NAME
-PRIO \- Priority qdisc
-.SH SYNOPSIS
-.B tc qdisc ... dev
-dev
-.B ( parent
-classid
-.B | root) [ handle
-major:
-.B ] prio [ bands
-bands
-.B ] [ priomap
-band,band,band...
-.B ] [ estimator
-interval timeconstant
-.B ]
-
-.SH DESCRIPTION
-The PRIO qdisc is a simple classful queueing discipline that contains
-an arbitrary number of classes of differing priority. The classes are
-dequeued in numerical descending order of priority. PRIO is a scheduler
-and never delays packets - it is a work-conserving qdisc, though the qdiscs
-contained in the classes may not be.
-
-Very useful for lowering latency when there is no need for slowing down
-traffic.
-
-.SH ALGORITHM
-On creation with 'tc qdisc add', a fixed number of bands is created. Each
-band is a class, although is not possible to add classes with 'tc qdisc
-add', the number of bands to be created must instead be specified on the
-commandline attaching PRIO to its root.
-
-When dequeueing, band 0 is tried first and only if it did not deliver a
-packet does PRIO try band 1, and so onwards. Maximum reliability packets
-should therefore go to band 0, minimum delay to band 1 and the rest to band
-2.
-
-As the PRIO qdisc itself will have minor number 0, band 0 is actually
-major:1, band 1 is major:2, etc. For major, substitute the major number
-assigned to the qdisc on 'tc qdisc add' with the
-.B handle
-parameter.
-
-.SH CLASSIFICATION
-Three methods are available to PRIO to determine in which band a packet will
-be enqueued.
-.TP
-From userspace
-A process with sufficient privileges can encode the destination class
-directly with SO_PRIORITY, see
-.BR tc(7).
-.TP
-with a tc filter
-A tc filter attached to the root qdisc can point traffic directly to a class
-.TP
-with the priomap
-Based on the packet priority, which in turn is derived from the Type of
-Service assigned to the packet.
-.P
-Only the priomap is specific to this qdisc.
-.SH QDISC PARAMETERS
-.TP
-bands
-Number of bands. If changed from the default of 3,
-.B priomap
-must be updated as well.
-.TP
-priomap
-The priomap maps the priority of
-a packet to a class. The priority can either be set directly from userspace,
-or be derived from the Type of Service of the packet.
-
-Determines how packet priorities, as assigned by the kernel, map to
-bands. Mapping occurs based on the TOS octet of the packet, which looks like
-this:
-
-.nf
-0 1 2 3 4 5 6 7
-+---+---+---+---+---+---+---+---+
-| | | |
-|PRECEDENCE | TOS |MBZ|
-| | | |
-+---+---+---+---+---+---+---+---+
-.fi
-
-The four TOS bits (the 'TOS field') are defined as:
-
-.nf
-Binary Decimcal Meaning
------------------------------------------
-1000 8 Minimize delay (md)
-0100 4 Maximize throughput (mt)
-0010 2 Maximize reliability (mr)
-0001 1 Minimize monetary cost (mmc)
-0000 0 Normal Service
-.fi
-
-As there is 1 bit to the right of these four bits, the actual value of the
-TOS field is double the value of the TOS bits. Tcpdump -v -v shows you the
-value of the entire TOS field, not just the four bits. It is the value you
-see in the first column of this table:
-
-.nf
-TOS Bits Means Linux Priority Band
-------------------------------------------------------------
-0x0 0 Normal Service 0 Best Effort 1
-0x2 1 Minimize Monetary Cost 1 Filler 2
-0x4 2 Maximize Reliability 0 Best Effort 1
-0x6 3 mmc+mr 0 Best Effort 1
-0x8 4 Maximize Throughput 2 Bulk 2
-0xa 5 mmc+mt 2 Bulk 2
-0xc 6 mr+mt 2 Bulk 2
-0xe 7 mmc+mr+mt 2 Bulk 2
-0x10 8 Minimize Delay 6 Interactive 0
-0x12 9 mmc+md 6 Interactive 0
-0x14 10 mr+md 6 Interactive 0
-0x16 11 mmc+mr+md 6 Interactive 0
-0x18 12 mt+md 4 Int. Bulk 1
-0x1a 13 mmc+mt+md 4 Int. Bulk 1
-0x1c 14 mr+mt+md 4 Int. Bulk 1
-0x1e 15 mmc+mr+mt+md 4 Int. Bulk 1
-.fi
-
-The second column contains the value of the relevant
-four TOS bits, followed by their translated meaning. For example, 15 stands
-for a packet wanting Minimal Montetary Cost, Maximum Reliability, Maximum
-Throughput AND Minimum Delay.
-
-The fourth column lists the way the Linux kernel interprets the TOS bits, by
-showing to which Priority they are mapped.
-
-The last column shows the result of the default priomap. On the commandline,
-the default priomap looks like this:
-
- 1, 2, 2, 2, 1, 2, 0, 0 , 1, 1, 1, 1, 1, 1, 1, 1
-
-This means that priority 4, for example, gets mapped to band number 1.
-The priomap also allows you to list higher priorities (> 7) which do not
-correspond to TOS mappings, but which are set by other means.
-
-This table from RFC 1349 (read it for more details) explains how
-applications might very well set their TOS bits:
-
-.nf
-TELNET 1000 (minimize delay)
-FTP
- Control 1000 (minimize delay)
- Data 0100 (maximize throughput)
-
-TFTP 1000 (minimize delay)
-
-SMTP
- Command phase 1000 (minimize delay)
- DATA phase 0100 (maximize throughput)
-
-Domain Name Service
- UDP Query 1000 (minimize delay)
- TCP Query 0000
- Zone Transfer 0100 (maximize throughput)
-
-NNTP 0001 (minimize monetary cost)
-
-ICMP
- Errors 0000
- Requests 0000 (mostly)
- Responses <same as request> (mostly)
-.fi
-
-
-.SH CLASSES
-PRIO classes cannot be configured further - they are automatically created
-when the PRIO qdisc is attached. Each class however can contain yet a
-further qdisc.
-
-.SH BUGS
-Large amounts of traffic in the lower bands can cause starvation of higher
-bands. Can be prevented by attaching a shaper (for example,
-.BR tc-tbf(8)
-to these bands to make sure they cannot dominate the link.
-
-.SH AUTHORS
-Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>, J Hadi Salim
-<hadi@cyberus.ca>. This manpage maintained by bert hubert <ahu@ds9a.nl>
-
-
git://git.onelab.eu / iproute2.git / blobdiff