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osdl.org!shemminger985794a2004-06-08 20:34:17 +00001.TH PFIFO_FAST 8 "10 January 2002" "iproute2" "Linux"
2.SH NAME
3pfifo_fast \- three-band first in, first out queue
4
5.SH DESCRIPTION
6pfifo_fast is the default qdisc of each interface.
7
8Whenever an interface is created, the pfifo_fast qdisc is automatically used
9as a queue. If another qdisc is attached, it preempts the default
10pfifo_fast, which automatically returns to function when an existing qdisc
11is detached.
12
13In this sense this qdisc is magic, and unlike other qdiscs.
14
15.SH ALGORITHM
Stephen Hemminger56992752015-11-23 15:41:37 -080016The algorithm is very similar to that of the classful
osdl.org!shemminger985794a2004-06-08 20:34:17 +000017.BR tc-prio (8)
Stephen Hemminger56992752015-11-23 15:41:37 -080018qdisc.
osdl.org!shemminger985794a2004-06-08 20:34:17 +000019.B pfifo_fast
20is like three
21.BR tc-pfifo (8)
22queues side by side, where packets can be enqueued in any of the three bands
Stephen Hemminger56992752015-11-23 15:41:37 -080023based on their Type of Service bits or assigned priority.
osdl.org!shemminger985794a2004-06-08 20:34:17 +000024
25Not all three bands are dequeued simultaneously - as long as lower bands
26have traffic, higher bands are never dequeued. This can be used to
27prioritize interactive traffic or penalize 'lowest cost' traffic.
28
29Each band can be txqueuelen packets long, as configured with
30.BR ifconfig (8)
Stephen Hemminger56992752015-11-23 15:41:37 -080031or
osdl.org!shemminger985794a2004-06-08 20:34:17 +000032.BR ip (8).
33Additional packets coming in are not enqueued but are instead dropped.
34
35See
36.BR tc-prio (8)
37for complete details on how TOS bits are translated into bands.
38.SH PARAMETERS
Stephen Hemminger56992752015-11-23 15:41:37 -080039.TP
osdl.org!shemminger985794a2004-06-08 20:34:17 +000040txqueuelen
41The length of the three bands depends on the interface txqueuelen, as
42specified with
43.BR ifconfig (8)
44or
45.BR ip (8).
46
47.SH BUGS
48Does not maintain statistics and does not show up in tc qdisc ls. This is because
Stephen Hemminger56992752015-11-23 15:41:37 -080049it is the automatic default in the absence of a configured qdisc.
osdl.org!shemminger985794a2004-06-08 20:34:17 +000050
51.SH SEE ALSO
52.BR tc (8)
53
54.SH AUTHORS
55Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>
56
57This manpage maintained by bert hubert <ahu@ds9a.nl>