PFIFO_FAST(8) Linux PFIFO_FAST(8)
NAME
pfifo_fast - three-band first in, first out queue
DESCRIPTION
pfifo_fast is the default qdisc of each interface.
Whenever an interface is created, the pfifo_fast qdisc is automatically used as a queue. If another qdisc is
attached, it preempts the default pfifo_fast, which automatically returns to function when an existing qdisc
is detached.
In this sense this qdisc is magic, and unlike other qdiscs.
ALGORITHM
The algorithm is very similar to that of the classful tc-prio(8) qdisc. pfifo_fast is like three tc-pfifo(8)
queues side by side, where packets can be enqueued in any of the three bands based on their Type of Service
bits or assigned priority.
Not all three bands are dequeued simultaneously - as long as lower bands have traffic, higher bands are never
dequeued. This can be used to prioritize interactive traffic or penalize 'lowest cost' traffic.
Each band can be txqueuelen packets long, as configured with ifconfig(8) or ip(8). Additional packets coming
in are not enqueued but are instead dropped.
See tc-prio(8) for complete details on how TOS bits are translated into bands.
PARAMETERS
txqueuelen
The length of the three bands depends on the interface txqueuelen, as specified with ifconfig(8) or
ip(8).
BUGS
Does not maintain statistics and does not show up in tc qdisc ls. This is because it is the automatic default
in the absence of a configured qdisc.
SEE ALSO
tc(8)
AUTHORS
Alexey N. Kuznetsov, <[email protected]>
This manpage maintained by bert hubert <[email protected]>
iproute2 10 January 2002 PFIFO_FAST(8)
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