pfifo_fast(8) [suse man page]
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 config- ured qdisc. SEE ALSO
tc(8) AUTHORS
Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru> This manpage maintained by bert hubert <ahu@ds9a.nl> iproute2 10 January 2002 PFIFO_FAST(8)
Check Out this Related Man Page
PBFIFO(8) Linux PBFIFO(8) NAME
pfifo - Packet limited First In, First Out queue bfifo - Byte limited First In, First Out queue SYNOPSIS
tc qdisc ... add pfifo [ limit packets ] tc qdisc ... add bfifo [ limit bytes ] DESCRIPTION
The pfifo and bfifo qdiscs are unadorned First In, First Out queues. They are the simplest queues possible and therefore have no overhead. pfifo constrains the queue size as measured in packets. bfifo does so as measured in bytes. Like all non-default qdiscs, they maintain statistics. This might be a reason to prefer pfifo or bfifo over the default. ALGORITHM
A list of packets is maintained, when a packet is enqueued it gets inserted at the tail of a list. When a packet needs to be sent out to the network, it is taken from the head of the list. If the list is too long, no further packets are allowed on. This is called 'tail drop'. PARAMETERS
limit Maximum queue size. Specified in bytes for bfifo, in packets for pfifo. For pfifo, defaults to the interface txqueuelen, as speci- fied with ifconfig(8) or ip(8). For bfifo, it defaults to the txqueuelen multiplied by the interface MTU. OUTPUT
The output of tc -s qdisc ls contains the limit, either in packets or in bytes, and the number of bytes and packets actually sent. An unsent and dropped packet only appears between braces and is not counted as 'Sent'. In this example, the queue length is 100 packets, 45894 bytes were sent over 681 packets. No packets were dropped, and as the pfifo queue does not slow down packets, there were also no overlimits: # tc -s qdisc ls dev eth0 qdisc pfifo 8001: dev eth0 limit 100p Sent 45894 bytes 681 pkts (dropped 0, overlimits 0) If a backlog occurs, this is displayed as well. SEE ALSO
tc(8) AUTHORS
Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru> This manpage maintained by bert hubert <ahu@ds9a.nl> iproute2 10 January 2002 PBFIFO(8)