| .TH PBFIFO 8 "10 January 2002" "iproute2" "Linux" |
| .SH NAME |
| pfifo \- Packet limited First In, First Out queue |
| .P |
| bfifo \- Byte limited First In, First Out queue |
| |
| .SH SYNOPSIS |
| .B tc qdisc ... add pfifo |
| .B [ limit |
| packets |
| .B ] |
| .P |
| .B tc qdisc ... add bfifo |
| .B [ limit |
| bytes |
| .B ] |
| |
| .SH DESCRIPTION |
| The pfifo and bfifo qdiscs are unadorned First In, First Out queues. They are the |
| simplest queues possible and therefore have no overhead. |
| .B pfifo |
| constrains the queue size as measured in packets. |
| .B 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. |
| |
| .SH 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'. |
| |
| .SH PARAMETERS |
| .TP |
| limit |
| Maximum queue size. Specified in bytes for bfifo, in packets for pfifo. For pfifo, defaults |
| to the interface txqueuelen, as specified with |
| .BR ifconfig (8) |
| or |
| .BR ip (8). |
| The range for this parameter is [0, UINT32_MAX]. |
| |
| For bfifo, it defaults to the txqueuelen multiplied by the interface MTU. |
| The range for this parameter is [0, UINT32_MAX] bytes. |
| |
| Note: The link layer header was considered when counting packets length. |
| |
| .SH OUTPUT |
| The output of |
| .B 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: |
| .P |
| .nf |
| # tc -s qdisc ls dev eth0 |
| qdisc pfifo 8001: dev eth0 limit 100p |
| Sent 45894 bytes 681 pkts (dropped 0, overlimits 0) |
| .fi |
| |
| If a backlog occurs, this is displayed as well. |
| .SH SEE ALSO |
| .BR tc (8) |
| |
| .SH AUTHORS |
| Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru> |
| |
| This manpage maintained by bert hubert <ahu@ds9a.nl> |