NETEM - fq_codel and pfifo_fast change/add tc rule Post: 303039021

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Contact Us Post Here to Contact Site Administrators and Moderators How to Post in the The UNIX and Linux Forums NETEM - fq_codel and pfifo_fast change/add tc rule Post 303039021 by Neo on Thursday 19th of September 2019 11:05:17 PM

09-20-2019

Administrator

As as recall, the netem package has issues related to granularity; and when I did a quick look, I found this in the man page:

Quote:

The main known limitation of Netem are related to timer granularity, since Linux is not a real-time operating system.

This could be way off base, but perhaps using a 0.5% loss parameter is too granular for Linux?

Did you experiment using a larger parameter, such as 5% or even 2% first, to test?

Sorry if this is not helpful or I'm way off the mark.

EDIT: Yes, I am way off the mark... I just read this in the docs on Packet Loss:

Ref: https://wiki.linuxfoundation.org/net...em#packet_loss

Code:

Packet loss
 
Random packet loss is specified in the 'tc' command in percent. The smallest possible non-zero value is:

232 = 0.0000000232%

 # tc qdisc change dev eth0 root netem loss 0.1%
This causes 1/10th of a percent (i.e 1 out of 1000) packets to be randomly dropped.

An optional correlation may also be added. This causes the random number generator to be less random and can be used to emulate packet burst losses.

 # tc qdisc change dev eth0 root netem loss 0.3% 25%
This will cause 0.3% of packets to be lost, and each successive probability depends by a quarter on the last one.

Probn = .25 * Probn-1 + .75 * Random

I'm really interested in this topic, so looking forward to any updates. What version of Linux are you using? I may install netem on Ubuntu and check it out.

Thanks.

Neo

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tc-bfifo

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).  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.

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)