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

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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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