New Developments in Link Emulation and packet Scheduling in FreeBSD, Linux, and Windows

Posted in Companies, Networking, Conferences on July 11, 2012

Google Tech Talk
March 29, 2010


Presented by Luigi Rizzo.

In this talk we will give an overview of some recent activity done at the Universita` di Pisa on link emulation and packet scheduling. We will cover two main topics:

- the "dummynet" link emulator shaper at
which has been recently ported to Linux and Windows (in addition to FreeBSD and OSX), and extended with support for multiple scheduling algorithms. In the talk we will briefly the features of dummynet, discuss its performance and applicability, and describe the strategy used to build kernel modules for three very different systems starting from the same codebase.

- fast packet scheduling algorithms.

We will present QFQ, a truly practical WFQ scheduler with O(1) complexity and very small constants (110ns per packet on a low-end workstation, 2.5..4 times faster than the best competitor). QFQ is available on all major platforms as part of dummynet.

The talk will briefly cover the features of QFQ, and compare it with other existing packet scheduling algorithms. (joint work with Paolo Valente and Fabio Checconi).

Luigi Rizzo is an associate Professor at the Universita` di Pisa, and a long time FreeBSD and Asterisk developer. He has worked on various networking topics including multicast congestion control, emulation, and operating system support for high performance networking.

In addition to the work presented here, Luigi and his colleagues are currently working on disk scheduling, and will be glad to discuss the topic with people interested. A description of this work is at

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