- PIE_MAX_PROB is compared to variable of int64_t and the type promotion
rules can cause the value of that variable to be treated as unsigned.
If the value is actually negative, then the result of the comparsion
is incorrect, causing the algorithm to perform poorly in some
situations. Changing the constant to be signed cause the comparision
to work correctly.
- PIE_SCALE is also compared to signed values. Fortunately they are
also compared to zero and negative values are discarded so this is
more of a cosmetic fix.
- PIE_DQ_THRESHOLD is only compared to unsigned values, but it is small
enough that the automatic promotion to unsigned is harmless.
Submitted by: Rasool Al-Saadi <ralsaadi@swin.edu.au>
MFC after: 1 week
fractional floating point values with integer divides. This will
eliminate any chance that the compiler will generate code to evaluate
the expression using floating point at runtime.
Suggested by: bde
Submitted by: Rasool Al-Saadi <ralsaadi@swin.edu.au>
MFC after: 8 days (with r300779 and r300949)
Centre for Advanced Internet Architectures
Implementing AQM in FreeBSD
* Overview <http://caia.swin.edu.au/freebsd/aqm/index.html>
* Articles, Papers and Presentations
<http://caia.swin.edu.au/freebsd/aqm/papers.html>
* Patches and Tools <http://caia.swin.edu.au/freebsd/aqm/downloads.html>
Overview
Recent years have seen a resurgence of interest in better managing
the depth of bottleneck queues in routers, switches and other places
that get congested. Solutions include transport protocol enhancements
at the end-hosts (such as delay-based or hybrid congestion control
schemes) and active queue management (AQM) schemes applied within
bottleneck queues.
The notion of AQM has been around since at least the late 1990s
(e.g. RFC 2309). In recent years the proliferation of oversized
buffers in all sorts of network devices (aka bufferbloat) has
stimulated keen community interest in four new AQM schemes -- CoDel,
FQ-CoDel, PIE and FQ-PIE.
The IETF AQM working group is looking to document these schemes,
and independent implementations are a corner-stone of the IETF's
process for confirming the clarity of publicly available protocol
descriptions. While significant development work on all three schemes
has occured in the Linux kernel, there is very little in FreeBSD.
Project Goals
This project began in late 2015, and aims to design and implement
functionally-correct versions of CoDel, FQ-CoDel, PIE and FQ_PIE
in FreeBSD (with code BSD-licensed as much as practical). We have
chosen to do this as extensions to FreeBSD's ipfw/dummynet firewall
and traffic shaper. Implementation of these AQM schemes in FreeBSD
will:
* Demonstrate whether the publicly available documentation is
sufficient to enable independent, functionally equivalent implementations
* Provide a broader suite of AQM options for sections the networking
community that rely on FreeBSD platforms
Program Members:
* Rasool Al Saadi (developer)
* Grenville Armitage (project lead)
Acknowledgements:
This project has been made possible in part by a gift from the
Comcast Innovation Fund.
Submitted by: Rasool Al-Saadi <ralsaadi@swin.edu.au>
X-No objection: core
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D6388
