[Bloat] About Stochastic Fair Blue (SFB)

Dave Täht d at taht.net
Fri Feb 4 07:12:53 PST 2011

Juliusz Chroboczek <jch at pps.jussieu.fr> writes:

> Hi again,

> One AQM that attempts both is Stochastic Fair a stochastically-fair
> variant of BLUE [1].  In addition to reducing buffer size and enforcing
> rough inter-flow fairness, SFB will reliably detect unresponsive flows
> and rate-limit them.
> In order to experiment with SFB, I've implemented it for Linux a couple
> of years ago [2].  Unfortunately, I've given up for now on trying to get
> it into the mainline kernel, and I'm not sure I want to try again [3].

I had incorporated juliusz's patches to the tc utility here in my git
repo here a few weeks back.


(I would be very interested in accumulating the other patches to tc for
the other new AQMs, too, if anyone knows what or where they are)

So a patched tc + SFB modules gives you a new AQM to work with.

The SFB code seems to compile as modules and insert into modern kernels
just fine. I've built it on arm, x86_64, and x86, with mips on my list

However, the usage is a little vague. Could you make some suggestions as
to a "shaping stack" to fiddle with, for example, a wireless environment
or home gateway scenario? [1]

Also, would you mind if I also put the SFB code into git somewhere 
on github? It could use a few minor tweaks (make install). 

Things I like about SFB

1) You can hash against multiple combinations of things. For example, in
the home gateway scenario, you could hash against IP addresses only, not
IP/port numbers - to give a per-device level of fairness. 

2) It has a brilliant idea in the bloom filter - it looks like that
concept can scale..

3) It does packet marking... (So has to be used in combination with
something else)

4) it works with ipv6.

Things that I don't "get" about SFB.

1) I don't understand how the penalty box concept works.

2) I don't understand how it would interact with shaping above and below it[2]

Dave Taht

[1] and in my case my driver set is so bloated that traffic shaping at
the moment does little good - but I'm getting there.

[2] Yes, I've read the paper. And the code. Twice.

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