Re: [Bloat] About Stochastic Fair Blue (SFB)

[Jim Gettys <jg@freedesktop.org>]

On 02/04/2011 04:46 AM, Juliusz Chroboczek wrote:
> Hi again,
>
> In his series of articles, Jim has concentrated on router-based
> solutions to delay issues.  He mentioned AQM policies in routers, and
> notably the venerable RED.

Referred to hereafter as RED 93.

For those of you who have not waded through all the postings, RED is 
often all that has been available in most Internet routers, and RED 93 
won't handle the common case we face most commonly, which is 802.11.
(This is the opinion of Van Jacobson, who with Sally Floyd invented RED 93).

The reasons for this is that RED 93 can't handle the highly variable 
"goodput" we see in wireless networks  (and some other systems) due to 
its static configuration, and Van says it's stability given the volatile 
traffic mix we have in these networks also makes RED 93 hopeless.

I just want to make clear we face a problem here we can't solve with RED 93.

We have to explore our alternatives in detail.

>
> AQMs are designed to achieve two different (but not necessarily
> contradictory) goals: to improve the behaviour of the traffic (notably
> by reducing the amount of buffering, which is what we're concerned about
> here), and to improve fairness.  For example, RED is mostly concerned
> with the former, while CHOKe is only concerned with the latter.

If we don't manage these insane buffers, we've lost.

>
> 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].
>
> --Juliusz
>
> [1] W. Feng, D. Kandlur, D. Saha, K. Shin. Blue: A New Class of Active
>      Queue Management Algorithms. U. Michigan CSE-TR-387-99, April 1999.
>      http://www.thefengs.com/wuchang/blue/CSE-TR-387-99.pdf
> [2] http://www.pps.jussieu.fr/~jch/software/sfb/
> [3] http://article.gmane.org/gmane.linux.network/183813

Juliusz,  have you thought about the host case at all?  One of the 
places we're getting insane buffering is in the operating systems 
themselves (e.g. the experiment I did with a 100Mbps switch). My 
intuition is that we have to do AQM in hosts, not just routers.
		- Jim