netdev - Re: [RFC] net_sched: mark packet staying on queue too long

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Date:	Tue, 4 Jan 2011 15:19:26 +0100 (CET)
From:	Jesper Dangaard Brouer <hawk@...u.dk>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, hadi@...erus.ca,
	Jarek Poplawski <jarkao2@...il.com>,
	David Miller <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] net_sched: mark packet staying on queue too long

On Mon, 3 Jan 2011, Stephen Hemminger wrote:

> On Sun, 02 Jan 2011 22:27:11 +0100
> Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>> While playing with SFQ and other AQM, I was bothered to see how easy it
>> was for a single tcp flow to 'fill the pipe' and consume lot of memory
>> buffers in queues. I know Jesper use more than 50.000 SFQ on his
>> routers, and with GRO packets this can consume a lot of memory.

That is true, operations department went kind of crazy when they started 
to add/move customers to our new Nehalem Xeon 5550 systems.  I have 
stopped them now ;-)

The use of an SFQ per customer, actually also solves the buffer bloat 
issue for our customers...


>> I played a bit adding ECN in SFQ, first by marking packets for a
>> particular flow if this flow qlen was above a given threshold, and later
>> using another trick : ECN mark packet if it stayed longer than a given
>> delay in the queue. This of course could be done on other modules, what
>> do you think ?

This is very interesting stuff! :-)

Are you inspired by Jim Gettys buffer bloat discussions?

> ...
> You might want to look into CHOKe and ECSFQ which are other AQM models
> that have shown up in research.

Have you looked at the SFB (Stochastic Fair Blue) implementation by 
Juliusz Chroboczek?

http://www.pps.jussieu.fr/~jch/software/sfb/

Cheers,
   Jesper Brouer

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