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

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Date:	Mon, 3 Jan 2011 09:58:42 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	hadi@...erus.ca, Jarek Poplawski <jarkao2@...il.com>,
	David Miller <davem@...emloft.net>,
	Jesper Dangaard Brouer <hawk@...u.dk>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] net_sched: mark packet staying on queue too long

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.
> 
> 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 ?
> 
> The idea is to take into account the time packet stayed in the queue,
> regardless of other class parameters.
> 
> Following quick and dirty patch to show the idea. Of course, the delay
> should be configured on each SFQ/RED/XXXX class, so it would need an
> iproute2 patch, and the delay unit should be "ms" (or even "us"), not
> ticks, but as I said this is a quick and dirty patch (net-next-2.6
> based)
> 
> Using jiffies allows only delays above 3 or 4 ticks...
> 
> Or maybe ECN is just a dream :(

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


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