netdev - Re: [PATCH net-next] fq_codel: Fair Queue Codel AQM

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Date:	Fri, 11 May 2012 23:03:10 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Dave Taht <dave.taht@...ferbloat.net>,
	Kathleen Nichols <nichols@...lere.com>,
	Van Jacobson <van@...lere.net>,
	Tom Herbert <therbert@...gle.com>,
	Matt Mathis <mattmathis@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH net-next] fq_codel: Fair Queue Codel AQM

On Fri, May 11, 2012 at 9:59 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> Fair Queue Codel implementation.
>
> Principles :
>
> - Packets are classified (internal classifier or external) on flows.
> - This is a Stochastic model (as we use a hash, several flows might
>                              be hashed on same slot)
> - Each flow has a CoDel managed queue.
> - Flows are linked onto two (Round Robin) lists,
>  so that new flows have priority on old ones.

I don't think it is a good idea, as the old ones may be starved. It isn't
fair. Why not use the conventional DRR?

> +
> +       /* Queue is full! Find the fat flow and drop packet from it.
> +        * This might sound expensive, but with 1024 flows, we scan
> +        * 4KB of memory, and we dont need to handle a complex tree
> +        * in fast path (packet queue/enqueue) with many cache misses.
> +        */

How about the tricks used by SFQ?

Thanks.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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