netdev - Re: [PATCH net-next] codel: add ce

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Date:	Sun, 10 May 2015 19:50:57 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, daniel@...earbox.net, fw@...len.de,
	glenn.judd@...ganstanley.com, nanditad@...gle.com,
	ncardwell@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH net-next] codel: add ce_threshold attribute

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 08 May 2015 15:05:12 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> For DCTCP or similar ECN based deployments on fabrics with shallow
> buffers, hosts are responsible for a good part of the buffering.
> 
> This patch adds an optional ce_threshold to codel & fq_codel qdiscs,
> so that DCTCP can have feedback from queuing in the host.
> 
> A DCTCP enabled egress port simply have a queue occupancy threshold
> above which ECT packets get CE mark.
> 
> In codel language this translates to a sojourn time, so that one doesn't
> have to worry about bytes or bandwidth but delays.
> 
> This makes the host an active participant in the health of the whole
> network.
> 
> This also helps experimenting DCTCP in a setup without DCTCP compliant
> fabric.
> 
> On following example, ce_threshold is set to 1ms, and we can see from
> 'ldelay xxx us' that TCP is not trying to go around the 5ms codel
> target.
> 
> Queue has more capacity to absorb inelastic bursts (say from UDP
> traffic), as queues are maintained to an optimal level.
 ...
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks a lot Eric.
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