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

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Date:	Sat, 09 May 2015 23:21:35 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
CC:	netdev <netdev@...r.kernel.org>, Florian Westphal <fw@...len.de>,
	Glenn Judd <glenn.judd@...ganstanley.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next] codel: add ce_threshold attribute

On 05/09/2015 12:05 AM, Eric Dumazet wrote:
> 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.
>
> lpaa23:~# ./tc -s -d qd sh dev eth1
> qdisc mq 1: dev eth1 root
>   Sent 87910654696 bytes 58065331 pkt (dropped 0, overlimits 0 requeues 42961)
>   backlog 3108242b 364p requeues 42961
> qdisc codel 8063: dev eth1 parent 1:1 limit 1000p target 5.0ms ce_threshold 1.0ms interval 100.0ms
>   Sent 7363778701 bytes 4863809 pkt (dropped 0, overlimits 0 requeues 5503)
>   rate 2348Mbit 193919pps backlog 255866b 46p requeues 5503
>    count 0 lastcount 0 ldelay 1.0ms drop_next 0us
>    maxpacket 68130 ecn_mark 0 drop_overlimit 0 ce_mark 72384
> qdisc codel 8064: dev eth1 parent 1:2 limit 1000p target 5.0ms ce_threshold 1.0ms interval 100.0ms
>   Sent 7636486190 bytes 5043942 pkt (dropped 0, overlimits 0 requeues 5186)
>   rate 2319Mbit 191538pps backlog 207418b 64p requeues 5186
>    count 0 lastcount 0 ldelay 694us drop_next 0us
>    maxpacket 68130 ecn_mark 0 drop_overlimit 0 ce_mark 69873
> qdisc codel 8065: dev eth1 parent 1:3 limit 1000p target 5.0ms ce_threshold 1.0ms interval 100.0ms
>   Sent 11569360142 bytes 7641602 pkt (dropped 0, overlimits 0 requeues 5554)
>   rate 3041Mbit 251096pps backlog 210446b 59p requeues 5554
>    count 0 lastcount 0 ldelay 889us drop_next 0us
>    maxpacket 68130 ecn_mark 0 drop_overlimit 0 ce_mark 37780
> ...
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Florian Westphal <fw@...len.de>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Glenn Judd <glenn.judd@...ganstanley.com>
> Cc: Nandita Dukkipati <nanditad@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Cc: Yuchung Cheng <ycheng@...gle.com>

Great work Eric, this looks very useful!
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