netdev - Re: [PATCH 2/2] net: netem: always adjust now/delay when not reordering

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Message-ID: <20130821103507.3a499488@samsung-9>
Date:	Wed, 21 Aug 2013 10:35:07 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ferry Huberts <mailings@...ie.com>, Johannes Naab <jn@...sta.de>,
	netdev@...r.kernel.org, hagen@...u.net
Subject: Re: [PATCH 2/2] net: netem: always adjust now/delay when not
 reordering

On Wed, 21 Aug 2013 10:00:17 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

> On Wed, 2013-08-21 at 18:14 +0200, Ferry Huberts wrote:
> 
> > Well no. We expected no reordering because reordering is not enabled.
> 
> 
> Sending packets with random delays happening in the 'network' _will_
> reorder packets at the receiver.
> 
> The 'reorder' netem attribute is quite limited and not practical,
> because it only queues the packet at the head of the queue instead of
> tail. This is not what happens on the networks.
> 
> You want something very special, and this needs a new parameter to netem
> qdisc, or a new qdisc.
> 
> If I setup "netem rate 1Mbit delay 1000ms 50ms", and send a burst of 100
> small packets, I expect these _all_ packets reach the destination in
> less than 1050ms.
> 
> I do not want packet1 being delivered at t0+1020ms,
> packet2 being delivered at t0+1020+1030ms
> packet100 being delivered at t0+1020+1030++...+ = t0+~100sec
> 
> If your patch solves the problem, good, but I see no clear test of this.

The current behavior followed what NISTnet did. At the time, I wanted
NISTnet users to be able to use netem without a lot of surprises.
  http://www-x.antd.nist.gov/nistnet/


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