netdev - Re: [PATCH 1/2] sch_netem: Remove classful functionality

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Message-ID: <49102C38.5070207@trash.net>
Date:	Tue, 04 Nov 2008 12:04:24 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	Jarek Poplawski <jarkao2@...il.com>,
	David Miller <davem@...emloft.net>,
	herbert@...dor.apana.org.au, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] sch_netem: Remove classful functionality

Stephen Hemminger wrote:
> On Mon, 03 Nov 2008 12:20:25 +0100
> Patrick McHardy <kaber@...sh.net> wrote:
> 
>> Whats wrong with simply using TBF as parent qdisc of netem?
> 
> It works but does something slightly different.
> 
>    netem inside TBF is like long delay network followed by choke on last hop
>    TBF inside netem was like choke on uplink followed by long delay network.

The behaviour visible on either side is identical though.

TBF only affects the ->dequeue path, in which netem only handles delays.
In both cases the total delay is the maximum of the absolute delay
imposed by netem + the delay resulting from rate-limiting (the maximum
because TBF can recharge while netem is delaying). Both values are
independant from each other, so the maximum is always the same.
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