From mboxrd@z Thu Jan  1 00:00:00 1970
From: Hagen Paul Pfeifer <hagen@jauu.net>
Subject: Re: [PATCH v3 net-next 2/2] netem: add cell concept to simulate  special MAC behavior
Date: Thu, 01 Dec 2011 10:36:56 +0100
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Cc: <netdev@vger.kernel.org>, Stephen Hemminger <shemminger@vyatta.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
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On Thu, 01 Dec 2011 10:01:48 +0100, Eric Dumazet wrote:



> Yes :)



damn!



> I want to be able to use netem on a 10Gigabit link, and simulate a 5ms

> delay. I already will hit the shared qdisc bottleneck, dont force me to

> use small packets !



No I don't want that. But with 10Gb/s links you will have packet

scheduling problems anyway - if you focus on an _accurate_ delay. A static

delay differs from rate shaping in use case. In the later we (and probably

you) want a exact/realistic spacing between packets.



Due to timer and scheduling granularity somewhere in between 1bit/s and

10Gb/s netem rate (and tbf) will not scale anymore. You will see burst and

inaccurate spacings, far away from what you want to emulate. For us we want

a realistic and clean behavior, if the result of the emulation is not

identical to the emulated link/device we cannot use it (some background

information). 



Anyway: I was not sure what solution you prefer - for us both are

identical. That's why I presented two solutions, so you can pick up the

favorite one. I will re-code the calculation using a reciprocal divide.

Thanks Eric!



Hagen