Issues with a Large Fat pipe Network simulation

[Luigi Rizzo]

On Mon, Jun 20, 2005 at 11:14:53PM +0200, Pieter de Boer wrote:
> Luigi Rizzo wrote:
...
> However.. when I deleted the pipe rules on 'network', the speed suddenly 
> went up to around 800mbit/s too! I remade them, and voila, 200mbit/s.

network emulation is a tricky job :)

in any case i believe what happens is the following.

The pipe has a default size of 50 slots, which at 1500 bytes is
little above 64k. If the sender is bursting a large number of packets,
it may well overflow the pipe's queue causing a backoff (which
may simply be immediate, or delayed, depending on how you configure
various things).

I believe setting the queue size in the pipe to a value larger than
the window should fix things.

can you confirm that ?

	cheers
	luigi

> So apparantly it's an issue in the dummynet configuration I have. So, to 
> reiterate:
> 
> On 'network':
> pipe 1 from client to server via em0
> pipe 2 from server to client via em1
> allow ip from any to any

i am
> Will give me 200MBit/s when using 128KB window sizes, but 800MBit/s when 
> using 64KB window sizes.
> 
> On 'network':
> allow ip from any to any
> 
> Will give me 800Mbit/s when using 64KB or 128KB window sizes. I haven't 
> configured the pipes in any way, though.
> 
> 
> So it appears it's due to the 'network' box afterall..
> 
> -- 
> Pieter