netdev - Re: TCP communication for raw image transmission

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Date:	Mon, 02 Jan 2012 17:52:17 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jean-Michel Hautbois <jhautbois@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: TCP communication for raw image transmission

Le lundi 02 janvier 2012 à 17:40 +0100, Jean-Michel Hautbois a écrit :

> Mmmh, using netperf you would like to know what the client (my ARM
> board) can do ?
> How would you test it ? I can have an ARM board on one side, and the
> x86 on the other...
> 

x86> netserver &
arm> netperf -H <arm_ip_address> -l 60 -t TCP_STREAM

1) check cpu usage on <arm> while test is running 
(for example : vmstat 1 )
2) check bandwith of test run 


> Yes, the idea of limiting tcp frame to 2 lines is to avoid
> fragmenting. So, with a MTU at 1500, MSS=1460, I can put 2 lines <=
> 730bytes. I will probably have ~700bytes.

There is no fragmentation on TCP.

You should just let TCP stack use the best MSS (MTU - 40 or so), to
lower cpu usage both on sender and receiver.

Eventually, check if you can use a big MTU on your dedicated ethernet
link to fit 4 lines per tcp frame.



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