netdev - Re: TCP communication for raw image transmission

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Date:	Mon, 02 Jan 2012 16:59:03 +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 16:21 +0100, Jean-Michel Hautbois a écrit :
> Hi all,
> 
> I am currently working on a way to send raw images (~400*300 YUV
> 4:2:0) at a relative high speed (raw image and not compressed image
> due to specific codec issues).
> This would represent about 57MBps/sec on a 100Mbps ethernet link.
> This link is direct, nothing else will pass through it.
> 
> My question is a performance and efficiency question. Here is what I
> am thinking about :
> - I have the image on one computer at a known memory adress
> - I want top transmit this picture using TCP packets with the rule
> "1row = 1packet", maybe "2rows=1packet"
> - All these packets have to go on an ethernet link and will be
> received on another computer starting at a known memory adress
> Something like this :
> http://imageshack.us/photo/my-images/15/tcpmemory.png/
> 
> I was thinking about using TCP socket (of course) and the sendfile
> syscall on sender side, splice syscall on the receiver side, but I
> don't know if this is the best (and fastest) way to do it ?
> I would like to avoid memory copy as much as possible as the systems
> on which it will be done are embedded arm computers.
> TCP is chosen in order to get ordered packets, but maybe am I wrong ?
> 
> Thanks for any clues you can give !
> Regards,
> JM
> --

Do you really need full image, or are some missing lines allowed ?

What is the length in bytes for a line ?

TCP stream and your bandwidth requirements would work only if you
guarantee not a single packet loss.

Using UDP (RTP) would allow you to respect any time limits at the
sender, yet allowing some drops on the network.

If you use a direct link, packets wont be re-ordered.

Is your ARM platform so slow it cannot afford copying 10 Mbytes per
second in skb ?



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