linux-kernel - Re: Ethernet driver problem

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Date:	Wed, 10 Oct 2007 11:49:58 -0400
From:	"linux-os \(Dick Johnson\)" <linux-os@...logic.com>
To:	"Jupe" <jupejupe@...hpost.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: Ethernet driver problem

On Wed, 10 Oct 2007, Jupe wrote:

> Hi,
>
> I have written an ethernet driver for an ARM based board.
> Linux version: 2.6.20.1
>
> Ping is working fine.
>
> I have written a test server/client application using socket programming
> (TCP).
> After the connection is setup the server sends a file to the client.
>
> When I run server on PC and client on ARM board it works without any
> problem.
>
> BUT if I run server on ARM board and client on PC, it works for some
> time and
> then the speed is drastically reduced. (I am sending 4k of data each
> time.
> after 50 sends it reduces its speed.  This happens always.)
>
> I did some debugging and found that after 50 sends, tcp_sendmsg() is not
> being
> called at the same frequency before slowdown.  Also when my driver
> ether_tx seems to
> be working fine.
>
> But still i am not able to get the reason for this behaviour.  Can
> anyone give hints as to
> why this is happening?
>
>
> Regards
> Jupe
>
> -- 
>  Jupe
>  jupejupe@...hpost.com
>
> -- 
> http://www.fastmail.fm - mmm... Fastmail...

First, does your TCP/IP test application work okay on
a Linux machine that does not use your new driver?

That's the first thing to test.

Next, is auto-negotiation working correctly in your
driver? If you don't have auto-negotiation, have you
set the Ethernet parameters correctly so that BOTH
the server and the client use either full-duplex, or
half-duplex, without mixing them up?

Next, make sure that you are properly handling
transmit retries (handling all possible errors)
in your driver. The transmitter does not want
to drop packets if there is no room in the
device, only the receiver should drop packets
if there are no buffers. You do not want
the TCP/IP replacement algorithm to request
missing packets because this slows everything
down. Again, in the transmitter section
of your driver, consider data precious.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.59 BogoMips).
My book : http://www.AbominableFirebug.com/
_

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