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Date: Sat, 01 Dec 2012 11:23:00 +0100
From: Andre Oppermann <andre@freebsd.org>
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To: Jack Vogel <jfvogel@gmail.com>
Subject: Re: svn commit: r243714 - in head/sys/dev: ixgbe netmap
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Cc: Jack F Vogel <jfv@freebsd.org>, svn-src-head@freebsd.org,
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On 01.12.2012 10:48, Jack Vogel wrote:
>
>
> On Sat, Dec 1, 2012 at 12:40 AM, Andre Oppermann <andre@freebsd.org <mailto:andre@freebsd.org>> wrote:
>
>     On 30.11.2012 23:19, Jack F Vogel wrote:
>
>         Author: jfv
>         Date: Fri Nov 30 22:19:18 2012
>         New Revision: 243714
>         URL: http://svnweb.freebsd.org/__changeset/base/243714
>         <http://svnweb.freebsd.org/changeset/base/243714>
>
>         Log:
>             First of a series of 11 patches leading to new ixgbe version 2.5.0
>             This removes the header split and supporting code from the driver.
>
>
>     You did this because the datasheet says the header split feature is
>     not supported and using it gives unpredictable results?
>
>
> I'm not sure what the datasheet says, but yes there is a hardware issue
> on some of the 10G adapters if using header split. I have left the code in
> in a disabled state for a long time, thinking it would be there as example
> code, but I think it best to remove it and simplify the code at this point.

It says so in section 7.1.10 Header Splitting:
  Note: Header Splitting mode might cause unpredictable behavior and should not
  be used with the 82599. For more information, see the product specification
  update errata on this subject.

> Oh, and yes, results have always been mixed with the feature in my
> experience anyway.

I can imagine.  Considering how we work with the packet through the stack
and in the socket buffers there isn't much benefit from header splitting.

-- 
Andre