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Date: Wed, 29 Feb 2012 14:17:56 -0800
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From: Jack Vogel <jfvogel@gmail.com>
To: Rafael Ganascim <rganascim@gmail.com>
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Cc: freebsd-net@freebsd.org
Subject: Re: Igb driver - header split feature
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It seems to help in some workloads, makes little difference in others, and
can even be
less performance in yet others. Its just not a feature that is a 100% win,
that's why its
not on by default. Try it and see.

Cheers,

Jack


On Wed, Feb 29, 2012 at 5:10 AM, Rafael Ganascim <rganascim@gmail.com>wrote:

> Hi list,
>
> I was looking in the igb driver that I use on some Intel nics
> (dualport and quadport gigabit) and in the source code, the feature:
>
> /*
> ** Header split causes the packet header to
> ** be dma'd to a seperate mbuf from the payload.
> ** this can have memory alignment benefits. But
> ** another plus is that small packets often fit
> ** into the header and thus use no cluster. Its
> ** a very workload dependent type feature.
> */
>
> Somebody is using this feature? What's the results?
>
> I think that this feature can be helpfull to improve the performance,
> allowing the processing of the packet headers more fastest (pfills,
> routing, etc). Is this true?
>
> Thanks in advance.
>
> Rafael
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