netdev - Re: [PATCH] [NIU] VLAN does not work with niu driver

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Date:	Wed, 09 Sep 2009 18:10:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	Matheos.Worku@....COM
Cc:	Joyce.Yu@....COM, netdev@...r.kernel.org
Subject: Re: [PATCH] [NIU] VLAN does not work with niu driver

From: Matheos Worku <Matheos.Worku@....COM>
Date: Wed, 09 Sep 2009 18:01:23 -0700

> The frame type in NIU HW is embedded in a HW header, so it is possible
> to check the HW header and decide whether to pull up ETH_HLEN or VLAN
> header size of bytes. However, considering the amount of work required
> to get and examine the HW header (including endianess issues), we
> thought pulling up 64 bytes by default (as used in cassini.c) would be
> efficient.

Well, it was 64 in early versions of the driver, and I decreased it
down to ETH_HLEN.

The less the better since for forwarding applications anything past
the IPV4 header pulled is going to be a waste of CPU cache lines and
thus negatively effect forwarding rates.

That's why I asked if this change was performance regression tested,
because I know it's going to slow down forwarding rates for small
packets.
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