netdev - Re: alignment faults in 3.6

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Message-ID: <1349952970.1232.5.camel@sakura.staff.proxad.net>
Date:	Thu, 11 Oct 2012 12:56:10 +0200
From:	Maxime Bizon <mbizon@...ebox.fr>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Måns Rullgård <mans@...sr.com>,
	Jon Masters <jonathan@...masters.org>, netdev@...r.kernel.org,
	David Laight <David.Laight@...LAB.COM>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: alignment faults in 3.6

On Thu, 2012-10-11 at 12:49 +0200, Eric Dumazet wrote:

> So if you have an alignment fault, thats because IP header is not
> aligned on 4 bytes ?
> 
> If so a driver is buggy and must be fixed.

So a driver that does not align the ip header is buggy ?

I always thought it was ok not to do so (with a potential performance
penalty).

I have some MIPS hardware that is not able to DMA on anything but 32bits
aligned addresses (bcm63xx). I tried once to add a memcpy instead of
taking unaligned faults and the result was *much slower* on a ipv4
forwarding test (which is what the hardware is used for).

-- 
Maxime

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