netdev - Re: [RFC] New Qlogic 10Gb Ethernet driver for 2.6.28

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Message-ID: <20080826093632.GW7908@solarflare.com>
Date:	Tue, 26 Aug 2008 10:36:33 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>, jeff@...zik.org,
	Linux-Driver@...gic.com, netdev@...r.kernel.org
Subject: Re: [RFC] New Qlogic 10Gb Ethernet driver for 2.6.28

Ron Mercer wrote:
> On Fri, Aug 22, 2008 at 02:43:43PM -0700, David Miller wrote:
> > From: Ron Mercer <ron.mercer@...gic.com>
> > Date: Fri, 22 Aug 2008 10:46:26 -0700
> > 
> > > On Fri, Aug 22, 2008 at 02:42:52AM -0700, David Miller wrote:
> > > > I also notice that this driver does not do:
> > > > 
> > > > 	skb_reserve(skb, NET_IP_ALIGN);
> > > > 
> > > > on RX packets to get the IP headers properly 4-byte aligned aligned
> > > > after the ethernet header.
> > > 
> > > The chip currenly has problems with 2-byte aligned receive buffers.
> > > It will be fixed in the next turn.
> > 
> > If the chip cannot handle this, you will need to copy into a properly
> > aligned buffer.
> > 
> > Otherwise some RISC platforms will take unaligned access traps, which
> > run extremely slowly, when 32-bit and larger members of the protocol
> > headers are read by the networking stack.
> 
> I see your point.  I will add the re-alignment but would like to jump
> over it for platforms that don't need it.  Is there a list somewhere of
> the RISC platforms that take a trap on unaligned accesses?  Or better
> yet, a list of those that don't?

You can use #ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
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