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To: "David S. Miller" <davem@redhat.com>
Cc: kuznet@ms2.inr.ac.ru, scott.feldman@intel.com,
       linux-kernel@vger.kernel.org, linux-net@vger.kernel.org,
       haveblue@us.ibm.com, Manand@us.ibm.com, christopher.leech@intel.com
Subject: Re: TCP Segmentation Offloading (TSO)
References: <288F9BF66CD9D5118DF400508B68C4460283E564@orsmsx113.jf.intel.com.suse.lists.linux.kernel> <200209021858.WAA00388@sex.inr.ac.ru.suse.lists.linux.kernel> <20020903.164243.21934772.taka@valinux.co.jp.suse.lists.linux.kernel> <20020903.005119.50342945.davem@redhat.com.suse.lists.linux.kernel>
From: Andi Kleen <ak@suse.de>
Date: 03 Sep 2002 11:05:30 +0200
In-Reply-To: "David S. Miller"'s message of "3 Sep 2002 10:02:10 +0200"
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"David S. Miller" <davem@redhat.com> writes:

>    From: Hirokazu Takahashi <taka@valinux.co.jp>
>    Date: Tue, 03 Sep 2002 16:42:43 +0900 (JST)
> 
>    I guess it may also depend on bad implementations of csum_partial().
>    It's wrong that some architecture assume every data in a skbuff are
>    aligned on a 2byte boundary so that it would access a byte next to
>    the the last byte where no pages might be there.
>    
> It is real requirement, x86 works because unaligned
> access is handled transparently by cpu.
> 
> But on every non-x86 csum_partial I have examined, worse than
> 2-byte aligned data start is totally not handled.  It is not difficult
> to figure out why this is the case, everyone has copied by example. :-)

x86-64 handles it (also in csum-copy). I think at least Alpha does it 
too (that is where I stole the C csum-partial base from) But it's ugly.
See the odd hack. 

-Andi
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