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Date:	Thu, 7 Aug 2008 14:15:35 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	bhutchings@...arflare.com, buytenh@...tstofly.org,
	netdev@...r.kernel.org, akarkare@...vell.com, nico@....org,
	dale@...nsworth.org
Subject: Re: using software TSO on non-TSO capable netdevices

On Wed, Aug 06, 2008 at 11:07:41PM -0700, David Miller wrote:
>
> We don't touch anything in the original TSO skb.  However we expand
> the headroom (if necessary) and in the area in front of skb->data we
> build the header areas for the sub-TSO frames, one by one.

Or we could just allocate them beforehand, either way, it's one
operation per superpacket so it's cheap.
 
> This might be where we get pushed over the edge and have to add a
> dma_addr_t to sk_buff and skb_frag_struct.  And that might not
> be such a bad thing because it will allow other things that
> we've always wanted to do.

Since the skb_frag struct is in the shared area where we have
to pad up to a power-of-two for kmalloc we usually have plenty
of free space anyway.

> Another nice aspect of this idea is that we can make the existing GSO
> code just build this funny "TSO plus hidden headers" SKB, and then do
> the by-hand unpacking into new SKB chunks that we will let smart
> drivers do directly into their TX rings.
> 
> Herbert what do you think?

Yes this idea sounds perfect :)

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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