Re: zero-copy TCP

From: Andi Kleen (
Date: Sun Sep 03 2000 - 05:08:08 EST

On Sun, Sep 03, 2000 at 10:18:50AM +0200, Ingo Molnar wrote:
> On 2 Sep 2000, Jes Sorensen wrote:
> > You can't DMA directly from a file cache page unless you have a
> > network card that does scatter/gather DMA and surprise surprise,
> > 80-90% of the cards on the market don't support this. [...]
> exactly. The TUX patch solves this by copying 'multi-fragment skbs' into a
> temporary single-fragment skb, if the card doesnt support scatter-gather,
> 64-bit DMA. This way the copying is delayed as much as possible, to the
> point where we queue the packet to the network device.

I did the same for fragment RX some months ago (simple fragment lists that
were copy-checksummed to user space). Overall it is probably better to use
a kiovec, because that can be more easily used in nfsd and sendfile.

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