Re: zero-copy TCP

From: Ingo Molnar (
Date: Sun Sep 03 2000 - 12:21:50 EST

On Sun, 3 Sep 2000 wrote:

> If we go for a Linux-specific solution anyway, maybe one could add
> another send{,to,msg} flag that makes send*(2)'s buffer access
> non-atomic. That way, the kernel only needs to make sure the pages
> don't disappear, but there's no need for expensive MMU games.
> Of course, this would give applications a way for generating packets
> with an incorrect TCP/UDP checksum, [...]

i believe such zero-copy send should only be allowed for drivers which can
guarantee correct checksums. (ie. cards which do Tx-checksums) The other
drivers will still copy. I dont think this is a problem - the number of
cards that can do scatter-gather DMA but cannot do TX-checksumming is
rather low. (i only know about the Tulip.) All modern cards do
TX-checksumming and scatter-gather DMA.


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