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SubjectRe: zero-copy TCP fileserving
On Wed, 2 Jun 1999, Oliver Xymoron wrote:
> On Wed, 2 Jun 1999, Bjorn Wesen wrote:
> > Speaking of shortcuts, what is the status of some sort of direct
> > page -> skb TCP sending ?
>
> This simple zero-copy isn't really a win on most PC hardware as it takes
> about the same amount of time to do a checksum as it does to do a checksum
> and copy.

But for the hardware I'm running this on, a checksum + copy takes at least
twice the time as a checksum (simple - read vs read/write). And this is
the main bottleneck. Sure, on a P2/400 this is not an issue but it is for
other systems, like embedded ones trying to run at 100 mbit/s.

> A more powerful scheme is being investigated by sct and a couple others. A
> related scheme worked out on FreeBSD and presented at a recent Usenix
> could cache checksums, for example.

Doesn't get rid of the unnecessary copying though.

/Bjorn



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