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SubjectRe: zero-copy TCP fileserving
On Thu, 3 Jun 1999, Johannes Erdfelt wrote:

> > 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.
>
> What about the new network cards which can do checksums in hardware?

That's currently a special case. The architecture is optimized for the
common case and currently compares quite favorably to other systems, even
those that use zero-copy approaches..

> > 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.
>
> Hmm, caching checksums? I wonder how that would work. It would only work
> on data which is somewhat repeated. This would probably be a no win for
> encrypted data. Albeit, I haven't read the paper yet, so I dunno how it
> works.

The Linux network stack is much faster than any decent software encryption
scheme, all of which make a dozen or more read/write rounds on its
input, so that isn't a very interesting case. The interesting cases for
networking are file and web serving, and these seem fairly amenable to the
IO-Lite style approach (even some dynamic content).

--
"Love the dolphins," she advised him. "Write by W.A.S.T.E.."


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