Messages in this thread | | | Date | Thu, 3 Jun 1999 00:13:33 -0400 | From | Johannes Erdfelt <> | Subject | Re: zero-copy TCP fileserving |
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On Wed, Jun 02, 1999, Oliver Xymoron <oxymoron@waste.org> 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 ? > > > > What I mean is, when tcp does a sendmsg, it shouldn't need to copy the > > actual data into the skbuf, but merely the headers, and remember a ptr to > > the data area (which would have to be locked down until the fragment is > > acked or the connection breaks, of course). Then the network driver could > > (if it supports s/g DMA) send the headers + data directly from memory. > > 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? Also, the decreased memory usage is also a (not as significant) win.
Albeit, the architecture to support hardware checksums isn't in place, but that can be worked on.
> 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.
JE
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