Messages in this thread | | | Date | Sun, 3 Sep 2000 05:22:44 +0200 | From | Jamie Lokier <> | Subject | Re: zero-copy TCP |
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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. Besides that you > need to do copy-on-write if you want to be able to do zero copy on > write() from user space, marking data copy on write is *expensive* on > x86 SMP boxes since you have to modify the tlb on all > processors. On top of that you have to look at the packet size, for > small packets a copy is often a lot cheaper than modifying the page > tables, even on UP systems so you need a copy/break scheme here.
I just thought I'd mention that you can do zero copy TCP in and out *without* any page marking schemes. All you need is a network card with quite a lot of RAM and some intelligence. An Alteon could do it, with extra RAM or an impressively underloaded network.
(for example) http://www.digital.com/info/DTJS05/
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