Messages in this thread | | | Date | Fri, 7 May 1999 13:03:33 -0400 (EDT) | From | Zach Brown <> | Subject | Re: Mark Russinovich's reponse Was: [OT] Comments to WinNT Mag !! (fwd) |
| |
On Sat, 8 May 1999, Chris Wedgwood wrote:
> Could someone please clue me in on how this works? I don't understand > how we can do zero copy without hardware checksumming... and in the > cases we do, surely the overhead of twiddling this hardware is > comparable to copying 1500 bytes of data? (For HIPPI I can see it > might make sense).
As Alan said, you get it mostly for free. in the case of the 905b (aside from sun's stuff, the only 100mb pci card I know of that can do hw csum) its merely some bits to set in the descriptors that we pass the card anyway. but once you do this you can start passing the card iovec style packets. this makes frag calculation simple iovec math rather than copy/csum operations, and in the easiest sendfile() case we can dma pages right out from the page cache, no memory sitting around in skbs for us to touch/manage/etc.
of course, the book keeping is not exactly trivial.
-- zach
- - - - - - 007 373 5963
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
| |