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    SubjectRe: PATCH: Raw device IO for 2.1.131
       From: (Alan Cox)
    Date: Sat, 12 Dec 1998 23:32:08 +0000 (GMT)

    > - real work. If zero-copy makes a real difference, you'd better
    > buy a new
    > computer, because your memory subsystem is too slow. Either
    > you're IO

    Every computer on the planet has a memory subsystem that is too
    slow, thats why we have cache. Zero copy makes a difference on real
    world networking. Real world file and web serving is about
    blasting arbitary blocks of data from memory to and from networks.

    I completely agree with Alan.

    Linus, if what you want to say is that it's "ok" to have the data go
    in and out of the CPU cache for every I/O, and that twiddling block
    and inode allocation bits in the filesystem code is "ok" for every
    I/O, then you need to have your head seriously examined.

    I want 100% of my memory bandwidth, and that means:

    1) making the data go once over the memory bus
    2) never having the data hit the cpu cache
    3) the data path must be user data --> device, no bulky VFS sitting
    in the middle dirtying inode and block tables along the way

    Why should the hardware people build faster memory subsystems if the
    software people are just going to use it half-assedly? Thats what M$
    does, but we shouldn't.

    David S. Miller

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