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    SubjectRe: Thread implementations...


    On Wed, 24 Jun 1998, David S. Miller wrote:

    > Just an idea I had... and it would work. I still think the TLB
    > thrashing costs of mmap() compared to write() (the kernel has large
    > PTE's so write is unfortunately almost always faster under Linux) is
    > going to show up still to some extent, and there isn't much we can do
    > about that.

    Oh yeah, that bites. What about when you use net cards with on-card
    packet assembly? I suppose then it matters whether you can send them v or
    p addresses for DMA... the v->p has to be paid somewhere. No wait, you
    can pre-pay the v->p as long as the p doesn't change... you pay it once
    the first time the file is sent, but then you can re-use the same list of
    commands for future attempts.

    > The main reason you want mmap() (or sendfile()) over read() is to be able
    > to perform single-copy and zero-copy TCP. read() with page-flipping is
    > another way to do it, but I really don't know the difficulty.
    >
    > Be careful what you talk about. write() is not nearly as difficult to
    > get zero-copy out of as read(), read() is very difficult without very
    > specialized hardware and MTU's > PAGE_SIZE as well.

    Hey I'm a webserver guy, I only care about writing to sockets ;)

    Dean



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