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    SubjectRe: Efficient IPC mechanism on Linux
    On Wed, Sep 10, 2003 at 10:52:55AM +0100, Jamie Lokier wrote:
    > Arjan van de Ven wrote:
    > > > The overhead implied by a memcpy() is the same, in the oder of magnitude,
    > > > ***whatever*** kernel version you can develop.
    > >
    > > yes a copy of a page is about 3000 to 4000 cycles on an x86 box in the
    > > uncached case. A pagetable operation (like the cpu setting the accessed
    > > or dirty bit) is in that same order I suspect (maybe half this, but not
    > > a lot less). Changing pagetable content is even more because all the
    > > tlb's and internal cpu state will need to be flushed... which is also a
    > > microcode operation for the cpu. And it's deadly in an SMP environment.
    > I have just done a measurement on a 366MHz PII Celeron

    This test is sort of the worst case against my argument:
    1) It's a cpu with low memory bandwidth
    2) It's a 1 CPU system
    3) It's a pII not pIV; the pII is way more efficient cycle wise
    for pagetable operations

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