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SubjectRe: Efficient IPC mechanism on Linux
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On Wed, 2003-09-10 at 11:18, Luca Veraldi 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.

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