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    SubjectRe: [RFC 1/3] Framework for accurate node based statistics
    On Tue, Dec 06, 2005 at 11:36:43AM -0800, Christoph Lameter wrote:
    > On Tue, 6 Dec 2005, Andi Kleen wrote:
    > > > Yuck. That code uses atomic operations and is not aware of atomic64_t.
    > > Hmm? What code are you looking at?
    > include/asm-generic/local.h. this is the default right? And
    > include/asm-ia64/local.h.
    > > At least i386/x86-64/generic don't use any atomic operations, just
    > > normal non atomic on bus but atomic for interrupts local rmw.
    > inc/dec are atomic by default on x86_64?

    They are atomic against interrupts on the same CPU. And on Linux
    also atomic against preempt moving you to another CPU. And all that
    without the cost of a bus lock. And that is what local_t is about.

    > > Do you actually need 64bit?
    > 32 bit limits us in the worst case to 8 Terabytes of RAM (assuming a very
    > small page size of 4k and 31 bit available for an atomic variable
    > [sparc]). SGI already has installations with 15 Terabytes of RAM.

    Ok we'll need a local64_t then. No big deal - can be easily added.
    Or perhaps better a long_local_t so that 32bit doesn't need to
    pay the cost.


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