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    SubjectRe: lockdep oddity
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    On Wed, 2006-09-06 at 10:40 +0200, Ingo Molnar wrote:
    > * Hua Zhong <hzhong@gmail.com> wrote:
    >
    > > We are just trading accuracy for speed here.
    >
    > no, we are trading _both_ accuracy and speed here! a global 'likeliness'
    > pointer for commonly executed codepaths is causing global cacheline
    > ping-pongs - which is as bad as it gets.

    Up stream or no, would be better for it to again be light weight.

    > the right approach, which incidentally would also be perfectly accurate,
    > is to store an alloc_percpu()-ed pointer at the call site, not the
    > counter itself.

    I don't think it could be done via the macro. If it were called during
    run time it would have to be special alloc_percpu() that didn't call
    back into the profiling code (which almost everything does do).

    > the current code needs more work before it can go upstream i think.

    It was never really planned to go upstream. It's ultimately a debugging
    feature that's really only needed in -mm ..

    Daniel

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