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    SubjectRe: [patch 0/3] [Announcement] Performance Counters for Linux
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    From: Ingo Molnar <mingo@elte.hu>
    Date: Fri, 5 Dec 2008 09:42:33 +0100

    > Please let me repeat: it's a _fundamental_ thesis of performance
    > instrumentation to not disturb the monitored context. Your insistence on
    > _stopping_ the monitored task breaks that fundamental axiom!

    This is only a problem if you make your measurement quantums too
    small.

    Furthermore, there are multiple registers and states to update
    atomically when a perf counter overflows. You're read/write thing
    just doesn't cut it, especially for certain kinds of hardware.

    It's really a utopian view of the world. :)



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