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    SubjectRe: [RFC PATCH 1/3] Unified trace buffer

    On Fri, 26 Sep 2008, Ingo Molnar wrote:
    >
    > Firstly they need a low-frequency (10khz-100khz) shared clock line
    > across all CPUs. A single line - and since it's low frequency it could
    > be overlaid on some existing data line and filtered out. That works
    > across NUMA nodes as well and physics allows it to be nanosec accurate
    > up to dozens of meters or so.

    Can this possibly be true? I mean, light travels only one foot every
    nanosecond. Can it really keep nanosecond accuracy up to dozens of meters
    away? If you send the same signal to CPU1 that is 1 foot away, as well as
    send it to CPU2 that is 2 feet away. CPU2 will get that signal at least 1
    nanosec after CPU1 receives it.

    Of course if the hardware is smart enough to know this topology, then it
    could account for these delays in traffic.

    -- Steve



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