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    SubjectHow much we can trust packet timestamping
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    Hi all

    IMHO The problem is quite complicated because

    + common hardware is not designed for real time:

    - sends multiple PDUs within one interrupt, and can be delayed
    - Host adapter bus & infraestructure is not designed to garantee latency
    etc...

    + software is also not designed for realtime

    - drivers may timestamp in softirq's
    - irqs has no deterministic latency either
    etc...

    So even if do_gettimeofday() has 1/CPUfreq resolution by using TSC register
    packet timestamping meassurement is biased, how much?

    anybody has studied this? are there reports/doc about this topic?

    of course, this can be avoided by using specialiced hardware, but I'm not
    interested on that and I would like to know how much I can trust this
    timestamps

    Any comment would be greatly appreciated

    Thanks

    Ulisses

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