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    SubjectRe: [PATCH] perf_events: add sampling period randomization support (v2)
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    On Thu, Mar 4, 2010 at 3:32 AM, Ingo Molnar <mingo@elte.hu> wrote:
    >
    > * eranian@google.com <eranian@google.com> wrote:
    >
    >> This patch adds support for randomizing the sampling period.  Randomization
    >> is very useful to mitigate the bias that exists with sampling. The random
    >> number generator does not need to be sophisticated. This patch uses the
    >> builtin random32() generator.
    >
    >> +     if (width > 63 || attr->freq)
    >> +             return -EINVAL;
    >
    > Why not for freq counters? Those are semi-randomized already, but it might
    > make sense to make them 'more' randomized in special circumstances. That would
    > also allow us to enable the randomization in perf top and perf record, by
    > default.
    >
    What's the goal of freq?
    Achieve and maintain the target interrupt/rate.
    In doing so, it has to adjust the period (not randomly).

    Randomization may prevent achieving the rate, or it may slow
    it down. What's the value add of that?

    > Without that we'd have no immediate usecase and no way to ensure that this
    > code works as intended.
    >
    Why?
    With perf you also have fixed sampling period (-c option), you simply need to
    express the fact you want it randomized.

    > Thanks,
    >
    >        Ingo
    >



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