[lkml]   [2010]   [Mar]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATCH] perf_events: add sampling period randomization support (v2)
    On Thu, Mar 4, 2010 at 3:32 AM, Ingo Molnar <> wrote:
    > * <> 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.
    With perf you also have fixed sampling period (-c option), you simply need to
    express the fact you want it randomized.

    > Thanks,
    >        Ingo

    Stephane Eranian  | EMEA Software Engineering
    Google France | 38 avenue de l'Opéra | 75002 Paris
    Tel : +33 (0) 1 42 68 53 00
    This email may be confidential or privileged. If you received this
    communication by mistake, please
    don't forward it to anyone else, please erase all copies and
    attachments, and please let me know that
    it went to the wrong person. Thanks
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2010-03-04 18:29    [W:0.023 / U:6.556 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site