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    SubjectRe: [Patch 5/6] statistics infrastructure
    Andrew Morton wrote:
    > Martin Peschke <> wrote:
    >> +static int statistic_alloc(struct statistic *stat,
    >> + struct statistic_info *info)
    >> +{
    >> + int cpu;
    >> + stat->age = sched_clock();
    > argh. Didn't we end up finding a way to avoid this?
    > At the least, we should have statistics_clock(), or nsec_clock(), or
    > something which is decoupled from this low-level scheduler-internal thing,
    > and which architectures can implement (vis attribute-weak) if they have a
    > preferred/better/more-accurate alternative.

    I use clocks for two purposes. Both have used sched_clock() so far.

    The statistics infrastructure itself uses a clock only for time stamps
    that tell users what time a statistic has been switched on/off and reset.
    This is what you have spotted here.

    (The other and more important requirement regards exploiters of the
    statistics infrastructure. They need a clock to measure latencies,
    which they can report then.)

    Regarding those time stamps, I think it best to make them look like other
    timestamps, specifically the printk() time stamps in order not to confuse
    users. That is why, one of my patches introduces nsec_to_timestamp()
    based on some lines from printk(). Printk() uses printk_clock() as
    source, which is nothing else than a sched_clock() call, unless
    reimpelmented by architectures (only done for ia64).
    If I want similar timestamps, I need the same time source too.

    Now my question:

    Would I get away with making printk_clock() a timestamp_clock() that
    should be used by anyone exporting nsec_to_timestamp()-formated time
    stamps to user space, including me?

    I would then continue to see the use of sched_clock() in printk_clock()
    ... aehm timestamp_clock() as somebody else's problem (or at least
    as a subordinate problem).
    Thoughts? <ducking down>


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