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    SubjectRe: sysconf (was Re: RLIM_INFINITY inconsistency between archs)
    Andi Kleen wrote:
    > H. Peter Anvin wrote:
    > > I don't think we want to do this! IMO, HZ should not get exported to
    > > user space *AT ALL*. Instead, for the few interfaces that need it,
    > > we'll export a "user space HZ" (USER_HZ) which is fixed. No need for
    > > a kernel hack. When we support nonstandard values for HZ, we need to
    > > fix the few interfaces that actually export jiffies values to convert
    > > from "user jiffies" to real jiffies.
    >
    > I think the point is less HZ as unit (it shouldn't be a user visible one),
    > but some programs want to know the timer tick to adapt themselves to it; e.g.
    > to calibrate their timers. Of course it is only an approximation because
    > timer events can always be late in a multitasking environment, but it
    > usually should work out.

    Indeed, such as:

    1. select() up until desired time minus 1 tick.
    2. busy wait using gettimeofday().

    I had to do that to get a simple X snake game to appear smooth on
    Solaris. Though I never did ask Solaris for the HZ value, I just used a
    value that seemed to work well. In this case a self-calibrating method
    would probably be ok -- if you're missing deadlines regularly, increase
    estimate of tick time.

    -- Jamie

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