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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