Re: finding out the value of HZ from userspace

[Jamie Lokier]

Peter Williams wrote:
> >When we go to a tickless kernel and offer high-resolution timers to
> >userspace, then it will be irrelevant.  Until then, or if the kernel
> >goes tickless but limits the resolution of timers for efficiency, the
> >value of HZ is still relevant.
> 
> The resolution will always be limited.  That's the nature of digital 
> systems.  Unlimited resolution would require real "real" numbers and 
> that's not possible.  The nearest you get on a digital system is the 
> floating point APPROXIMATION to real numbers.

Sure, but HZ will still be irrelevant.  There won't be a HZ to report.

> IMHO, as I've said several times, USER_HZ should be changed to be equal 
> to or greater than HZ.  In fact, if having USER_HZ greater than HZ would 
> still make it unusable for your purposes, I'd change that opinion to say 
> USER_HZ should be equal to HZ (or, in other words, cease to exist).

It's not possible to change USER_HZ.  There are too many programs with
the number hard-coded into the binary.  The best we could do is make
the HZ userspace macro non-constant, so it calls sysconf(_SC_CLK_TCK),
and wait a few years until practically all programs being used no
longer contain a hard-coded constant.  Then we could get rid of USER_HZ again.

-- Jamie
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