Re: finding out the value of HZ from userspace

[Bernd Petrovitsch]

On Die, 2004-03-16 at 06:53, Peter Williams wrote:
> Andi Kleen wrote:
> > Peter Williams <peterw@xxxxxxxxxx> writes:
[...]
> > Already exists for a long time - AT_CLKTCK. glibc has a nice wrapper
> > for it too (sysconf)
> 
> So it does and POSIX.1 (_SC_CLK_TCK) compliant as well.  Unfortunately, 
> the presence of this functionality makes it VERY difficult to understand 
> why ticks are being converted from HZ==1000 values to HZ=100 values when 
> they are being exported to user space especially as this conversion 
> throws away precision.  Can anyone enlighten me?

1) Because Linux had long time HZ=100 hardcoded (except on Alphas) and
   lots of applications probably use that value today (as HZ in their
   source and not sysconf(...))  - especially since 2.4 (at least most
   of them) has HZ=100 except for 64bit CPUs).
2) There are patches which dynamically change the CPU speed. And it
   probably (IMHO) makes sense to change HZ dynamically too in that
   situations. And a over-time changing HZ value is useless in
   user-space.

	Bernd
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