Messages in this thread | | | Subject | Re: finding out the value of HZ from userspace | From | Bernd Petrovitsch <> | Date | Tue, 16 Mar 2004 10:16:45 +0100 |
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On Die, 2004-03-16 at 06:53, Peter Williams wrote: > Andi Kleen wrote: > > Peter Williams <peterw@aurema.com> 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 -- Firmix Software GmbH http://www.firmix.at/ mobil: +43 664 4416156 fax: +43 1 7890849-55 Embedded Linux Development and Services
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