Re: HZ from userspace

["Ray Lee" <ray-lk@madrabbit.org>]

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On Wed, Aug 6, 2008 at 3:16 PM, Ray Lee <ray-lk@madrabbit.org> wrote:> On Wed, Aug 6, 2008 at 3:07 PM, Piotr Jaroszyński> <p.jaroszynski@gmail.com> wrote:>>>> I want to be able to convert starttime from /proc/#/stat to absolute>>>> time and it seems that I need HZ to do that as it is measured in>>>> jiffies. How can I get HZ? I have seen some discussion about this but>>>> haven't found a definite answer. procps is using some hacks do it and>>>> I would prefer to avoid them.>>>> I only need a solution for modern kernels, say 2.6.20+ if that matters.>>>>>> `man sysconf`, in particular you want sysconf(_SC_CLK_TCK).>>>> manpage says it's obsolete and i read in some discussion that it only>> returns the default and not the real HZ used.>> I believe the claim that it's out of date is out of date. manpages> 3.0.1 has an update to this, according to a message I saw on this list> a month or so ago.>> Regardless, the fields you're reading should all be showing USER_HZ> which is fixed at 100 per second regardless of the underlying kernel> HZ parameter.>> Try it.>
Here's the latest proc(5) man page from June 25, 2008. Look for_SC_CLK_TCK about a third of the way down.
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