There's a parameter in one of the fundamental header files
called HZ which defines the frequency of the system clock.
In a default system, this has the value 100. I know some
people who have played with this value to get finer
scheduling within a standard Linux system and I've heard of
values up to several tens of thousands Hz, but the usual
comment is that the higher the value the more sluggish the
command-line response of the system because a higher
percentage of the time is spend in scheduling and
bookkeeping operations; that was with 66 & 100 MHz '486s
and I imagine that with a 1 GHz P-III 50-100 KHz would be
attainable. This frequency which corresponds to the jiffy
is fixed at the time the kernel is compiled.
What is computed dynamically out at boot time is a constant
which Linus called bogomips which is used to calibrate
software timing loops within the kernel.
Norm
----- Original Message -----
From: Chunky Kibbles <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Saturday, October 13, 2001 7:08 AM
Subject: Re: [rtl] Help on real time scheduling
> On Fri, Oct 12, 2001 at 12:24:00PM -0400, Dresner, Norman
A. wrote:
> > You're probably using a computer with an x86
architecture. AFAIK, every
> > Linux implementation except the Alpha CPU uses a clock
rate (jiffies) of 100
> > Hz or 10 ms; the Alpha uses 1 Khz. Your choices then
are:
> > 1. Use an Alpha with normal Linux and hope for the best
> > 2. Use Real-Time Linux (RTLinux) on any platform it's
been ported
> > to.
>
> Hang on.
>
> Aren't jiffies worked out at boot-time, or is that only
because I've
> only read the source for the x86?
>
> I'm sure I remember linux doing some timing loops to
discover
> BogoMips, then working out how big a jiffy is from there?
>
> [Note: I _would_ read the source, except my machine went
out of
> contention and now I'm on a friend's box that's only
windows]
>
> Gary (-;
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