Re: Why HZ on i386 is 100 ?

Richard B. Johnson
2002-04-16T12:30:15Z

On Tue, 16 Apr 2002, William Lee Irwin III wrote:

> On Tue, Apr 16, 2002 at 09:47:48AM +0200, Olaf Fraczyk wrote:
> > Hi,
> > I would like to know why exactly this value was choosen.
> > Is it safe to change it to eg. 1024? Will it break anything?
> > What else should I change to get it working:
> > CLOCKS_PER_SEC?
> > Please CC me.
> > Regards,
> > Olaf Fraczyk
>
> I tried a few times running with HZ == 1024 for some testing (or I guess
> just to see what happened). I didn't see any problems, even without the
> obscure CLOCKS_PER_SEC ELF business.
>
>
> Cheers,
> Bill
> -

On Version 2.3.17, with a 600 MHz SMP Pentium, I set HZ to 1024 and
recompiled everything. There was no apparent difference in performance
or "feel".

Note that HZ represents the rate at which a CPU-bound process may
get the CPU taken away. Real-world tasks are more likely to be
doing I/O, thus surrendering the CPU, before this relatively long
time-slice expires. I don't think you will find any difference in
performance with real-world tasks. FYI, the Alpha uses 1024 simply
because the timer-chip can't divide down to 100 Hz.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).

Windows-2000/Professional isn't.