Re: Why HZ on i386 is 100 ?

[John Alvord]

On Sun, 21 Apr 2002, Pavel Machek wrote:

> Hi!
> 
> >   Davide> i still have pieces of paper on my desk about tests done on
> >   Davide> my dual piii where by hacking HZ to 1000 the kernel build
> >   Davide> time went from an average of 2min:30sec to an average
> >   Davide> 2min:43sec. that is pretty close to 10%
> > 
> > The last time I measured timer tick overhead on ia64 it was well below
> > 1% of overhead.  I don't really like using kernel builds as a
> > benchmark, because there are far too many variables for the results to
> > have any long-term or cross-platform value.  But since it's popular, I
> > did measure it quickly on a relatively slow (old) Itanium box: with
> > 100Hz, the kernel compile was about 0.6% faster than with 1024Hz
> > (2.4.18 UP kernel).
> 
> .5% still looks like a lot to me. Good compiler optimization is .5% on 
> average...
> 
> And think what it does with old 386sx.. Maybe time for those "tick on demand"
> patches?

Doesn't IBM have a tickless patch.. useful when demonstrating 10,000
virtual linux machines on a single system.

john alvord