Re: Why HZ on i386 is 100 ?

Andi Kleen
2002-04-23T07:17:28Z

Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

> > The problem is in accounting (or time slicing if you prefer) where we
> > need to start a timer each time a task is context switched to, and stop
> > it when the task is switched away. The overhead is purely in the set up
> > and tear down. MOST of these never expire.
>
> Done properly on many platforms a variable tick is very very easy and also
> very efficient to handle. X86 is a paticular problem case because the timer
> is so expensive to fiddle with

Depends. On modern x86 you can either use the local APIC timer or
the mmtimers (ftp://download.intel.com/ial/home/sp/mmts097.pdf -
should be in newer x86 chipsets). Both should be better than the
8254 timer and are also not expensive to work with.

-Andi