Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt

Maciej W. Rozycki
2005-07-14T09:56:53Z

On Wed, 13 Jul 2005, Lee Revell wrote:

> Did anyone else find this strange:
>
> "The RTC is used in periodic mode to provide the system profiling
> interrupt on uni-processor systems and the clock interrupt on
> multi-processor systems."
>
> We just take NR_CPUS * HZ timer interrupts per second, what's the
> advantage of using the RTC?

It tends to work in the APIC mode all the time (with all systems), unlike
the PIT which has "interesting" routing problems with its IRQ0, which
you've probably already noticed. Have a look at all the hassle in
check_timer() if you want to double-check it.

Of course using APIC internal timers is generally the best idea on SMP,
but they may have had reasons to avoid them (it's not an ISA interrupt, so
it could have been simply out of question in the initial design).

Maciej