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

Venkatesh Pallipadi
2005-07-15T18:14:06Z

On Fri, Jul 15, 2005 at 07:57:01PM +0200, Andi Kleen wrote:
> > I wouldn't say it is totally impossible. There are ways in which Linux can work
> > without a reliable Local APIC timer. One option being - make one CPU that gets
> > the external timer interrupt multicast an IPI to all the other CPUs that
> > wants to get periodic timer interrupt.
>
> That doesn't mix very well with variable ticks. And I believe
> we really need them.

It should work with variable ticks as we can easily add/remove CPUs from this
multicast destination.

> For no tick in idle you need a timer for each CPU that
> can be programmed to a reasonably long interval to wake you
> up after longer idleness. And all that
> should work without bouncing cache lines around all the time
> because that doesn't work on larger systems.

And each CPU timer itself does very little writes in terms of caches. The
two things that happen here are scheduler_tick and kstat_accounting.
Or am I missing something? Did you have anything specific in mind wrt
bouncing cachelines?

Thanks,
Venki