Re: [patch] genapic: optimize & fix APIC mode setup

[Ingo Molnar <mingo@elte.hu>]

* Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:

> On Mon, Nov 13, 2006 at 07:42:56PM +0100, Ingo Molnar wrote:
> > * Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:
> > > Not really. That chipset belongs to a MP platform and with your 
> > > proposed patch, we will endup using clustered APIC mode and will hit 
> > > the issue(in the presence of cpu hotplug) mentioned in that URL.
> > 
> > hm, why does it end up in clustered mode? Cluster mode should only 
> > trigger if the APIC IDs go beyond 16.
> 
> go beyond '8' not 16. With Dual-core+HT these MP platforms will have 
> 16 logical cpus.

yes - then the APIC ids will go beyond 15.

> > but i'd be fine with never going into cluster mode, instead always 
> > using physical flat mode when having more than 8 APICs (independent 
> > of the presence of CPU hotplug). On small systems, logical flat mode 
> > is what is the best-tested variant (it's also slightly faster).
> 
> Ok.

ok, that's really good. Is there any 'weird' platform that you are aware 
of that absolutely needs clustered APIC mode (because it has no physical 
delivery mode or something)?

	Ingo