Re: More than 8 CPUs detected and CONFIG_X86_PC cannot handle it on 2.6.16-rc6

[Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>]

On Sun, Mar 12, 2006 at 02:05:00PM +0100, Krzysztof Oledzki wrote:
> 
> 
> On Sun, 12 Mar 2006, Andrew Morton wrote:
> 
> > Krzysztof Oledzki <olel@ans.pl> wrote:
> >>
> >> On Sat, 11 Mar 2006, Andrew Morton wrote:
> >>
> >> > Krzysztof Oledzki <olel@ans.pl> wrote:
> >> >>
> >> >> After upgrading to 2.6.16-rc6 I noticed this strange message:
> >> >>
> >> >>  More than 8 CPUs detected and CONFIG_X86_PC cannot handle it.
> >> >>  Use CONFIG_X86_GENERICARCH or CONFIG_X86_BIGSMP.
> >> >>
> >> >> This is a Dell PowerEdge SC1425 with two P4 Xeons with HT enabled (so with
> >> >>  totoal of 4 logical CPUs).
> >> >
> >> > Please send full dmesg output for the failing kernel, thanks.
> >>  Attached.
> >>
> >> > Which is the most-recently-tested kernel which behaved correctly?
> >>  2.6.15.6
> >
> > OK, thanks.  I assume the machine's working OK?
> 
> Yes. So far no problems, only this warning.
> 
> > From my reading, you have CONFIG_HOTPLUG_CPU enabled and the machine has an
> > APIC.
> That is correct.
> 
> > I'd expect that lots of people would hit that warning but for some
> > reason they don't - possibly because most APICs don't have sufficiently
> > high version numbers?
> >

Actually, this warning should be seen on many other systems on well. We
use the bigsmp when there _or_ more than 8 CPUs or CPU_HOTPLUG is used.
So, in that sense the message is wrong, it should also have CPU_HOTPLUG in
there. Or we should make CPU_HOTPLUG depend on GENERIC_ARCH or auto select
GENERIC_ARCH with hotplug at the CONFIG level.

Will defer to Ashok for a proper fix.

Thanks,
Venki