Re: More than 8 CPUs detected and CONFIG_X86_PC cannot handle it on2.6.16-rc6

[Krzysztof Oledzki]

On Sun, 12 Mar 2006, Venkatesh Pallipadi wrote:

> On Sun, Mar 12, 2006 at 02:05:00PM +0100, Krzysztof Oledzki wrote:
> > On Sun, 12 Mar 2006, Andrew Morton wrote:
> >
> > > Krzysztof Oledzki <olel@xxxxxx> wrote:
> > > > On Sat, 11 Mar 2006, Andrew Morton wrote:
> > > >
> > > > > Krzysztof Oledzki <olel@xxxxxx> 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.

Why? I have exactly 4 HT CPUs (2 cores), no more. I use CPU hotplug so I 
can disable or enable any of them when I want to. So, this is a classic 
SMP system and 2.6.15 is totally happy with this. Or is there any other 
(better?) way to disable/enable CPU (especially second logical CPU from 
HT) on running systems?

Best regards,

				Krzysztof Olędzki