2007-02-20 00:07:28

by Adrian Bunk

Subject: x86_64: up to 255 or 256 CPUs?

Quoting arch/x86_64/Kconfig:

<-- snip -->

...
config NR_CPUS
int "Maximum number of CPUs (2-256)"
range 2 255
...


<-- snip -->

cu
Adrian

--

"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed

2007-02-20 00:45:41

by William Lee Irwin III

Subject: Re: x86_64: up to 255 or 256 CPUs?

On Tue, Feb 20, 2007 at 01:06:47AM +0100, Adrian Bunk wrote:
> Quoting arch/x86_64/Kconfig:
> <-- snip -->
> ...
> config NR_CPUS
> int "Maximum number of CPUs (2-256)"
> range 2 255
> ...
> <-- snip -->
> cu
> Adrian

The broadcast APIC ID clashes with the 256th cpu.


-- wli

2007-02-20 09:41:20

by Andi Kleen

Subject: Re: x86_64: up to 255 or 256 CPUs?

On Tuesday 20 February 2007 01:42, William Lee Irwin III wrote:
> On Tue, Feb 20, 2007 at 01:06:47AM +0100, Adrian Bunk wrote:
> > Quoting arch/x86_64/Kconfig:
> > <-- snip -->
> > ...
> > config NR_CPUS
> > int "Maximum number of CPUs (2-256)"
> > range 2 255
> > ...
> > <-- snip -->
> > cu
> > Adrian
>
> The broadcast APIC ID clashes with the 256th cpu.

Yes 255 is theory. But we don't know if it actually works anyways because
it has been never tested.

-Andi