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SubjectRe: [PATCH] x86: Allow NR_CPUS=1024
On Sun, Nov 03, 2013 at 09:29:16AM -0500, Prarit Bhargava wrote:
> On 11/03/2013 05:18 AM, Ingo Molnar wrote:
> >
> > * Josh Boyer <jwboyer@redhat.com> wrote:
> >
> >> The current range for SMP configs is 2 - 512, or a full 4096 in the case
> >> of MAXSMP. There are machines that have 1024 CPUs in them today and
> >> configuring a kernel for that means you are forced to set MAXSMP. This
> >> adds additional unnecessary overhead. While that overhead might be
> >> considered tiny for large machines, it isn't necessarily so if you are
> >> building a kernel that runs across a wide variety of machines. We
> >> increase the range to 1024 to help with this.
> >>
> >> Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
> >> ---
> >> arch/x86/Kconfig | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> >> index f67e839..d726b2d 100644
> >> --- a/arch/x86/Kconfig
> >> +++ b/arch/x86/Kconfig
> >> @@ -825,7 +825,7 @@ config MAXSMP
> >> config NR_CPUS
> >> int "Maximum number of CPUs" if SMP && !MAXSMP
> >> range 2 8 if SMP && X86_32 && !X86_BIGSMP
> >> - range 2 512 if SMP && !MAXSMP
> >> + range 2 1024 if SMP && !MAXSMP
> >> default "1" if !SMP
> >> default "4096" if MAXSMP
> >> default "32" if SMP && (X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000)
> >
> > Any reason not to allow it to go up to 4096? The original concern was that
> > CPUS=4096 wasn't working very well and you had to select MAXSMP
> > deliberately and keep all the pieces.
> >
> > But today it's all pretty robust so I see no reason why not to allow up to
> > 4096 CPUs.
>
> Adding Russ from SGI as they are one of the consumers of a large CPU count.
>
> I have no objections to raising this to 4096 FWIW. I think it is a good idea,
> and it is long overdue.

I obviously agree with increasing to 4096.
The bigger the better.

--
Russ Anderson, OS RAS/Partitioning Project Lead
SGI - Silicon Graphics Inc rja@sgi.com


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